INFORMATION TO USERS This rep ro d u ctio n was m ade from a copy o f a d o c u m e n t sent to us for m icrofilm ing. While th e m ost advanced technology has been used to photograph and reproduce this d o c u m e n t, the quality o f the rep ro d u ctio n is heavily d ependent upon the quality o f th e m aterial su b m itted . The follow ing explanation o f techniques is provided to help clarify m arkings or n o tatio n s which may appear on this rep ro d u ctio n . 1 .T h e sign or “ ta rg e t” fo r pages apparently lacking from the docum ent p h o tographed is “ Missing Page(s)” . If it was possible to obtain the missing page(s) o r section, they are spliced into the film along w ith adjacent pages. This m ay have necessitated cu ttin g through an image and duplicating adjacent pages to assure com plete co n tin u ity . 2. W hen an image on th e film is o bliterated with a round black m ark, it is an indication o f e ith e r blurred copy because o f m ovem ent during exposure, duplicate copy, o r copyrighted m aterials th a t should n o t have been film ed. F or blurred pages, a good image o f the page can be found in the adjacent fram e. If copyrighted m aterials were d eleted, a target note will appear listing th e pages in the adjacent fram e. 3. W hen a m ap, draw ing o r ch art, e tc ., is p a rt o f the m aterial being p h otographed, a definite m ethod o f “ sectioning” th e m aterial has been follow ed. I t is custom ary to begin film ing at the u p p er left hand c o m e r o f a large sheet and to co n tinue from left to right in equal sections with small overlaps. If necessary, sectioning is continued again—heeinning below th e first row and continuing on until com plete. 4. F o r illustrations th a t c an n o t be satisfactorily reproduced by xerographic m eans, photographic p rin ts can be purchased at additional cost and inserted into y o u r xerographic copy. These p rin ts are available upon request from the D issertations C ustom er Services D epartm ent. 5. Some pages in any d o c u m e n t m ay have indistinct p rint. In all cases the best available copy has been film ed. University Micrxjfilms International 300 N. Zeeb Road Ann Arbor, Ml 48106 8400621 Rolim , Antonio Edilton LABORATORY COMPARISON OF THE POTENTIAL OF APANTELES RUFICRUS HALIDAY AND APANTELES MILITARIS WALSH (HYMENOPTERA: BRACONIDAE) FOR CONTROL O F THE ARMYWORM, PSEUDALETIA UNIPUNCTA (HAWORTH) (LEPIDOPTERA: NOCTUIDAE) IN MICHIGAN M ichigan State University University Microfilms International 300 N. Zeeb R oad, Ann Arbor, Ml 48106 Ph.D. 1983 LABORATORY COMPARISON OF THE POTENTIAL OF APANTELES RUFICRUS HALIDAY AND APANTELES MILITARIS WALSH (HYMENOPTERA: BRACONIDAE) FOR CONTROL OF THE ARMYWORM, PSEUDALETIA UNIPUNCTA (HAWORTH) (LEPIDOPTERA: NOCTUIDAE) IN MICHIGAN By Antonio Edilton Rolim A DISSERTATION Submitted to Michigan S t a te University in p a r t i a l f u l f i l l m e n t o f the requirements f o r the degree of DOCTOR OF PHILOSOPHY Department of Entomology 1983 ABSTRACT LABORATORY COMPARISON OF THE POTENTIAL OF APANTELES RUFICRUS HAL IDAY AND APANTELES MILITARIS WALSH (HYMENOPTERA: BRACONIDAE) FOR CONTROL OF THE ARMYWORM, PSEUDALETIA UNIPUNCTA (HAWORTH) (LEPIDOPTERA: NOCTUIDAE) IN MICHIGAN By Antonio Edilton Rolim Following i t s i n tr o d u c ti o n from Pakistan in 1977-79, A. r u f i c r u s Haliday was s u c c e s s f u l l y rea red on the armyworm,Pseu doletia unipuncta (Haworth), in the l a b o r a to r y and r e l e a s e d in the f i e l d bu t, to date, t h e r e i s no evidence o f e stab lis h m en t. In a l t e r n a t i v e h ost t e s t s A. r u f i c r u s showed a low a c c e p t a b i l i t y f o r the noctu ids Peridroma saucia (Hiibner), Aqrotis i p s i l o n (Hufnagel), and Amathes c-nigrum ( L .) . I t s p o t e n t i a l f o r armyworm control was assess ed through comparisons with a common n a ti v e p a r a s i t o i d , A. m i l i t a r i s Walsh. In host s i z e p reference t e s t s mi 1 i t a r i s a ttac k ed a l l armyworm i n s t a r s , but p r e f e r r e d 2nd to 4th i n s t a r s . A. r u f i c r u s o v ipo site d s u c c e s s f u ll y only in 1 s t to 4th i n s t a r s . P a r a s i t o i d f u nctio n al responses in terms of hosts p a r a s i t i z e d a t c o n t r o l l e d ho st and p a r a s i t o i d d e n s i t i e s in a cage system (1.95 m su rfa ce a re a ) sim ula tin g f i e l d c o n d itio n s confirmed the su pe rio r searching c h a r a c t e r i s t i c s of m i l i t a r i s over r u f i c r u s . Mean numbers of h osts k i l l e d increas ed f o r r i s i n g host and p a r a s i t o i d d e n s i t i e s f o r both s p e c i e s , but only under very high d e n s i t i e s of both p a r a s i t o i d and host was r u f i c r u s able to p a r a s i t i z e armyworm la r v a e . Antonio Edilton Rolim Data on r ep ro d u c tiv e parameters were c o n t r a s t e d under confined, cage or f i e l d c o n d i t i o n s . Production of f o r m i l i t a r i s than f o r r u f i c r u s . progeny was always g r e a t e r Both f i e l d and cage progeny means were s i g n i f i c a n t l y lower than those produced under a s t r i c t l y confined s i t u a t i o n ( v i a l s ) . Both species made repeated a t t a c k s when confined in v i a l s which o f t e n r e s u l t e d in s u p e r p a r a sitis m . Both sp e cie s have s i m i l a r developmental c y c l e s , but r u f i c r u s has a s l i g h t l y s h o r t e r l i f e cycle (19.6 days a t 23°C a g a i n s t 22.1 days f o r m ilitaris). While an inverse r e l a t i o n s h i p e x i s t s between host i n s t a r and number of days spent by each p a r a s i t o i d in the ho st l a r v a , the average length o f pupal stag e was not influence d by the host i n s t a r in which la r v a e o r i g i n a t e d . This averaged about 7.1 days f o r m i l i t a r i s and 5.5 days f o r r u f i c r u s . DEDICATION For n\y p a r e n t s , Euclides and Hilda Rolim, a symbol of f i l i a l g r a t i t u d e . ACKNOWLEDGMENTS I am very g r a t e f u l t o the B r a z i li a n Ministry o f Education who, through CAPES and my home u n i v e r s i t y , Federal U nivers ity of Ceara a t F o r t a l e z a , has provided a l l t h e f i n a n c i a l support f o r my entomo­ lo g ic a l t r a i n i n g in the U.S. I would l i k e t o express my deepest a p p re c i a ti o n to my major p r o f e s s o r and f r i e n d Dr. Frederick Stehr f o r suggesting t h i s p r o j e c t and p a t i e n t l y a s s i s t i n g me in i t s development and successful completion. My a p p r e c i a t i o n i s extended to departmental chairman Dr. James Bath f o r h i s continued i n t e r e s t and f o r f i n a n c i a l a s s i s t a n c e which much c o n t r i b u t e d to th e completion o f my s t u d i e s . Other members o f my guidance committee were most h e l p f u l . Drs. Stanley Well so and Edward Grafius provided an e x c e l l e n t review of the manuscript and c o n t r i b u t e d several ideas incorpora te d i n to t h i s thesis. Drs. Brian C r o f t , Robert Ruppel and Alan Putnam o f f e r e d many valuable suggestions and c r i t i c i s m in the course of my graduate program. I wish to express my s i n c e r e thanks to them. Thanks are extended to the USDA through the persons of Dr. Stanley Well so and James Webster f o r making t h e i r la b o r a to r y and greenhouse f a c i l i t i e s always a v a i l a b l e to me. I s i n c e r e l y thank Dr. John Gill f o r his suggestions on s t a t i s t i c a l treatm ent of the d a ta , and Ken Dimoff f o r h is invaluable help a t the Department o f Entomology computer term ina ls. Many o t h e r people have given t h e i r time and generous a s s i s t a n c e a t the various sta g es o f t h i s p r o j e c t . In p a r t i c u l a r I wish to thank Marian R e i t e r , Mark Otto, Kasumbogo Untung, Dave Helmreich and Manoel Camara. Special thanks to my dear wife Rita whose encouragement, understanding and continued a s s i s t a n c e has made the pursuance of t h i s d octo ral degree p o s s ib l e . Deo g r a t i a s . TABLE OF CONTENTS Page LIST OF TABLES..................................................................................................... v ii LIST OF FIG URES................................................................................................. xi INTRODUCTION ......................................................................................................... 1 LITERATURE REVIEW................................................................................................. 5 The ArmywormProblem .............................................................................. The Armyworm'sNatural Enemy Complex ............................................. Aspects o f Biological Control Relevant to This Study . . . 5 7 10 METHODS AND MATERIALS .................................................................................... 18 Host and P a r a s i t o i d R e a r i n g ............................................................... Pre lim inary Tes ts With A. r u f i c r u s .............................................. Comparative T ests Between A. m i l i t a r i s and A. r u f i c r u s . . Host Size Preference T e s t s ....................................................... Functional Response Tests ....................................................... Reproduction and Development .................................. . . . . I n te r n a l Competition Tests ....................................................... 18 21 24 24 25 30 31 RESULTS AND DISCUSSION .................................................................................... 34 Host and P a r a s i t o i d F ie ld Survey ................................................... Observations on the Target H o s t .......................................... Field P a r a s i t i s m ............................................................................ Foreign P a r a s i t o i d Importation ....................................................... Crossing Tests ............................................................................ Host Range T e s t s ............................................................................ Comparative Studies Between A. m i l i t a r i s and A. r u f i c r u s . Host Size P r e f e r e n c e ................................................................... A. mil i t a r i s ........................................................................ A. r u f i c r u s ............................................................................ Responsiveness to Host Density (Functional R e s p o n s e s ) ................................................................................ Primary E f fe c t s of P a r a s i t i z a t i o n .............................. Secondary E f fe c t s o f P a r a s i t i z a t i o n ......................... P a r a s i t o i d Reproduction ........................................................... P a r a s i t o i d Development ............................................................... Induced I n terna l Competition ................................................... Im plicatio ns f o r Biological Control and General Recommendations ................................................................................ 34 34 35 38 40 43 45 45 45 48 v 57 60 70 80 100 106 Ill TABLE OF CONTENTS (C o n tin u ed ) Page LITERATURE CITED ................................................................................................. 117 APPENDIX 1 .............................................................................................................. 127 APPENDIX 2 .............................................................................................................. 129 vi LIST OF TABLES Table 1 2 3 4 5 5 7 8 9 10 11 12 Page Armyworm Larvae P a r a s i t i z e d by A. m i l i t a r i s in No-Till Corn Near St. Johns, Clinton Co., Michigan (T8N R3W Sec 2 5 ) ......................................................................................... 37 Results o f Attempted Crosses Between A. m i l i t a r i s and A. r u f i c r u s ................................................................................. 42 S u i t a b i l i t y o f Three Cutworms as A l t e r n a t e Hosts f o r A. r u f i c r u s Compared With JP. unipuncta .............................. 44 Armyworm I n s t a r s S u c c e s s f u ll y P a r a s i t i z e d by A. mil i t a r i s According to Age of Host and Age of P a r a s i t o i d ......................................................................................... 47 Armyworm I n s t a r s S u c c e s s f u ll y P a r a s i t i z e d by A. r u f i c r u s According to Age of Host and Age of P a r a s i t o i d ......................................................................................... 49 General S u s c e p t i b i l i t y and Subsequent History of _P. unipuncta Larvae Exposed in Various Stages to A. mil i t a r i s f o r a 24-hr P e r i o d .................................................. 50 General S u s c e p t i b i l i t y and Subsequent History of P. unipuncta Larvae Exposed in Various Stages to A. r u f i c r u s f o r a 24-hr P e r i o d ............................................... 51 Results o f D i s s e c tio n s on Dead Armyworm Larvae After Exposure Under Confined Conditions t o A. m i l i t a r i s o r A. r u f i c r u s ................................................................................. 55 R esu lts of D iss ec tio n s on Armyworms P a r a s i t i z e d by A. m i l i t a r i s or A. r u f i c r u s A f t e r Completion of P a r a s i t o i d Larval Emergence and Cocoon Spinning . . . . 56 Armyworms P a r a s i t i z e d by A. m i l i t a r i s and A. r u f i c r u s Females Released in a Cage with a 1.95 nr Basal Area During an 8 hr P e r i o d ...................................................... 61 Average Number of Armyworms P a r a s i t i z e d by A. m i l i t a r i s Females Released in a Cage with a 1.95 m2 Basal Area During an 8 hr P e r i o d ................................................................... 62 Average Number of Armyworms P a r a s i t i z e d by A. r u f i c r u s Females Released in a Cage with a 1.95 m2 Basal Area During an 8 hr P e r i o d ................................................................... 63 v ii LIST OF TABLES (C o n tin u ed ) Average Percent o f Armyworms P a r a s i t i z e d by A. mil i t a r i s Females Released in a Cage with a 1.95 m2 Basal Area During an 8 hr Period ........................................................................ 65 Average Percent o f Armyworms P a r a s i t i z e d by A. r u f i c r u s Females Released in a Cage with a 1.95 nr Basal Area During an 8 hr Period ........................................................................ 66 Two-factor Analysis o f Variance of P a r a s itism Rates by A. m i l i t a r i s and A. r u f i c r u s Searching f o r Three D i f f e r e n t I n s t a r s of the Host, £ . unipuncta (A = P a r a s i t o i d Sp ecie s; B = Host I n s t a r ) . . ......................... 68 T hree-Factor Analysis of Variance o f P a r a s i ti s m Rates by 5 and 10 Females of A. m i l i t a r i s Searching f o r Three D i f f e r e n t I n s t a r s of the Host, £ . unipuncta (A = P a r a s i t o i d Density; B = Host Density; C = Host I n s t a r ) ..................................................................................................... 69 Subsequent H istory o f £_. unipuncta Larvae Exposed a t Various D e n s i t ie s to 5 A. m i l i t a r i s Females in Cages 1.95 nr in Surface Area f o r 8 Hours .......................................... 71 Subsequent H istory o f P . . unipuncta Larvae Exposed a t Various D e n s i t ie s to 10 A. m i l i t a r i s Females in Cages 1.95 mz in Surface Area f o r 8 Hours .......................................... 72 Subsequent H isto ry o f P. unipuncta Larvae Exposed a t Various D e n sitie s to 1(T A. r u f i c r u s Females in Cages 1.95 m2 in Surface Area f o r 8 Hours .......................................... 73 Probable Number o f Armyworms Found by A. m i l i t a r i s and A. r u f i c r u s Females in Cage Experiments Taking i n to Account Secondary E f fe c t s of P a r a s i t i z a t i o n . . . . 75 Probable Number o f Armyworms Found by A. m i l i t a r i s Females in Cage Experiments Taking i n to Account Secondary E f f e c t s of P a r a s i t i z a t i o n .......................................... 77 Probable Number o f Armyworms Found by A. r u f i c r u s Females in Cage Experiments Taking in to Account Secondary E f f e c t s of P a r a s i t i z a t i o n .......................................... 78 Average Number o f Progeny Produced by Exposure of 2nd I n s t a r Armyworm Larvae to A. m i l i t a r i s ......................... 82 Average Number o f Progeny Produced by Exposure of 3rd I n s t a r Armyworm Larvae to A. m i l i t a r i s ......................... 83 vi i i LIST OF TABLES (C o n tin u ed ) Paae Average Number of Progeny Produced by Exposure of 4th I n s t a r Armyworm Larvae to A. m i l i t a r i s ......................... 84 Average Number o f Progeny Produced by Exposure of 2nd I n s t a r Armyworm Larvae to A. r u f i c r u s ......................... 85 Average Number o f Progeny Produced by Exposure of 3rd I n s t a r Armyworm Larvae to A. r u f i c r u s ......................... 86 Average Number o f Progeny Produced by Exposure of 4th I n s t a r Armyworm Larvae to A. r u f i c r u s ......................... 87 Average Number o f A. m i l i t a r i s Emerging from F ie ld Sampled Armyworm Larvae................................................................... 91 Average Number o f Cocoons Produced from Armyworms P a r a s i t i z e d (AP) When Confined in a Vial with One Female A. m i l i t a r i s f o r 24 Hours ............................................... 92 Total Number of Armyworms Attacked When Caged with Five A. m i l i t a r i s Females f o r 8 Hours and the Number of Fj P a r a s i t o i d Progeny Produced.............................................. 94 Total Number o f Armyworms Attacked When Caged with Ten A. m i l i t a r i s Females f o r 8 Hours and the Number of F. P a r a s i t o i d Progeny Produced...................................................... . 95 Total Number of Armyworms Attacked When Caged with Ten A. r u f i c r u s Females f o r 8 Hours and the Number of F, P a r a s i t o i d Progeny Produced.............................................. 7 . . 96 Total and Average Number of Cocoons Produced from D i f f e r e n t I n s t a r s of Armyworms P a r a s i t i z e d (AP) When Caged with Five A. m i l i t a r i s Females f o r 8 Hours . . . . 97 Total and Average Number of Cocoons Produced from D i f f e r e n t I n s t a r s o f Armyworms P a r a s i t i z e d (AP) When Caged with Ten A. m i l i t a r i s Females f o r 8 Hours................. 98 Total and Average Number of Cocoons Produced from D i f f e r e n t I n s t a r s o f Armyworms P a r a s i t i z e d (AP) When Caged with Ten A. r u f i c r u s Females f o r 8 Hours ................. 99 Duration o f A. m i l i t a r i s Life Cycle from Egg to Adult from L i t e r a t u r e and Aut hor's Observa tions.............................. 101 Duration o f A. r u f i c r u s Life Cycle from Egg to Adult from L i t e r a t u r e and A uthor's Observa tions.............................. 102 ix LIST OF TABLES (C o n tin u ed ) Tab le 39 40 41 42 Page Developmental Times from Oviposition to P a r a s i t o i d Larval Emergence from Various Armyworm I n s t a r s ................. 103 Developmental Times Between P a r a s i t o i d Larval Emergence from Various I n s t a r s to Adult P a r a s i t o i d Emergence................................................................................................. 105 P a r a s i t i z a t i o n of Early I n s t a r Armyworm Larvae Following an A. m i l i t a r i s - A. r u f i c r u s Exposure S e q u e n c e ................................................................................................. 108 P a r a s i t i z a t i o n of Early I n s t a r Armyworm Larvae Following an A. r u f i c r u s - A. m i l i t a r i s Exposure S e q u e n c e ................................................................................................. 109 x LIST OF FIGURES Page Figure 1 Schematic r e p r e s e n t a t i o n of the d i s t r i b u t i o n of f l a t s planted with b a rle y within experimental cage xi . 27 INTRODUCTION The armyworm, P s e u d a l e t ia unipuncta (Haworth), occurs from southern Canada to northwestern South America (Godfrey 1972). I t has p e r i o d i c a l l y been a major problem in the North Central region o f the U.S. and, in Michigan, out breaks have caused s u b s t a n t i a l l o s s e s r e c e n t l y t o crops such as small g r a i n s and corn (Untung 1978; Ruppel 1979b). Repeated outbreaks p o i n t to i n e f f e c t i v e r e g u l a ti o n below economic l e v e l s by i t s endemic n a tu ra l enemies, r e q u i r i n g widespread i n s e c t i c i d e tr e a tm e n t. The arrnyworm i s p a r t i c u l a r l y annoying because i t s outbreaks are u n p r e d i c t a b l e , both as to time and p la c e . Because o f i t s s p o tty d i s t r i b u t i o n during outbreaks and th e r e s u l t a n t d i f f i c u l t y to develop o r implement a management program f o r endemic n a tu r a l enemies, i t seemed to be a l i k e l y cand id ate f o r improved co ntrol by the i n tr o d u c ti o n of a new n a tu r a l energy. At the o u t s e t of t h i s p r o j e c t , a v a i l a b l e b io lo g i c a l c o ntrol reco rds suggested the f e a s i b i l i t y o f t h i s venture since previous i n tr o d u c ti o n of Apanteles r u f i c r u s Haliday i n t o New Zealand a g a i n s t th e "northern army c a t e r p i l l a r " , P s e u d a l e t ia (Mythimna) se para ta (Walker), had met with g r e a t success (Anon. 1975; Cumber e t a l . 1977). P r i o r to the i n t r o d u c t i o n , several p a r a s i t o i d s of_P. s e p a r a t a , inc luding a s t r a i n o f A. r u f i c r u s , had been e s t a b l i s h e d f o r t u i t o u s l y in New Zealand, but were a f f o r d i n g l i t t l e c o n t r o l . Since 1971 the in tr o d u c tio n of new s t r a i n s from Pakistan was very e f f e c t i v e in c o n t r o l l i n g the s p e c i e s , r e s u l t i n g in enormous savings in grain crops and p a s tu r e s (Mohyuddin and Shah 1977). Comparison o f the frequency of outbreaks in some a re a s in 1976 with the average of the previous 10 ye ars showed t h a t between 2 to 4 m illio n d o l l a r s were saved annually due to the absence of se r io u s outbreaks in p a s tu r e s alone (Hill 1977). The impact was mostly in the North Island where, a p a r t from the enormous b e n e f i t s to g razin g , increased maize production caused New Zealand t o go from importer to e x p o rte r s t a t u s . The s e l e c t i o n o f A. r u f i c r u s as a p o t e n t i a l cand idate f o r control of £. unipuncta was a ls o co nsid ere d , based on the f a c t t h a t £ . separata i s in the same genus as our local arrnyworm. In 1977, a s t r a i n of t h i s promising p a r a s i t o i d was introduced from Pakistan i n to Mid-Michigan. I t has been c u lt u r e d in an i n s e c t a r y and rele ased several times in what might be c a l l e d a " c l a s s i c a l " attempt a t improving the b io lo gical control of a na tiv e p e s t . Unfortunately, i t has not been recovered in the f i e l d to date. At the same time p relim inary t e s t i n g of a l t e r n a t i v e hosts were conducted with A. r u f i c r u s , comparative l a b o r a to r y st u d i e s were undertaken with a common n a ti v e p a r a s i t o i d , Apanteles m i l i t a r i s . These s t u d i e s were aimed a t q u a l i t a t i v e l y ev alu atin g and, i f f e a s i b l e , q u a n tify in g some of the i n t r i n s i c c h a r a c t e r i s t i c s and c a p a c i t i e s which might prevent e stablis hm ent of A. r u f i c r u s or which could otherwise i n t e r f e r e with i t s e f f e c t i v e n e s s should i t become established. The g u idelin es f o r a s s e s s in g the value of an introduced bio lo g ic al control organism are often not d i s c r e t e . However, c h a r a c t e r i s t i c s such as high searching a b i l i t y , high reproductive c a p a c i t y , and a d ap tatio n to i t s h o st have long been recognized as fundamental to i n s e c t p e s t r e g u l a t i o n and c r i t i c a l to estab lish m en t. Thus, they are d e s i r a b l e in any e f f e c t i v e n a tu ra l enemy. The number of ho sts found and p a r a s i t i z e d i s the most p r a c t i c a l means to e v a l u a t e the searching a b i l i t y o f a p a r a s i t o i d . I t can a ls o be used as a measure o f p a r a s i t o i d re p r o d u c tio n , assuming t h a t each host encountered i s o v i p o s i te d upon, which a ls o implies leaving some progeny (Hassell 1978). The experiments describe d here were devised, in p a r t , to provide information on such parameters and to asse ss which sp e cie s might be s u p e r i o r in n a tu r e . Even though both species were i n v e s t i g a t e d independently, th e e v a lu a tio n o f va rious basic p r o p e r t i e s of each in r e l a t i o n t o a common host provides some information on t h e i r com petitiv e s u p e r i o r ! t v . A. m i l i t a r i s was s e l e c t e d among several n a ti v e p a r a s i t o i d s f o r these comparative s t u d i e s because i t s frequency o f occurrence and abundance in the armyworm population were c o n s i s t e n t l y high in f i e l d samples taken from 1977 to 1980 in outbreak and non-outbreak are as (see a ls o Untung 1978). This sp e c ie s i s very well adapted t o the whole geographic range o f £ . u n i p u n c ta , showing i n t r i n s i c c h a r a c t e r i s t i c s o f s e l e c t i v i t y and synchronization with i t s host (Breeland 1958). Also, b i o lo g i c a l s i m i l a r i t i e s e x i s t between them with r e s p e c t to t h e i r morphology and behavior (Clausen 1962; Mason 1981), which makes /\. m i l i t a r i s one of the most l i k e l y endemic n a tu ra l enemies with which A. r u f i c r u s would compete in the f i e l d . I t was assumed t h a t , i f th es e sp ecies a tt a c k e d the same host and i f they overlapped in t h e i r d i s t r i b u t i o n , then com pe titive i n t e r f e r e n c e among them could e x i s t . This assumption has led to the examination of t h e i r f u nctio n al re spo n ses, rep ro d uctiv e c a p a c i t i e s and o th er charac­ t e r i s t i c s , including t h e i r r e l a t i v e r a t e s of o v i p o s i ti o n and tende ncies to s u p e r p a r a s i t i z e . Competitive i n t e r f e r e n c e , however, would only be l i k e l y to occur i f environmental c o n d itio n s favored the a d a p ta tio n o f A. r u f i c r u s t o the new h a b i t a t and i f i t s i n t r i n s i c c h a r a c t e r i s t i c s allowed i t to n a t u r a l l y e x p l o i t the t a r g e t host . In g e n e r a l , l i t t l e da ta i s a v a i l a b l e comparing la b o r a to r y r e s u l t s on the assessment of such b i o lo g ic a l parameters or on the competitive i n t e r a c t i o n s of p a r a s i t o i d species following f i e l d r e l e a s e of a new p a r a s i t o i d . This i s p r im a r ily because pre- and p o s t - i n t r o d u c t i o n s t u d i e s are u su a lly abandoned as soon as the e x o ti c n a tu ra l enemy i s found u n s u i t a b l e o r , more commonly, i f i t s e s t a b ­ lishment cannot be confirmed a f t e r several c o lo n iz a tio n r e l e a s e s . Few workers have a c t u a l l y delved in to the reasons why promising b io ­ control agents f a i l e d to adapt to t h e i r t a r g e t host (even when the h ost was found s u i t a b l e in th e l a b o r a to r y ) and to the new e nviron­ ment. I f some of thes e s t u d i e s had been continued, they would perhaps have added to our i n s i g h t o f h o s t - p a r a s i t o i d r e l a t i o n s h i p s and might have provided the answer to some of the problems in a t t a i n i n g suc cess ful b io lo g ic al c o n t r o l . LITERATURE REVIEW The Armyworm Problem For more than a c e n tu r y , the arniyworm, Ps eu d a letia unipuncta (Haworth), has been a p o t e n t i a l l y d e s t r u c t i v e p e st of cereal crops and forage g r a s s e s in the e a s t e r n h a l f of North America (Breeland 1958; Guppy 1961). In the North Central U.S., t h i s species i s a major problem, f r e q u e n t ly oc cu rrin g in widespread outbreaks (Rings and Musick 1976). Populations a re t y p i c a l l y low and occur in s c a t t e r e d l o c a t i o n s , but o c c a s i o n a l l y increase q u ic k ly , r e s u l t i n g in local outbreaks o f s e r i o u s p ro p o r t io n s . There are numerous r e p o r t s in the l i t e r a t u r e o f the n in e te e n th and e a r l y tw e n ti eth c e n t u r i e s on the ravages caused by £ . unipuncta over e x te nsive a re as ( e . g . , Riley 1883; Panton 1897; S lin g er lan d 1897; Fernald 1914; Baker 1915, 1939; B r i t t o n 1915; Gibson 1915a; Davis and S a t t e r t h w a i t 1916; Knight 1916; Walton 1916). There i s , in g e n e r a l , a c o nsid erab le amount of basic biology pu blished on the armyworm. However, the d e s c r i p t i v e approach has been used in most s t u d i e s before 1950 (Breeland 1958). R e la ti v e ly l i t t l e experimental res e a r c h on basic physiology, g e n etic s o r population ecology ( i nclu d in g p a r a s i t o i d - h o s t dynamics) has been published. Moreover, experimental work has been u su a lly r e s t r i c t e d to time periods during or following major outbreak y e a r s (Guppy 1961). 5 This lack of c o n t i n u i t y makes armyworm data somewhat u n r e l i a b l e , o r , a t b e s t , incomplete. The most comprehensive reviews on arrnyworm biology, including p a s t h i s t o r y , geographical d i s t r i b u t i o n , d e s c r i p ­ t i v e c h a r a c t e r s , l i f e h i s t o r y , n a tu ra l enemies, behavior, s e a s o n a l i t y and e a r l y control measures are found in Riley (1883), S lin g erland (1897), Davis and S a t t e r t h w a i t (1916) and, more r e c e n t l y , in Breeland (1958) and Guppy (1961), from whom the following no tes on i t s l i f e cycle a re taken. B r i e f l y summarized, the l i f e h i s t o r y and h a b i t s have been described as follow s: upon the a r r i v a l of extended warm weather, in e a r l y s p r i n g , the overw intering la r v a e complete t h e i r development, pupate in the soil and begin emerging as a d u l t s . The moths lay t h e i r eggs in t i g h t l y compact masses on the g r a s se s or the small g rains t h a t a re a v a i l a b l e e a r l y in th e season. The eggs tak e about a week to h a tc h , depending on p r e v a i l i n g tem p erature s. The newly hatched larv a e begin feeding immediately on young blades of g r a s s , giving them a general sk e leto n iz e d appearance. This kind o f feeding i s charac­ t e r i s t i c o f the f i r s t two l a r v a l i n s t a r s . These sm aller c a t e r p i l l a r s feed a t n ig h t and hide in the so il or near the crowns of the p l a n t s during the day. e v e r , n o tic e d . T herefo re, t h e i r presence in the f i e l d i s r a r e l y , i f The remaining i n s t a r s (3rd through 6th) s t r a d d l e the o u t e r margin o f the grass blade and c u t holes from the margin to the midrib u n t i l the blade i s s t r i p p e d c le a n . Armyworms e a t the above­ ground po rtio n of p l a n t s and t h e i r feeding i n c r e a s e s co n sid era b ly as they grow l a r g e r . long. When f u l l grown, the armyworm i s ca. 4 to 5 cm When t h e i r numbers a re high, l a r g e armyworms will a ls o feed during the day and may move from f i e l d to f i e l d . Pupation i s preceded by a s h o r t prepupal p e ri od o f a day o r two during which the la r v a e do not fe ed. to 3 The pupal stag e i s spent in the so il a t a depth o f about 2 cm and l a s t s approximately two weeks. In Michigan, i t i s thought t h a t t h r e e armyworm g e n eratio ns occur, the 1st ge n eratio n being the most d e s t r u c t i v e . There has been in c r e a s in g concern sin c e 1975 due to unusual consecut ive outbreaks. In 1975 and 1976, i n f e s t a t i o n s were p a r t i c u l a r l y high in wheat, rye and o a t s . Corn was the most h eavily damaged crop in 1978, and Untung (1978) argued t h a t the 1978 outbreak should be r a t e d th e most s e r i o u s in the a g r i c u l t u r a l h i s t o r y o f th e s t a t e . Control of the armyworm has l a r g e l y c o n s i s t e d of monitoring f i e l d crops f o r e a r l y d e t e c t i o n of o u t b r e a k s , followed by i n s e c t i c i d e a p p l i c a t i o n s (Ruppel 1979a; Ruppel and Bird 1981). However, timing i s a problem, sin ce tr e a tm e n ts are o f te n a p p lie d too e a r l y f o r l i g h t i n f e s t a t i o n s or too l a t e f o r heavy l a r v a l feeding (Untung 1978). t h e Armyworm's Natural Enemy Complex I t i s well-known t h a t most i n s e c t s have numerous n a tu r a l enemies which a re d i v e r s e in c h a r a c t e r i s t i c s . This i s t r u e a l s o with £. u n i p u n c t a , si nce many workers have n o tic ed t h a t whenever i t became abundant many na tu ra l enemies appeared ( s e e , f o r example, Riley 1883; S lin g er lan d 1897; Criddle 1914; Baker 1915; Gibson 1915a; Knight 1916; Mickel 1932). Large numbers were found to a t t a c k armyworm eggs, la r v a e and pupae. Coincident with the o u tb r e a k s, many ob se rv ers have r ep o rte d on the incidence of p a r a s i t i s m , but have given l i t t l e a t t e n t i o n to h o s t - p a r a s i t o i d r e l a t i o n s h i p s and t h e i r p o s s ib l e value in natu ral control. rare. P a r a s itis m s t u d i e s of non-outbreak armyworm po pulations are Thompson (1945) compiled an e x te n siv e l i s t of i n s e c t enemies o f major p e s t s includ ing £ . u n i p u n c ta , as found in the e a r l i e r l i t e r a t u r e . More r e c e n t l y , Breeland (1958) and Guppy (1967) published r a t h e r s p e c i f i c and comprehensive accounts of d i p te r o u s and hymenopt ero u s armyworm p a r a s i t o i d s . These two groups, as well as d is e a s e s ( v i r u s e s , b a c t e r i a and f u n g i ) , have long been considered to be the c h i e f f a c t o r s in population redu c tio n of the armyworm a t outbreak times (S lin g e r la n d 1897; Knight 1916; Mickel 1932). In h i s two y e ar study in Tennessee, Breeland (1958) observed, in t h e f i r s t y e a r , t h a t Diptera and Hymenoptera were almost e q u a l ly r e p r e s e n te d , 52% o f a l l rea red p a r a s i t o i d s being D iptera, and 48% Hymenoptera. y e a r , however, p a r a s i t i c Hymenoptera made up 92%. In the second Studying the armyworm in Ont ario, Guppy (1967) pointed out t h a t , o f th e 69 species of p a r a s i t o i d s noted, Hymenoptera were n e a r l y twice as numerous as Diptera (43 and 26 s p e c i e s , r e s p e c t i v e l y ) . Most o f the Hymenoptera were Braconidae, with 5 genera and 18 s p e c i e s , and Ichneumonidae, with 13 genera and 20 s p e c i e s . The Diptera were l a r g e l y Tachinidae, with 16 genera and 24 s p e c i e s . In Michigan, Untung (1978) reared 9 p a r a s i t o i d species from h i s f i e l d samples. In the genus A p a n te le s, a l a r g e genus e n d o p a r a s i t i c on va rious Lepidoptera (Muesebeck 1921; Clausen 1962), A. m i l i t a r i s i s often rea red from f i e l d - c o l l e c t e d la r v a e ( e . g . , Baker 1915; Gibson 1915b; Treherne 1916; King and Barber 1921; Vickery 1925; Schaffner and Griswold 1934). In Tennessee, Breeland (1958) found A. m i l i t a r i s to be the most predominant hymenopterous p a r a s i t o i d , accounting f o r 27% and 36% p a r a s i t i s m in two y e a r s of study. This sp ecies was a ls o found the most abundant armyworm p a r a s i t o i d in the southeaste rn p o r tio n of South Dakota (Calkins and S u t t e r 1976). Sim ila r r e p o r t s emphasizing i t s abundance o r constancy ( e . g . Baker 1915; Knight 1916; Pond 1960; Guppy 1967) r e i n f o r c e the general assumption t h a t t h i s i s indeed one of the most common n a ti v e p a r a s i t o i d s o f £ . unipuncta. In Michigan, A. m i l i t a r i s was a ls o the most p r e v a le n t hymenopterous p a r a s i t o i d recovered by Untung (1978). A. mil i t a r i s * i s a grega riou s p a r a s i t o i d n a tiv e to North America, being widely d i s t r i b u t e d in the e a s t e r n p a r t where i t a t t a c k s several noctu id hosts (Muesebeck e t a l . 1951). I t i s f a i r l y abundant in the North Central region and can a ls o be found in th e southern U.S. The biology o f A. m i l i t a r i s was f i r s t r ep o rte d in d e t a i l by Tower (1915) following a study in L a f a y e t t e , Indiana. Additional information can be found in Breeland (1958), and Calkins and S u t t e r (1976). Apanteles r u f i c r u s , with which A. m i l i t a r i s has been compared in t h i s study, i s a ls o a grega rio u s l a r v a l e n do p aras itoid recorded from a number of noctuids and p y r a l i d s in Europe, Asia, A f r i c a , A u s t r a l i a and New Zealand. Egypt. Hafez (1947) stud ied the biology and l i f e cycle in He rep orte d t h a t i t i s very abundant in are as where i t s main h o s t , Agrotis i p s i l o n Hbn., i s p r e v a l e n t . Willcocks (1937) a t t r i b u t e d an important r o l e in the control of some Agrotis and Leucania species in Egypt to t h i s p a r a s i t o i d . Furthe r a sp e c ts of the reproduction and *In h i s r e c e n t attempt a t r e c l a s s i f y i n g the Microgastrinae, Mason (1981) has s p l i t the old "A panteles" and placed both A. m i l i t a r i s and A. r u f i c r u s in the t r i b e C o t e s i i n i ; m i l i t a r i s has been t r a n s f e r r e d to the genus Glyptapanteles Ashmead 1905, and r u f i c r u s to the genus Cotesia Cameron 1891. 10 development of A. r u f i c r u s are disc ussed l a t e r with r e s p e c t to the r e s u l t s obtained in t h i s study. Aspects of Biological Control Relevant to This Study A reductio n in the use o f chemical p e s t i c i d e s and the search f o r more e cologic al approaches to i n s e c t p e s t co ntrol have long been advocated, as shown in the works o f e a r l y entomologists ( e . g . , Woodworth 1896, 1908; Smith 1941; Michelbacher 1945, among o t h e r s ) . In more r e c e n t times, the in c r e a s in g complexity of crop p r o t e c t i o n problems coupled with those induced by heavy chemical usage ( e . g . , i n s e c t i c i d e r e s i s t a n c e , resurgence of t a r g e t p e s t s , d e s t r u c t i o n of b e n e f i c i a l i n s e c t s , adverse e f f e c t s on n o n - t a r g e t organisms, environmental conta mination, e t c . ) have sti m u l a te d a g r e a t e r i n t e r e s t in the use of e cologic al p r i n c i p l e s ; t h i s has r e s u l t e d in the development and implementation o f i n t e g r a t e d p e s t management with b i o lo g ic a l control as a key component. Today, b i o lo g ic a l control c o n s t i t u t e s a c e n t r a l element in most i n t e g r a t e d control programs (Corbet and Smith 1976). Since i t s emergence in th e l a t e 1 80 0 's , the p r a c t i c e of b i o lo g ic a l control has undergone over the y e a r s a d i s t i n c t dichotomy encompassing e i t h e r the i n tr o d u c ti o n and manipulation o f ex o tic entomophagous i n s e c t s ( c l a s s i c a l b i o lo g ic a l c o n t r o l ) or the management of indigenous n a tu ra l enemies* ( n a t u r a l l y - o c c u r r i n g *In t h i s review the terms na tu ra l enemy, p a r a s i t o i d and p r e d a to r are often used in terchangeably, as a re host and prey. 11 b i o lo g ic a l c o n t r o l ) . Although the p o s s i b i l i t i e s f o r conserva tion and augmentation of n a t u r a l l y oc curring b io lo g i c a l control are many, most of the world e f f o r t u n t i l r e c e n t y e a r s was con centr ate d on " c l a s s i c a l " b io lo g ic al c o n t r o l , the ap p lied phase involving the discovery , importation and estab lish m en t of e x o t i c s (Huffaker e t a l . 1976). The main o b j e c t i v e o f " c l a s s i c a l " biocontrol has long been the search f o r e f f e c t i v e eneiTjy species in the region where the p e st o r i g i n a t e d f o r c o lo n i z a t io n in the a r e a s invaded by the t a r g e t p e st. Iri many in stan c es t h i s o b j e c t i v e has been achieved through the s e l e c t i o n and importation of one or more na tu ra l enemies. The e co lo gic al p r i n c i p l e s involved in th e importation of fo reign species a ls o apply to indigenous p e s t s wherein n a tu ra l enemies can be obtained from c l o s e l y r e l a t e d p e s t s abroad and imported to hopefully r e g u l a t e a new p e s t (DeBach 1974). Despite a number o f c r i t i c a l analyse s and new i n s i g h t s i n to the p r a c t i c e o f s e l e c t i n g b i o lo g i c a l control agents c o n tr i b u te d by several i n v e s t i g a t o r s ( e . g . , Force 1972, 1974, 1975; Price 1972, 1973; Ehler 1977, 1978, 1979; M i l le r 1977, 1980), the search f o r s u i t a b l e na tura l enemies remains, as a whole, a r a t h e r empirical process . Indeed, in most a pp lied b i o lo g ic a l control programs s e l e c t i o n has been conducted on the b a s i s of Smith's (1929) recom­ mendations, t h a t i s , by u t i l i z i n g an a s s o c i a t i o n of d i f f e r e n t species o f n a tu r a l enemies f o r each h o st. This p r a c t i c e of m u l t i p l e - s p e c i e s in tr o d u c ti o n s a g a i n s t the opposing idea o f a s i n g l e "bes t species" has become a m atter of i n te n s e debate among modern b i o lo g i c a l control workers (see Turnbull and Chant 1961; Watt 1965; Turnbull 1967; van den Bosch 1968, 1971; Huffaker e t a l . 1971; Pschorn-Walcher 1977). 12 Since t h ere are s t u d i e s which provide empirical support f o r e i t h e r view ( e . g . , Force 1974; Abies and Shepard 1976; Ehler 1977, 1978; M ille r 1977) th e controversy i s not l i k e l y to be f u l l y resolved soon. B a r t l e t t and van den Bosch (1964) and, more r e c e n t l y , Zwolfer e t a l . (1976) have reviewed and discusse d f o r e i g n e x p l o r a t i o n f o r b i o lo g ic a l control in c on sidera b le d e t a i l . Zwolfer e t a l . (1976) summarized important general c r i t e r i a t h a t may help in s e l e c t i n g n a tu ra l agents f o r i n tr o d u c t i o n . The s u b j e c t was a l s o covered e x t e n s i v e l y by DeBach (1974) who developed a s e r i e s of recommendations regard ing b i o lo g ic a l control importation p r i n c i p l e s , p o l i c i e s , and p r a c t i c e s , most of which are s t i l l v a l i d (se e a ls o DeBach 1971a). Simmonds (1972) and Messenger e t a l . (1976) concede t h a t seldom can one f o r e c a s t with confidence the outcome of any i n t r o d u c t i o n . The main reason i s because i t i s impossible to o u t l i n e a l l the b io lo g i c a l c h a r a c t e r i s t i c s necessary f o r e f f e c t i v e n e s s o f a n a tu ra l enemy in any p a rtic u la r instance. I f , however, the a t t r i b u t e s o f s u c c e s s f u l l y introduced p a r a s i t o i d s a re compared to c h a r a c t e r i s t i c s o f those which have f a i l e d , some p r o p e r t i e s emerge which are common to the most effe ctiv e species. Some o f the c h a r a c t e r s p e r t i n e n t to the e f f e c ­ ti v e n e s s o f a p a r a s i t o i d o r p r e d a t o r have been l i s t e d by Doutt and DeBach (1964), Huffaker e t a l . (1971) and Huffaker (1974). I t may be useful to r e c a p i t u l a t e some of them: (1) a marked a d a p t a b i l i t y to the varying physical c o n d itio n s of the environment; (2) adequate searching and d is p e r s a l a b i l i t i e s to f in d a s u i t a b l e host o r h a b i t a t ; (3) a high repro ductiv e c a p a c i ty r e l a t i v e to t h a t of i t s host (or prey). Other d e s i r a b l e q u a l i t i e s includ e power of prey consumption and i n t r i n s i c p r o p e r t i e s such as a high degree o f h ost s p e c i f i c i t y , sy nchr onization with host l i f e h i s t o r y , d i s c r i m i n a t i v e a b i l i t y , high s u r v i v a b i l i t y during h o s t - f r e e p e rio d s , and sp e cia l behavioral t r a i t s which may a l t e r i t s performance as r e l a t e d to d e n s i ty or d i s p e r s i o n of i t s own population (see a l s o Messenger e t a l . 1976; Zwolfer e t a l . 1976). The f i r s t t h r e e a t t r i b u t e s l i s t e d above are a l s o needed by good c o l o n i z e r s according to Mayr (1965). Messenger e t a l . (1976) have warned t h a t i t i s not to be expected t h a t a l l t h e d e s i r a b l e a t t r i b u t e s l i s t e d above w ill be sim ultaneously p r e s e n t in any p a r a s i t o i d or p r e d a t o r . I t i s g e n e r a l l y agreed t h a t among thes e the prime r e q u i s i t e f o r an e f f e c t i v e i n s e c t enemy would be a high searching c a p a c i t y , i . e . , the a b i l i t y to f i n d i t s ho st when i s scarce (Huffaker e t a l . 1976). the host As p a r a s i t o i d s and p r e d a to r s are successful to a g r e a t e r or l e s s e r e x t e n t in f i n d in g h o s t / p r e y , searching e f f i c i e n c y can be a very important parameter to e v a lu a te t h e i r performance in b i o l o g i c a l c o ntrol programs. Valuable d i s c u s ­ sions on p a r a s i t o i d se arching can be found in e a r l y papers ( e . g . , Nicholson 1933; Laing 1937; Walker 1937; Smith 1939; Thompson 1939), but more e x te n siv e assessments of searching a b i l i t y and behavior and t h e i r bearing on biocontrol have, in r e c e n t tim e s, been made by Doutt e t a l . (1976), Hagen e t a l . (1976) and Huffaker e t a l . (1976). In an a n a l y s i s o f th e concept of r - and K -s elec tion as by MacArthur and Wilson (1967), Force (1972) concludes t h a t proposed for b i o lo g i c a l control purposes e a r l y c o lo n i z e r s or r - s t r a t e g i s t s are more l i k e l y to be e f f e c t i v e because of t h e i r high reproductiv e p o t e n t i a l , high powers of d i s p e r s a l , and a b i l i t y to t o l e r a t e harsh c o n d itio n s (see Pianka 1970, 1972, f o r a more complete l i s t of the a t t r i b u t e s c h a r a c t e r i s t i c o f r - and K - s t r a t e g i s t s ) . Hence, a high 14 rep ro d uctiv e r a t e ( i n t r i n s i c power of i n c r e a s e ) would be a very important a d d it i o n a l f e a t u r e , e s p e c i a l l y in u n s t a b le , often distu rb ed environments such as agroecosystems. Using the systems a n a l y s i s approach, Hassell (1978) adds to the l i s t of c h a r a c t e r i s t i c s o f an ideal p a r a s i t o i d f o r b iocontrol the a b i l i t y t o aggregate in patches o f high h ost d e n s i t y . He e x p la in s t h a t th e high search r a t e le a d s to a g r e a t e r depress io n of the ho st e q u ilib riu m , whereas the aggregation ensures t h a t t h i s e q u il i b ri u m will be s t a b l e . Doutt (1964) and Doutt and DeBach (1964) have c h a r a c t e r i z e d the two b asic types of n a tu r a l enemies: p a r a s i t o i d s and p r e d a t o r s . A p a r a s i t i c i n s e c t ( p a r a s i t o i d ) can u su a lly be d i s t i n g u i s h e d from a p r e d a t o r by the f a c t t h a t th e former develops in or on a s i n g l e host indiv idual whereas the l a t t e r must consume more than one ho st (p rey ). In c o n t r a s t i n g these two forms, a notable f e a t u r e stands out: males, females and immature s ta g e s of p r e d a t o r s a re a l l u su a lly engaged in l o c a t i n g and consuming p rey , whereas i t i s only th e a d u l t female p a r a s i t o i d t h a t searches f o r h o s t s , and t h a t i s f o r o v ip o s i ti o n r a t h e r than to consume them, although some species do h o s t - f e e d . More r e l i a b l e , e f f i c i e n t , r e g u l a t i n g p a r a s i t o i d s o r p red a to rs are ones t h a t show a r e c i p r o c a l density-depend ent r e l a t i o n s h i p with t h e i r ho st o r prey (Huffaker and Messenger 1964). This means the host w ill be r e g u l a te d by i t s enemy, and the enemy i s in t u r n l im i t e d by the number o f h osts a v a i l a b l e . In more r e c e n t review a r t i c l e s , Doutt e t a l . (1976) and Hagen e t a l . (1976) f u r t h e r d isc u ss some of the host r e l a t i o n s h i p s of p r e d a t o r s and p a r a s i t o i d s . Some of the most r e l e v a n t asp ec ts of e a r l y i n v e s t i g a t i o n s on the dynamics o f p a r a s i t i s m and predation ( e . g . , 15 DeBach and Smith 1941, 1947; U l l y e t t 1943, 1945, 1949a, 1950; Burn ett 1951, 1953, 1954, 1956, 1958) are the abundance of the p a r a s i t o i d (or p r ed a to r) or the abundance of the ho st (or prey) as they r e l a t e to searching e f f i c i e n c y . Both p a r a s i t o i d and host d e n s i t i e s have been shown to a f f e c t the p a r a s i t o i d ' s r a t e o f reproduction through the success o f the p a r a s i t o i d in f in d in g h o s t s . Looking i n to the f a c t o r s a s s o c i a t e d with these param eters, Solomon (1949) recognized two basic responses o f p r e d a t o r s / p a r a s i t o i d s to p r e y / h o s t d e n sity : (1) a numerical response , which i s a change in p r e d a t o r / p a r a s i t o i d numbers in response t o a change in p r e y / h o s t d e n s i t y ; and (2) a functional response, which i s a change in the number of prey consumed per p r e d a t o r (or of h o sts a tt a c k e d per p a r a s i t o i d ) in response to a change in p r e y / h o s t d e n s i t y . Hassell (1966) proposed the terms "reproductive" and "behavioral" to r e s p e c t i v e l y describe both responses. These a re expressed in terms of changes in the percentage of p a r a s i t i z a t i o n or p r e d a t io n . In a s e r i e s of c l a s s i c papers, Holling (1959a, 1961, 1965, 1966) explored the terminology introduced by Solomon (1949), i d e n t i f y i n g and q u a n tif y in g several of the components of the f u n ctio n al responses. During succeeding y e ars many i n v e s t i g a t o r s have examined and expanded upon h i s approach in showing b io lo g i c a l i m p lic a tio n s of th e fu nctio nal response. Some have found a d d it i o n a l examples o f organisms e x h i b i t i n g a functional response ( e . g . , Messenger 1968; G r i f f i t h s 1969; Murdoch 1969) while o th ers have disc ussed the importance o f t h i s response in the dynamics of populations (see Murdoch and Oaten 1975, f o r a review). Huffaker e t a l . (1968) show g r a p h i c a l l y four d i f f e r e n t types o f functional responses of p a r a s i t o i d s and p red a to rs to host or prey d e n s i ty . 16 However, the basic types are only t h r e e : l i n e a r , convex and sigmoid (Hassell 1978). So f a r , such behavioral or functional responses o f entomophagous i n s e c t s have proved e s s e n t i a l in systems a n a l y s i s f o r modeling ho stp a r a s i t o i d i n t e r a c t i o n s , since they can provide a d e s c r i p t i o n of the behavior of p a r a s i t o i d s in r e l a t i o n to host d e n sity (Hassell 1978). Recognizing t h a t t h i s i s not t r u e of the behavior of p r e d a t o r s , Huffaker e t a l . (1976) cau tio n t h a t i t i s the numerical response, and not the f u n ction al response i t s e l f , t h a t i s the usual i n d i c a t o r of t h e i r control and r e g u l a t o r y power. In assaying the performance o f a p a r a s i t o i d one has f i r s t to l ea rn how i t performs as an i n d i v i d u a l , i . e . , the way in which i t searches f o r h o s t s , pe rc eives them, and f i n a l l y a ccepts or r e f u s e s them f o r a t t a c k . I t i s such functional responses o f i n d iv i d u a ls r a t h e r than the response of a population which are e s s e n t i a l f o r a c l e a r understanding and proper approach to modeling o f h o s t - p a r a s i t o i d i n t e r a c t i o n s . Modeling may in tur n lead to g r e a t e r i n s i g h t and to development o f more r e a l i s t i c s t r a t e g i e s and t a c t i c s o f p e s t control (Huffaker e t a l . 1971; Stark and Smith 1971). Hassell (1978) d i sc u sse s in d e t a i l t h e t h r e e f un ctio nal responses e a r l i e r r e f e r r e d to and e x p la in s why p a r a s i t o i d s , r a t h e r than p r e d a t o r s , make convenient experimental su b j e c t s f o r the modeling o f h o s t - n a tu r a l enemy i n t e r a c t i o n s . In d ealin g with f u r t h e r asp ec ts o f e v aluation of the impact of i n s e c t enemies, DeBach and Huffaker (1971) and, more r e c e n t l y , DeBach e t a l . (1976) have provided e x c e l l e n t reviews on a v a r i e t y of comparative experimental methods and tec hniques which may a dd i­ t i o n a l l y be employed by b i o lo g ic a l control workers (see a l s o DeBach and B a r t l e t t 1964). One o f t h e i r conclusio ns i s t h a t , a sid e from the various methods of e v a lu a tio n of e f f e c t i v e n e s s , both the f u n ction al and the numerical responses c o n s t i t u t e e s s e n t i a l t o o l s in a s s e s s in g the f u l l r e g u l a t i n g p o t e n t i a l of a given i n s e c t enemy. METHODS AND MATERIALS Host and P a r a s i t o i d Rearing All r e a r i n g and experiments were conducted a t 23.0°C ± 1.5°C, 40-60% RH, and a photoperiod o f 16 hr L : 8 hr D, using f l u o r e s c e n t 35-watt bulbs. A. m i l i t a r i s and A. r u f i c r u s were con tinuously reared in the l a b o r a to r y from April 1977 to May 1981 on £ . un ipu n cta. The h ost stock c u l t u r e was a n nu ally renewed with hundreds of armyworm la r v a e c o l l e c t e d in Mid-Michigan i n f e s t e d corn a r e a s . The A. mi 1i t a r i s c u l t u r e was formed with a d u l t s emerging from th es e f i e l d c o l l e c t e d l a r v a e . The A. r u f i c r u s c u l t u r e was renewed with a d d it i o n a l a d u l t s imported from Pakistan in 1978 and 1979. Simultaneous maintenance of a l l t h r e e i n s e c t c u l t u r e s r e q u i r e d a high degree of co o rd in a tio n and was handled as follows. For r e a r i n g the armyworm, a combination of th e procedures d e scrib e d by Pond (1960) and Guppy (1961) was used. Larvae and moths were i n i t i a l l y rea red in l arg e cages measuring 61.0 x 61.0 x 30.5 cm with f r o n t , back and bottom made of wood. The sid e s and top were made o f P l e x ig l a s and had about 30 holes 2.5 cm in diameter, evenly spaced and covered with nylon sc reening f o r v e n t i l a t i o n . However, following a d i s e a s e problem in November 1977 a b e t t e r r e a r i n g method was found wherein l a r v a e were r e a r e d in 59.1 ml c l e a r p l a s t i c cups (standard 18 19 cup or v i a l ) . * Usually no more than two la r v a e were held per cup. Although la b o r in cre ased c o n s i d e r a b ly , dampness and s a n i t a r y c o n d itio n s were more c a r e f u l l y monitored. The new method completely elim in a te d th e previous problems a s s o c i a t e d with excess moisture. Arinyworm la rv a e were fed d a i l y on f r e s h b a rle y leaves ( v a r i e t y Lakeland) which were c u t from young p l a n t s 10-15 cm t a l l and placed in each cup. The old f o l i a g e and f r a s s were removed d a i l y to prevent or minimize contamination. Prepupae were placed on s l i g h t l y moist s t e r i l i z e d s o i l s i f t e d i n t o 147.9 o r 236.6 ml wax cardboard containers.** They were u su a lly grouped 10 i n d i v i d u a l s per d ish . Containers were covered with a p e t r i dish top and kept in a secluded plac e away from l i g h t u n t i l a d u l t s emerged. On the day o f emergence a d u l t moths were t r a n s f e r r e d to metal screen sle eve cages measuring e i t h e r 30.5 x 30.5 x 30.5 cm or 45.7 x 45.7 x 45.7 cm f o r mating and o v i p o s i t i o n . Usually 20 to 40 moths of both sexes were held per cage. A 10% honey s o l u t io n and tap water were a v a i l a b l e from several cotton wads in the d i s h e s ; the s o l u t io n was changed every o t h e r day to avoid contamination. Barley s e e d lin g s p lan ted in squat c o n ta in e r s were rep laced every t h r e e days in th e cages f o r continuous egg d e po sitio n by the moths. These s e e d lin g s r a t h e r than wax paper s t r i p s as used by o t h e r workers (Pond 1960; Calkins and S u t t e r 1976), were e x c e l l e n t s i t e s f o r eg g -la yin g. Egg c l u s t e r s found on the se edling blades were ♦Supplied by Thunderbird Container Corporation, 128 Thunderbird Dr., El Paso, TX 79912. ♦♦Supplied by Continental Can Co., P a l a t i n e , IL 60067. 20 c o l l e c t e d and t r a n s f e r r e d to 472 ml Ball® wide-mouth j a r s * covered with a f i n e nylon c l o t h f o r hatching and e a r l y l a r v a l development. The l e a f m aterial placed in each j a r seemed to provide adequate moisture f o r e c l o s i o n . A few a d d it i o n a l f res h le a ves were placed in to the j a r s as soon as newly hatched l a r v a e appeared. The procedures r e p o r t e d by Calkins and S u t t e r (1976) f o r re a r in g A. m i l i t a r i s proved t o be f a i r l y s a t i s f a c t o r y . However, l a r g e r , 354.9 ml c l e a r p l a s t i c cups with a 7.6 cm diameter p e t r i dish bottom glued t o the top worked b e s t as propagating cages. cage had t h ree holes 2 .5 cm in diameter. Each p a r a s i t o i d The hole in the bottom was covered with a f i n e metal screen f o r v e n t i l a t i o n ; the o t h e r two openings were f o r supplying a 10% honey s o l u tio n and tap water from foam sponges. These s o l u t i o n s were replaced every o th er day to avoid b a c t e r i a l and/o r fungal growth. Offspring from no more than two or t h r e e cocoon masses were u s u a l ly held per c o n t a i n e r , to reduce excessive crowding, while s t i l l allowing f o r some genetic d i v e r s i t y . A fter emergence, the wasps were usua lly allowed 3-5 days f o r mating, a f t e r which a group of fem ale s, taken in small numbers from several cages, were sexed and used to p a r a s i t i z e new h o s t s . Armyworms f o r p a r a s i t i z a t i o n were u s u a l ly a v a i l a b l e from the main stock c u l t u r e as 3rd an d /o r 4th i n s t a r s . They were segrega ted two per cup (59.1 ml standard cup) with one female mated wasp. The average exposure time was 24 hours, and females o f A. m i l i t a r i s were u s u a l ly 2- or 3-days old when s e l e c t e d f o r o v i p o s i t i o n . For continuous maintenance of the p a r a s i t o i d c u l t u r e t h i s procedure had to be repeated a t 3- or 4-day ♦Supplied by Ball Corporation, Muncie, IN 47302. 21 intervals. During incubation f o r p a r a s i t o i d emergence p a r a s i t i z e d hosts were always fed f r e s h ba rl e y d a i l y . For r e a r i n g A. r u f i c r u s e s s e n t i a l l y the same technique was used. The ho st exposure method was a ls o very s i m i l a r to the one de sc ribed p reviously f o r A. m i l i t a r i s , but the ho st l o t s were comprised mostly of 2nd and/or 3rd i n s t a r s , and the wasps were u su a lly o l d e r (4-7 days). Moreover, since p a r a s i t i s m by A. m i l i t a r i s was seen to be g r e a t e r than by A. r u f i c r u s , a l a r g e r number of host la r v a e were exposed to the l a t t e r within the same 3- to 4-day period. Both p a r a s i t o i d s are in general r a t h e r s e n s i t i v e to rough handling; t h e r e f o r e , a mouth-operated a s p i r a t o r was always used to c o l l e c t them p r i o r to counting and sexing them under a microscope. As i s to be expected, during the f i v e y e a r period several m o d ificatio ns on the exposure technique of the h o st to the p a r a s i t o i d s were t r i e d and p ro g r e s s i v e l y introduced as b e t t e r methods were found. Prelim inary Tes ts With A. r u f i c r u s Two types of p relim inary t e s t s were conducted with the newlyimported A. r u f i c r u s before any comparative s t u d i e s with a n a tiv e p a r a s i t o i d species were undertaken. They c o n s i s t e d of: (1) cro ssing t e s t s , and (2) ho st range t e s t s . The c ro ssing t e s t s were conducted as a r o u t in e check of the rep roductiv e i s o l a t i o n o f t h i s p a r a s i t o i d from i t s n a ti v e "congener" A. m i l i t a r i s chosen f o r comparison. The procedure used was as follows. To prevent emerging a d u l t s from normally mating, 1 or 2 days p r i o r to emergence a number of cocoons were i s o l a t e d from t h e i r 22 o r i g i n a l c l u s t e r s , and placed sin g ly i n to standard cups. Each cup was supplied with a small pi ec e of a foam diSPO® plug s a t u r a t e d with honey water f o r p a r a s i t o i d nourishment. Following a d u l t emergence, the p a r a s i t o i d s were sexed, and v i r g i n females of one species were t r a n s f e r r e d i n to a cup cage with unmated males of the o t h e r species obtained in a s i m i l a r manner. The groups were then allowed f r e e mating f o r 2 days, a f t e r which 20 h e alth y and a c t i v e females were randomly picked from each population to make up th e experimental groups. They were introduced sin g ly i n to standard v i a l s , each female being given a 3rd i n s t a r arniyworm l a r v a as a host f o r a period of 24 hr. Twenty a d d it i o n a l females were taken from each group and se gregated with males o f t h e i r own kind t o f u n ctio n as c o n t r o l s . These a ls o each receive d a 3rd i n s t a r host l arv a f o r p a r a s i t is m . Experimental c o n d itio n s were the same f o r both groups. A f te r having been exposed to p a r a s i t o i d s , the ho sts were r e a red one per cup u n t il the emergence o f F1 progeny or pupation o f the host l a r v a . Daily o bservations were made on each individua l l a r v a , and following p a r a s i t o i d de ath, a l l F^ progeny were examined m icroscopic ally to determine sp ecies and sex, as well as t o d e t e c t any h y b r i d i z a t i o n . The host range t e s t s were designed to i n v e s t i g a t e any r e l a t i o n ­ ship between A. r u f i c r u s and p o t e n t i a l noctuid ho sts o th e r than P_. unipu n cta. Their purpose was to check f o r the s u i t a b i l i t y of d i f f e r e n t h o sts among the armyworm-1ike complex of p e s t s in the Mid-Michigan area and to compare the a c c e p t a b i l i t y of the armyworm r e l a t i v e to o th er p o s s ib l e host s p e c i e s . Host a c c e p t a b i l i t y was e s s e n t i a l l y gauged by comparing p a r a s i t i z a t i o n r a t e s f o r t h r e e cutworm species exposed to a t t a c k by A. r u f i c r u s in a confined 23 s i t u a t i o n (59.1 ml small cups). Early i n s t a r s of the v a ri e g a t e d cutworm, Peridroma saucia (Hiibner), the black cutworm, A grotis i p s i l o n (Hufnagel), and the s p o tte d cutworm, Amathes c-nigrum ( L . ) , were chosen because of t h e i r s u p e r f i c i a l l y c lo s e resemblance to the t a r g e t h o s t , and because of t h e i r a v a i l a b i l i t y and r e l a t i v e abundance among cutworm sp e cie s in Michigan. Following r e a r i n g and exposure procedures s i m i l a r to those desc ribed f o r JP. u n ip u ncta , la r v a e of th ese cutworms were u s u a l ly used as p r o sp e c tiv e h o s t s when they reached the 3rd l a r v a l i n s t a r . As u s u a l , the p a r a s i t o i d - h o s t r a t i o remained 1:1 per c o n t a i n e r f o r a f u l l 24-hour p e rio d . At the end of each t e s t the surviving females were held as a group while being given f r e s h food f o r 1 hr or so. Then, another batch of females was randomly picked among th es e wasps f o r confinement with 3rd i n s t a r armyworms f o r another 24 h r ; t h es e l a s t armyworms served as c o n t r o l s . The s i z e of the control t e s t (n) was u s u a l ly h a l f the cutworm sample because of p a r a s i t o i d m o r t a l i t y in the previous t e s t . Following the same procedure described f o r armyworms, a l l the c a t e r p i l l a r s used as p o t e n t i a l h osts were i n d i v i d u a l l y r e a r e d in standard v i a l s , f r e s h b a rle y f o l i a g e being r e g u l a r l y served a t about the same time d a i l y and always in excess of the amount consumed by the l a r v a e . In r e a r i n g l a r g e noctuid larv a e in small cups, f r e e moisture accumu­ l a t i o n may be a c r i t i c a l f a c t o r , rende ring them more s u s c e p t i b l e to d i s e a s e s o r , sometimes, i n t e r f e r i n g with molting (Pond 1960). Thus, uncut p l a s t i c l i d s used in the f i r s t 24 hr of the t e s t s to prevent p a r a s i t o i d escape from th e v i a l s were l a t e r replaced with l i d s c ut to improve a e r a t i o n f o r the l a r v a e . 24 Comparative T ests Between A. m i l i t a r i s and A. r u f i c r u s Host Size Preference Tests The main o b j e c t i v e s o f t h i s study were to i d e n t i f y d i f f e r e n t i a l p a r a s i t i s m among the vario us armyworm i n s t a r s and to note th e e f f e c t s o f d i f f e r e n t l y aged p a r a s i t o i d s on each i n s t a r . Host s i z e preference was i n v e s t i g a t e d throughout the f i r s t week o f a d u l t p a r a s i t o i d l i f e by exposing each o f the six l a r v a l i n s t a r s o f JP. unipuncta to females o f both p a r a s i t o i d s p e c i e s . Host larv a e o f each i n s t a r were s e l e c t e d from the stock c u l t u r e , based on measurements of t h e i r head capsules (see Breeland 1958). All armyworm la r v a e used were ap p aren tly h e a l t h y , well-formed and uniform in s i z e w ith in each i n s t a r . They were i n d i v i d u a l l y confined with a female wasp, presumed t o be f e r t i l i z e d , in 59.1 ml j e l l y cups f o r 24 h r s . A. r u f i c r u s wasps ranged in age from 1 t o 7 days whereas i t was more d i f f i c u l t to o b tain l a r g e numbers o f A. m i l i t a r i s 5 days or o l d e r due to t h e i r s h o r t e r a d u l t l i f e span. The females presumably mated had been p re v i o u s ly fed honey and w a t e r , but they had not o v i p o s i t e d . As u s u a l , in the days subsequent to exposure, la r v a e were r e a r e d in i s o l a t i o n , always being provided with abundant f r e s h food. Obser­ v a ti o n s were taken d a i l y u n t i l successful p a r a s i t i z a t i o n , pupation of the h o st or death from unknown causes occu rred . P a r a s i t i z e d h o sts were held u n t i l emergence o f a d u l t p a r a s i t o i d s , which were counted and sexed. I t should be noted t h a t th es e t e s t s were conducted in a very l im i te d environment where, as a r e s u l t , real p a r a s i t o i d searching was not involved. Under c o n d itio n s o f extreme confinement, excess egg 25 d e p o s i ti o n by p a r a s i t o i d s may o f ten lead to su p e r p a r a s i t is m with host death as a consequence. To i n v e s t i g a t e such a p o s s i b i l i t y microscopic d i s s e c t i o n s were performed on h ost la r v a e found p a r a s i t i z e d and on several o t h e r s dying from causes which could no t be c l e a r l y determined. The p a r a s i t o i d la r v a e they contained were counted, but not added t o the t o t a l number o f emerging mature la r v a e . Data c o l l e c t e d in th e s e t e s t s a ls o provided useful information on the e stim a tio n o f several o t h e r parameters a s s o c i a t e d with p a r a s i t o i d reproductio n and development (see below). Throughout the t e x t these t e s t s are r e f e r r e d to as "vial t e s t s " or "confined t e s t s " to d i f f e r e n t i a t e them from another s i t u a t i o n where p a r a s i t i z a t i o n took place in l a r g e cages w it h in which hosts were widely disp e rsed and t h e r e f o r e i n t e n s i v e search by the o v i p o s i t i n g females was r e q u i r e d . Functional Response Tests P a r a s i t o i d searching i s an important f a c t o r of n a tu ra l c o n t r o l . During t h i s study, i t was assumed to be a most important parameter in a p p ra i s i n g r e l a t i v e a t t a c k e f f i c i e n c y . The f un ction al res ponse , as defined by Holling (1959a,b, 1961, 1965, 1966), was thought to be a p p r o p r i a t e f o r a s se ss in g both the p a r a s i t o i d s ' searching a b i l i t i e s and t h e i r general r e g u l a to r y p r o p e r t i e s . A "cage ecosystem" was designed to sim ulate f i e l d c o n d itio n s w ithin which host and p a r a s i t o i d s would i n t e r a c t as n a t u r a l l y as p o s s i b l e . A s e r i e s of t e s t s was conducted in which known d e n s i t i e s o f the host and p a r a s i t o i d s were v a r i e d , and the r e s u l t i n g r a t e s of apparent p a r a s i t i s m were measured. Each t e s t was r e p l i c a t e d six 26 tim e s, th e time between r e p l i c a t i o n s d i c t a t e d by the a v a i l a b i l i t y of the organisms to be used. D i f f e r e n t combinations o f p a r a s i t o i d d e n s i t i e s (5 and 10), h o st d e n s i t i e s (1, 2, 4, 10, 20 and 40) and host i n s t a r s (2nd, 3rd and 4th) were examined f o r each s p e c i e s . Tests employing f i v e A. r u f i c r u s females were not c a r r i e d o ut, and a l l scheduled t e s t s using 10 A. r u f i c r u s a g a i n s t host d e n s i t i e s equal to or lower than 20 were d isc o ntin u ed since no p a r a s i t i s m was re pe ate d ly obtained. In designing t h i s a r t i f i c i a l cage system, the d u p l ic a t i o n of n a tu r a l ecosystem d e t a i l s such as ground f e a t u r e s , physiological co n d itio n of th e p l a n t , spacing, microenvironment, e t c . was a c r i t i c a l and c h alle nging endeavor. To minimize experimental e r r o r , many p relim ina ry t e s t s were conducted and data c o l l e c t i o n was not s t a r t e d u n t i l a l l the te c h n ic a l procedures seemed to have been brought under an a cc ep tab le degree of c o n t r o l . These t e s t s were conducted in two wooden cages each measuring 213.4 ( l e n g t h ) x 91.4 (width) x 30.5 ( h e ig h t) cm ( t o t a l f l o o r area: 1.95 m ) , with a f i n e mesh nylon screen on two sid e s and the top. Each cage had six hinged doors, each one measuring 58.4 x 17.8 cm. Three doors on one side of the cage opened to the o utside and permitted f u l l access t o any p o in t in the cage i n t e r i o r , making p l a n t handling an easy task while the t h r e e o th er doors were not used. Wooden f l a t s o f b a rle y se ed ling s p lan ted in rows were p o s itio n e d in the cage as shown in Figure 1. Each f l a t measured 50.8 x 35.6 x 7.6 (depth) cm ( i n s i d e measurements) and was f i l l e d with s t e r i l i z e d s o i l . The s e e d lin g s were sown in t h r e e rows about 17.5 cm a p a r t ; t h ere were about 10 p l a n t s per row. The p l a n t s were f i r s t u t i l i z e d when they 17-18cm I------------- 1 213.4cm Figure 1. Schematic r e p r e se n ta tio n of the d i s t r i b u t i o n of f l a t s planted with barley within experimental cage (Note: 6 f l a t s per cage, 8 p a r a s i t o i d food sources (X), and 2 water sources ( 0 )). 28 were 10 days o l d and c a . 15-20 cm in l e a f l e n g t h . They were u s u a l l y very s u c c u l e n t o n l y f o r two c o n s e c u t i v e t e s t days which r e q u i r e d a new ba tc h o f f r e s h p l a n t s t o be used e very o t h e r day. A l s o , th ey were l a s t w a t e r e d no l a t e r than 10-12 hours b e f o r e t e s t s were begun to minimize s o i l dampness and t o keep RH i n s i d e t h e cages s i m i l a r t o hum idity o f t h e r e a r i n g room (50% ± 10%). Both cages were i l l u m i n a t e d by f l u o r e s c e n t l i g h t s and co vered w i t h a w h i t e drop c l o t h f o r decreased b rig h tn e s s . L i g h t i n t e n s i t y , a s measured by a GE t r i p l e range 214 l i g h t m e t e r , was in t h e 140-150 f t - c r a n g e . A fan was t u r n e d on some 9-10 m away from t h e c a g e s , c r e a t i n g a g e n t l e a i r c u r r e n t th r o u g h t h e cage. Armyworm h o s t s f o r each t e s t were s e l e c t e d a t 2nd, 3rd o r 4th i n s t a r s as d e s c r i b e d e a r l i e r , s i n c e t h e s e s t a g e s were found t o be more s u s c e p t i b l e t o p a r a s i t o i d a t t a c k . They were d i s t r i b u t e d t h r o u g h ­ o u t t h e cage a r e a a t random r e l e a s e s i t e s . For each t e s t , t h e s i t e s were de te rm ine d by a random double number drawing p ro c e d u r e which i n d i c a t e d row and p l a n t p o s i t i o n w i t h i n each row. All t o g e t h e r t h e r e were a t o t a l o f 180 d i s t i n c t l o c a t i o n s t o which a h o s t l a r v a c ou ld be randomly a s s i g n e d ( e . g . , 2 . 9 = row 2 , p o s i t i o n 9; 15.3 = row 15, p o s i t i o n 3, e t c . ) . As each random s i t e was s e l e c t e d , a green p l a s t i c r i n g ( c o l l a r ) 5 cm high by 9 cm in diam was p l a c e d around t h e c o r r e s ­ ponding p l a n t ( o r group o f p l a n t s ) . Each l a r v a was p o s i t i o n e d n e a r t h e p l a n t stem su rrounded by t h e c o l l a r , a n d a b i t o f v a s e l i n e was rubbed on t h e t o p edge o f t h e c o l l a r t o p r e v e n t armyworm e s c a p e . E ig h t s t a n d a r d cups c o n t a i n i n g a sponge soaked in honey s o l u t i o n and two o t h e r cups w i t h c o t t o n wads in w a t e r were p l a c e d a t f i x e d s i t e s on t h e f l a t s t o s e r v e as a food s o u rc e f o r t h e p a r a s i t o i d s d u rin g t h e 29 8-hr t e s t . Once the f l a t s contained the proper number o f hosts (the host den sity req u ire d f o r each t e s t ) , they were t r a n s f e r r e d i n t o each cage and arranged next t o each o th er according to the setup in Figure 1. Age of the p a r a s i t o i d females used in thes e t e s t s va ried from 2-4 days f o r A. m i l i t a r i s , and from 4-8 days f o r A. r u f i c r u s . A fter females and males of each species had been s e l e c te d f o r each t e s t (an equal number of males was always r e le a s e d i n t o the cages with the fem ales), they were held to g e th e r f o r about 30 min, and then r e le as ed i n to the experimental cages c o nta in in g armyworms. The two d a i l y t e s t s always s t a r t e d in the morning with the r e l e a s e ope ra tio n and l a s t e d e x a c tl y 8 h r , usu ally being dismantled in the e a r l y evening. During the e n t i r e period the armyworm host s were a v a i l a b l e f o r p a r a s i t i zatio n by females of whatever species was searching within the cage. At the end o f the exposure p erio d, a l l f l a t s were quickly removed from in side the cages and were v i s u a l l y insp ected f o r recovery of the exposed c a t e r p i l l a r s , a process which was f a c i l i t a t e d only by the presence of c o l l a r s and damaged p l a n t s . Although most of the larv a e were found, l o s s e s were i n e v i t a b l e , f o r oft en they hid themselves very e f f e c t i v e l y or were able to c ro ss the imposed b a r r i e r . All recovered la r v a e were reared in s i n g l e cups u n t i l pupation, death or p a r a s i t o i d larv a e appeared. During the experiment, many larvae died due to unknown c a u s e ( s ) . Unparas itized hosts u su a lly pupated on schedule, in which case they were separated from the experimental group and reared s e p a r a t e l y . Cocooned p a r a s i t o i d larvae i ssu in g from k i l l e d host s were held in t i g h t - l i d d e d cups u n t il they emerged. Cocoons and a d u l t wasps were 30 l a t e r counted to determine sex r a t i o s , emergence r a t e s , and to e s tim a te the average egg d e p o sitio n per l a r v a a t t a c k e d . Reproduction and Development The experiments desc ribed p rev io u sly where s u s c e p t i b l e armyworm i n s t a r s were exposed under confined (small cups) o r sim ulated f i e l d co n d itio n s (cages) provided a l l o f th e basic data f o r a n a l y s i s and comparisons of the rep ro d u c tiv e and developmental c h a r a c t e r i s t i c s of A. m i l i t a r i s and A. r u f i c r u s . Fu rther information, including f i e l d population d a t a , were a v a i l a b l e only f o r the n a t i v e A. m i l i t a r i s through o b se rv atio n s on p a r a s i t o i d s emerging from f i e l d - c o l l e c t e d caterp illars. By making d a i l y o b se r v a tio n s on these and o t h e r lab - exposed arrnyworms i t was p o s s i b l e to study the p a r a s i t o i d s ' l i f e c y c l e , including such major ph y sio lo g ic al events as t h e i r r e p ro ­ d uctive c a p a c i t i e s ( f e r t i l i z a t i o n , fec u n dity and o v i p o s i t i o n ) and developmental times. Several measures o f p a r a s i t i s m which are d i r e c t l y or i n d i r e c t l y a s s o c i a t e d with p a r a s i t o i d reproduction have been analyzed, such as the number o f h o sts p a r a s i t i z e d by i n s t a r , the number of p a r a s i t o i d eggs l a i d per u n i t time, the number of p a r a s i t o i d eggs l a i d and a d u l t s produced per host l a r v a l i n s t a r and per ho st exposed, and p a r a s i t o i d emergence r a t e s . The average number of eggs l a i d per i n s t a r per host was e stim ated based on counts taken o f the number of cocoons spun by emerging mature l a r v a e . The percentage o f male and female progeny was determined under the microscope by examining the p ro p ortio n of both sexes among a l l a d u l t s emerging from each cocoon mass. The cocoons and males and females o f each p a r a s i t o i d species 31 possess d i a g n o s ti c c h a r a c t e r s which make t h e i r se p a r a tio n p o s s i b l e . Average emergence r a t e s were always computed from r a t e s recorded among a d u l t wasps emerging from s i n g l e cocoon masses. The m u ltip le i n t e r a c t i o n s of p a r a s i t o i d and ho st d e n s i ty r e l a t i v e to o v i p o s i ti o n r a t e and progeny production were compared with the number o f h o sts s u c c e s s f u l l y p a r a s i t i z e d by both s p e c i e s . With regard to development, before generation times o f A. m i l i t a r i s and A. r u f i c r u s were determined, a compilation was made of p e r t i n e n t da ta on developmental times from the a v a i l a b l e l i t e r a t u r e . The t o t a l du ratio n o f t h e i r l i f e cycles was assumed as being divided i n t o two developmental p e rio d s : (1) the period from p a r a s i t o i d o v i ­ p o s i t i o n in the host to l a r v a l emergence; and (2) the average length o f the "pupal" p e r i o d , i . e . , the number o f days spent by the p a r a s i ­ t o i d o u t s i d e o f the ho st to a d u l t e c l o s i o n . measured and compared f o r both s p e c i e s . These periods were both In t h i s study a l l develop­ mental data a re r e f e r r e d to the host i n s t a r in which each p a r a s i t o i d d e p o s i t s i t s eggs. This was done to show whether p a r a s i t o i d mean g e n eratio n times were influ enced by the host i n s t a r a tt a c k e d r a t h e r than by temperature a lo n e , whose e f f e c t s are already well documented (Hafez 1947; Calkins and S u t t e r 1976). This e f f e c t was i n v e s t i g a t e d s e p a r a t e l y f o r each developmental period noted p r ev io u s ly . I n t e r n a l Competition Tests In t h i s s e r i e s of t e s t s m u ltip le p a r a s i t i s m was a r t i f i c i a l l y induced by bringing armyworm ho sts and p a r a s i t o i d s t o g e t h e r in a small g l a s s chamber, and allowing females of each sp ecies to o v i p o s i t 32 in the same host l a r v a . The process was a l t e r n a t e d allowing one spe cies or the o t h e r to o v i p o s i t f i r s t . They were preceded by p i l o t t e s t s to a s s e s s : (1) the general s u s c e p t i b i l i t y of the various i n s t a r s to the procedure; (2) t h e i r a b i l i t y to bring su ccess fu l p a r a s i t i s m to term; and (3) the f e a s i ­ b i l i t y o f using apparent o v i p o s i t o r i n s e r t i o n as an i n d i c a t o r of effective parasitization. This c o n s i s t e d of l e t t i n g the female i n s e r t her o v i p o s i t o r j u s t once in the body of an armyworm l a r v a . For both p a r a s i t o i d s , the a c t io n i s in general r e a d i l y v i s i b l e due to the posture assumed by the female when " sting ing " ( o v i p o s i ti n g in) the h o st. I t should be emphasized t h a t each female was allowed to t h r u s t i t s o v i p o s i t o r in j u s t once, a f t e r which the organisms were promptly s e p ara ted . F i r s t , 2nd and 3rd i n s t a r la r v a e were s e l e c t e d f o r t h i s t e s t because o f both p a r a s i t o i d s ' known preference f o r e a r l y i n s t a r l a r v a e , and hence a n a t u r a l l y quicker a t t a c k , a most d e sir e d f e a t u r e during these t e s t s . The main steps in the exposure procedure were as follows. F i r s t , a d u l t females o f each species were sexed and then, one a t a tim e, were placed in a small chamber c o n s i s t i n g of a g l a s s 1 ml s t r a i g h t - s i d e d shell v ial con ta in ing an armyworm l a r v a . This caused both organisms to s t a y in almost d i r e c t c o n ta c t f o r a sh o rt while. P a r a s i t o i d a t t a c k u s u a l ly occurred within the f i r s t few minutes of confinement. Following the s t i n g i n g a c t the female was discarde d and the stung armyworm l a r v a was reared and observed. Four d i f f e r e n t time i n t e r v a l s between host exposure to one species or the o th er were t e s t e d : l e s s than 1 hr (simultaneous ex posu re), 24, 48 and 96 h rs. Upon spinning cocoons A. m i l i t a r i s can e a s i l y be d i s t in g u i s h e d from A. r u f i c r u s by c h a r a c t e r i s t i c s o f the cocoon and/or by morphological f e a t u r e s o f the subsequently emerged a d u l t s . RESULTS AND DISCUSSION Host and P a r a s i t o i d F ie ld Survey Observations on the Target Host Even though the development o f a p p r o p r i a te sampling methods has been used as a probable means to enable one to understand the armyworm's patchy d i s p e r s i o n (Untung 1978), i t s lo ca l and regional d i s t r i b u t i o n are s t i l l very poorly understood. Localized outbreaks a r e o ften c h a r a c t e r i z e d by t h e i r u n p r e d i c t a b i l i t y . As a r u l e , i t i s d i f f i c u l t to f i n d armyworms in the same a r e a ( s ) where d e s t r u c t i v e populations were noted the y e ar be fo re. In the outbreak a r e a s , c a t e r p i l l a r s are abundant and can be obt ained in l a r g e numbers. However, i t i s more common f o r P. unipuncta to occur, y e a r a f t e r y e a r , in widespread endemic (non-outbreak) p o p u latio n s. Under th ese circ umsta nces, they may occur a t such low numbers t h a t the cap tu re of a s i n g l e l a r v a take s hours of sweeping with a n e t. In e i t h e r s i t u a t i o n , the exac t l o c a t i o n ( s ) where populations w ill occur in the f u t u r e cannot be p re d i c t e d . These and o th er phenolo gy-rela te d problems may pose d i f f i c u l t i e s to the b i o lo g ic a l con trol worker who needs to s e l e c t an area f o r p a r a s i t o i d r e l e a s e , and t o subsequently monitor f o r e stablis h m en t and dispersal. 34 35 A 200-ha are a 6 km NW o f St. Johns, Clinton Co., Michigan, (T8N R3W Sec 2 5 ), including several n o - t i l l corn f i e l d s , was s e l e c t e d f o r r e l e a s e and monitoring o f A. r u f i c r u s . Armyworms are well known to have an o v i p o s i t i o n p refe ren c e f o r g r a s s e s over o t h e r p l a n t s (Breeland 1958, Guppy 1961), and f i e l d ob se rv atio n s reveal t h a t they o f t e n c o n c e n tr a te in n o - t i l l corn a re as with much g r a s s . One farmer in the area cust omarily p l a n te d n o - t i l l corn using a minimum of pesticides. In t h r e e of h i s f i e l d s , which were r e g u l a r l y v i s i t e d in May-June over a fo u r season period (1978-1981), armyworms c o n s i s ­ t e n t l y appeared in low to moderate numbers feeding on young corn. Where the g ra s se s were p r e v a l e n t among the c orn , armyworm populations were u s u a l ly moderate to l a r g e . The f a c t t h a t armyworm l a r v a e were found a t non-outbreak l e v e l s in the same n o - t i l l f i e l d s in four successiv e y e a r s suggested the e x is te n c e o f a r e s i d e n t population which could be used f o r monitoring d i s p e r s a l o f introduced n a tu r a l enemies. In c o n t r a s t , nearby corn f i e l d s which were t i l l e d over the same f ou r y e a r perio d did not harbor as many la r v a e as the n o - t i l l f i e l d s . This ob serv ation a ls o c o r r o b o r a te s the f i n d i n g s by Untung (1978) who suggested t h a t armyworms overw inter in Michigan. Field P a r a s i ti s m Limited o b se r v a tio n s on armyworm p a r a s i t o i d s were conducted a t the St. Johns s i t e . These c o n s i s t e d of randomly c o l l e c t i n g ca. 300-500 la r v a e every season and holding them in the l a b o r a t o r y f o r p a r a s i t o i d emergence. 36 Over a t h r e e year period (1981 not surveyed), A. m i l i t a r i s was found to be more abundant than any o t h e r p a r a s i t o i d . In 1980, f o r example, a p a r a s i t o i d survey in t h r e e a djoining corn f i e l d s revealed t h a t A. m i l i t a r i s alone accounted f o r up to 54.4% of the p a r a s i t i s m (Table 1). Most of the ho st larv a e were c o l l e c t e d as l a t e i n s t a r s . P a r a s i ti s m of o t h e r ho st developmental s t a g e s , however, o ften v a rie d from pl ac e to pl ac e and from y e ar t o y e a r . In Ju ly 1978, f o r in s t a n c e , in a small are a of a corn f i e l d a t Gull Lake, Kalamazoo Co., Michigan (T1S R9W Sec 9 ) , under a t t a c k by outbreaking armyworms, f i e l d c o l l e c t i o n s o f l a t e i n s t a r la r v a e and pupae showed t h a t the t a c h i n i d s Archytas a p i c i f e r (Walker) and Triachora u n i f a s c i a t a (Robineau-Desvoidy), both l a r v a l- p u p a l p a r a s i t o i d s , were predominant. In June of 1979 T. u n i f a s c i a t a alone was the more p r e v a l e n t p a r a s i t o i d a t St. Johns. Another t a c h i n i d , Winthemia r u f o p i c t a ( B i g o t) , always ranked high, c lo s e to A. m i l i t a r i s , among l a r v a l p a r a s i t o i d s encountered in moderate to high outbreak h ost populations (see a l s o Untung 1978). This c h a r a c t e r i s t i c v a r i a b i l i t y in the temporal and s p a t i a l d i s t r i b u t i o n o f both ho st and p a r a s i t o i d s , added to a l i m i t e d know­ ledge of the armyworm's ecosystem, re nders n a tu ra l enemy management o ptio n s impractical o r , a t b e s t , very d i f f i c u l t a t t h i s time. Despite high r a t e s of p a r a s i t i s m and an undeniable impact caused by n a tiv e p a r a s i t o i d s on armyworm p o p u l a t i o n s , t h e i r e f f e c t i v e n e s s to control sudden l o c a l i z e d outbreaks i s poor. Based on our p a s t e x p erien c e, i t appears t h a t natu ra l enemies o f the armyworm will not prevent p e ri o d i c outbreaks; however, i n s e c t i c i d e s alone may not be the be st s o l u t i o n . P e s t i c i d e s a re e f f e c t i v e t o o l s when u t i l i z e d j u d i c i o u s l y in Table 1. Field No. Armyworm Larvae P a r a s i t i z e d by A. m i l i t a r i s in No-Till Corn Near St. Johns, Clinton Co., Michigan (T8N R3W Sec 25) Colle ction Date P arasitism Range (No./25 lar v a e ) No. P a r a s i t o i d s / 25 Larvae (X ± S.D., n = 5) Percent P arasitism I 6/17/80 3 - 8 4.6 ± 1.9 18.4 II 6/24/80 3-11 6.4 ± 3.0 25.6 III 7/12/80 12 - 17 13.6 ± 2.1 54.4 38 IPM programs, but excessive use can cause u ndesirable e f f e c t s ( e . g . , development o f r e s i s t a n c e and cro ss r e s i s t a n c e ) or may be detrimental to n a tu ra l enemies, i n cr e as in g the chances f o r more freq uent or severe outbreaks. Such problems f r e q u e n t ly n e c e s s i t a t e f u r t h e r i n s e c t i c i d e use and in cre ase the c o s t s o f crop pr oduction. The o p po rtu nity e x i s t s to t r y d i f f e r e n t con trol approaches such as the c o lo n i z a t io n o f foreig n na tu ra l enemies of known p o t e n t i a l . Foreign P a r a s i t o i d Importation Throughout i t s long h i s t o r y of outbreaks and i n j u r y to crops r e f e r r e d to e a r l i e r , the armyworm has never been the o b j e c t o f a formalized b i o lo g ic a l c ontrol p r o j e c t . There are apparen tly no reco rds p r i o r to 1977 of in troducin g f o reig n n atu ral enemies to improve c ontrol o f the s p e c i e s in the c o n tin e n ta l U.S. (Clausen e t a l . 1977). The success obtained with new s t r a i n s of A. r u f i c r u s d i f f e r e n t from those a lr eady e s t a b l i s h e d in New Zealand (Cumber e t a l . 1977, Mohyuddin and Shah 1977) has demonstrated f o r arntyworms the v a l i d i t y o f a p r i n c i p l e which i s now becoming widely accepted; the matching of p a r a s i t o i d and host s t r a i n s i s c r i t i c a l f o r e f f e c t i v e b i o lo g ic a l control. Several d i f f e r e n t " s t r a i n s " of a p a r a s i t o i d should t h e r e f o r e be introduced to obtain maximum genetic v a r i a b i l i t y . In t h i s way, i t i s more l i k e l y t h a t a s u i t a b l e genotype f o r a p a r t i c u l a r s i t u a t i o n can be found, thus i n cre as ing the chances f o r establishm ent (Simmonds 1963). 39 P a r a s i t o i d shipment followed by l a b o r a to r y propagation and p e rio d ic f i e l d c o lo n i z a t io n of A. r u f i c r u s in Michigan was s t a r t e d in 1977. Live specimens were f i r s t s e n t from Lahore, Pakistan, via Newark, Delaware, to our i n s e c t a r y a t Michigan S t a te U n i v e r s i ty , East Lansing, in April 1977. The l i v e m aterial screened by the U.S.D.A. qu aran tin e f a c i l i t y ( B en eficial I n s e c t s Research Laboratory, Newark, DE) was intended f o r immediate f i e l d r e l e a s e as well as f o r f u t u r e study and e v a l u a t i o n . These f i r s t shipments c o n s i s t e d of a r e l a t i v e l y small l o t : 327 females and 220 males. Some a d u l t s (255) were immediately r e l e a s e d a t the Michigan S t a t e U n iv e rs ity Kellogg Gull Lake Biological S t a t i o n , whereas the remaining i n d iv i d u a ls were used to s t a r t a la b o r a to r y c u l t u r e . Additional shipments were received in May 1978 (39 a d u l t s ; 29 females and 10 males) and May 1979 (1212 a d u l t s ; 776 females and 436 males). On the shipment form i t was s t a t e d t h a t Agrotis spp. were the usual hosts in Pakistan and t h a t t h e ho st p l a n t was Solanum tuberosum. T y p ic a l l y , newly-imported stocks were allowed t o mate with i n d iv i d u a ls of the old lab c u l t u r e f o r one or two ge nera tions before release. Several small c o lo n ie s were subsequently se parated from the i n s e c t a r y population and p e r i o d i c a l l y r e l e a s e d throughout the season in gras sy f i e l d s o f the U niv e rsity campus and/o r in o th e r a re a s in the c e n t r a l p a r t of the s t a t e which seemed s a t i s f a c t o r y in meeting h a b i t a t - h o s t requirements. Colonization r e l e a s e s were usua lly made in th e e a r l y morning or l a t e a fternoon. In 1977, only a d u l t s were r e l e a s e d , b u t , from 1978 to 1980, m a s s - p a r a s i t iz e d arinyworm larvae o f varying s i z e s were a l s o l i b e r a t e d in are as where armyworms had been d e te c te d (Appendix 1). P r i o r to 40 r e l e a s e , "pre-exposed" c a t e r p i l l a r s had been confined with a l a r g e number of wasps in a 3,785 ml (1 g a ll o n ) g l a s s j a r f o r 1-2 days f o r mass p a r a s i t i z a t i o n . I t was thought t h a t by r e l e a s i n g p r e p a r a s i t i z e d la r v a e the chances f o r survival and establishm en t would be maximized. In the 1978-80 p e rio d , fr e q u e n t host surveys were made, u sua lly between May and August, but A. r u f i c r u s was not recovered, d e s p i te the emergence o f several o th e r n a t i v e hymenopterous p a r a s i t o i d s from f i e l d - c o l l e c t e d armyworms. Perhaps the sp e c ie s was unable to adapt to t h i s new h a b i t a t or h o st. Although able to p a r a s i t i z e IP. unipuncta under l a b o r a to r y c o n d i t i o n s , A. r u f i c r u s does not appear to have the p o t e n t i a l f o r su rviving and a t t a c k i n g f i e l d armyworms. This assump­ t io n i s f u r t h e r supported by data c o l l e c t e d in la b o r a to r y t e s t s designed to a s s e s s the p a r a s i t o i d ' s general searching a b i l i t y (see page 57). U n fo rtu nate ly , c l i m a t i c t o l e r a n c e s and host r e l a t i o n s in the f i e l d could no t be v e r i f i e d , although the A. r u f i c r u s source populations came from t h e p l a i n s in Pakistan and not the f o o t h i l l s . Crossing Tests Since A. r u f i c r u s c o n s t i t u t e d a f i r s t i n tr o d u c ti o n t o t h i s c ountry, c ro s sin g t h i s sp ecies with "congeneric" forms, such as A. m i l i t a r i s , was thought to be a p o s s i b i l i t y . Since the Pakistan sp ecies had been r e a red s u c c e s s f u l l y on P_. unipuncta f o r several g e n e r a t i o n s , showing good a d a p t a b i l i t y to t h i s non-natural h o s t , th es e prelim inary t e s t s were conducted to determine the ge n etic and taxonomic i n d i v i d u a l i t y of both s p e c i e s , i . e . , to confirm o r exclude the p o s s i b i l i t y f o r la b o r a to r y or f i e l d h y b r i d i z a t i o n . 41 Despite t h e i r m u lt i p le s i m i l a r i t i e s , both species can be r e a d i ly d i f f e r e n t i a t e d by the c o l o r o f t h e i r hind coxae and the c o lo r and arrangement of t h e i r cocoons. The hind coxae are yellow in A. m i l i t a r i s and black in A. r u f i c r u s . Cocoons are white and c lo s e l y packed forming in general a s i n g l e mass in A. m i l i t a r i s , and are yellow ish in c o lo r and lo o s e ly grouped in A. r u f i c r u s . The sexes of both p a r a s i t o i d s can be d i s t i n g u i s h e d by the o v i p o s i t o r and the length of the l a s t f i v e antennal segments which are somewhat s h o r t e r in the females. I t was noted t h a t when v i r g i n females of one sp ecies were placed with males of the o t h e r s p e c i e s , a l l o f f s p r i n g c o n s i s t e d of males having c h a r a c t e r i s t i c s i d e n t i c a l to those of the female pare nt (Table 2). Both A. m i l i t a r i s and A. r u f i c r u s a re known to be arrhenotokous sp e c i e s , i . e . , u n f e r t i l i z e d females give r i s e , p a rt h e n o g e n e ti c a l ly , to a generation of males (Hafez 1947, Tower 1915). The r e s u l t s thus i n d ic a t e t h a t cro ss f e r t i l i z a t i o n did not take pl ace. During t h e i r e a r l y male-female confinement p e rio d , males of both species were a t t r a c t e d to females of the o t h e r sp e c i e s ; they often chased and t r i e d to mate with th e females. Judging from th e f i n a l r e s u l t s , however, thes e attempted matings were unsuccessful as f e r t i l i z a t i o n (or h y b r i d iz a t i o n ) did not occur. I t i s a ls o noteworthy t h a t females which did not mate with males of the o th e r s p e c i e s , l a i d more eggs than those which had a chance to mate with males of t h e i r own species (Table 2). Table 2. Results of Attempted Crosses Between A. m i l i t a r i s and A. r u f i c r u s 9 ? A. r u f i c r u s ? A. m i l i t a r i s X Observation/Rearing Outcome cf A. r u f i c r u s A. m i l i t a r i s Control X cr A. m i l i t a r i s A. r u f i c r u s Control Total Number of 15 13 14 11 Hosts Dying 4 6 6 7 Hosts Pupating 1 1 0 2 Hosts P a r a s i t i z e d (n) Average Number** of Cocoons Produced/Host 145.1 ± 15.4 96.7 ± 20.8 53.6 ± 7.6 47.5 ± 10.7 Adults Emerged/Host 122.5 ± 14.6 76.6 ± 15.5 48.4 ± 7.1 43.8 ± 10.7 Average Percent*5 of Female Offspring/Host Male Offspring/Host Emergence Rate ( %) 0.0 4.9 0.0 100.0 88.9 ± 4.9 100.0 84.4 79.2 90.3 a20 host larvae used per t e s t . ^Mean ± S.E. (n = no. of p a r a s i t i z e d host l a r v a e ) . 11.1 ± 49.6 ± 8.0 50.4 ± 92.2 8.0 43 Host Range Tests A fter £ . unipuncta had proved a v ia b le f a c t i t i o u s host f o r A. r u f i c r u s , under l a b o r a to r y c o n d i t i o n s , t h ree o t h e r Michigan cutworms were a ls o evaluated f o r h o st s u i t a b i l i t y , namely: (1) the v a rie g a te d cutworm, Peridroma saucia (Hbn.), probably the most important cutworm on v e g etab les ; (2) the black cutworm, Agrotis i p s i l o n (H fn .) , a major corn p e st and rep orte d as a s a t i s f a c t o r y ho st in Egypt (Hafez 1947), and (3) the sp otted cutworm, Amathes c-nigrum (L.)» which i s l e s s important than the o t h e r two s p e cie s. Compared with P s e u d a le tia as a h o s t , e a r l y i n s t a r s (2nd and 3rd) o f th ese noctuids were l e s s vul nerable to A. r u f i c r u s , thus re v e alin g t h e i r l i m i t e d p o s s i b i l i t y as a l t e r n a t e h o s t s (Table 3 ). Low p a r a s i - t i z a t i o n r a t e s were followed by very few p a r a s i t o i d la r v a e pupating. From a t o t a l of 15 cocoons produced from t h r e e p a r a s i t i z e d £ . s a u c i a , f o r example, only two la r v a e reached the a d u l t s t a g e . From two p a r a s i t i z e d A. i p s i l o n , only seven l a r v a e and t h r e e a d u l t s emerged (data not shown in Table 3 ). In c o n t r a s t , s i g n i f i c a n t l y higher values of 54.1 (S.D. = 31.7) cocoons and 50.1 (S.D. = 31.0) emerged p a ra ­ s i t o i d s r e s u l t e d from control armyworms in th e whole t e s t (n = 34). The r e s u l t s are somewhat s u r p r i s i n g with r e s p e c t t o p a r a s i t is m o f the black cutworm, since the o r i g i n a l h osts in Pakistan were Agr otis s p p . , and A. i p s i l o n was a ls o a s a t i s f a c t o r y host in Egypt (Hafez 1947). However, the p o s s i b i l i t y of d i f f e r e n t species or s t r a i n s of the p a r a s i t o i d i s s u b s t a n t i a l since the system atics of Apanteles i s poorly known (Mason 1981). Table 3. S u i t a b i l i t y of Three Cutworms as A ltern a te Hosts f o r A. r u f i c r u s Compared with P. unipuncta Percentage of Hosts P. saucia (n = 80) P. unipuncta (n = 40) P a r a s i ti z e d 3.8 35.0 Dying from Unknown Cause 5.0 91.2 Pupated aMost died from superparasitism. A. i p s i lo n (n = 50) P. unipuncta (n = 25) A. c-nigrum (n = 40) P. unipuncta (n = 20) 4.0 40.0 0.0 50.0 55.0a 12.0 52.0a 10.0 45.0a 10.0 84.0 8.0 90.0 5.0 45 P a r a s i t i z e d cutworms e x h ib i t e d e a r l y signs of p a r a s i t i s m through low food consumption. They a ls o looked somewhat smaller than t h e i r unparasitized siblings. Some la r v a e died during r e a r i n g due to unknown c a u s e ( s ) , but most of the cutworms pupated within 2-3 weeks. I t is p o s s ib l e t h a t most l a r v a l and some pupal m o r t a l i t y may be connected with p a r a s i ­ t is m , resembling what happened to the armyworms (see the next se ction on h o s t siz e p r ef e r en c e) as a consequence of p a r a s i t o i d development or of o t h e r adverse e f f e c t s due to p a r a s i t o i d o v i p o s i ti o n (Vinson and Iwantsch 1980). Comparative S tud ies Between A. m i l i t a r i s and A. r u f i c r u s Host Size Preference A. m i l i t a r i s In studying p a r a s i t i c a s s o c i a t i o n s among lep id o p tero u s s p e c i e s , few workers have s t r e s s e d the importance of r e l a t i n g r a t e s o f p a r a s i t i s m found to the s p e c i f i c host i n s t a r s a tt a c k e d . In South Dakota, larva e of £ . unipuncta were exposed to A. m i l i t a r i s females f o r a 4 - h r period by Calkins and S u t t e r (1975) who stud ied the e f f e c t o f ho st i n s t a r s on the l a b o r a to r y biology of t h i s p a r a s i t o i d . Even though a l l six larv a l i n s t a r s were used in t h e i r p reference t e s t s , no p a r a s i t o i d larv a e ever emerged from armyworms exposed to a t t a c k during the 1 s t , 2nd or 6th i n s t a r s . E f fe c tiv e p a r a s i t i z a t i o n was g r e a t e s t among 3rd i n s t a r larvae (70%) and 4th i n s t a r s (52%). They a l s o found t h a t the p a r a s i t o i d larv a e always emerged from 6th i n s t a r h o sts r e g a r d l e s s o f the host i n s t a r o r i g i n a l l y a tta c k e d . 46 Working with the same organisms, but under s l i g h t l y d i f f e r e n t c o n d i t i o n s , p a r t i c u l a r l y in r e l a t i o n to d u ratio n o f exposure, the p r e s e n t data show t h a t p a r a s i t i z a t i o n r a t e s may vary c o n sid era b ly . For example, i t appears t h a t j u s t by changing exposure d uration from 4 to 24 h r s , some of the a pp arently "immune" i n s t a r s re p o r te d by Calkins and S u t t e r (1976) may be a tta c k e d and s u c c e s s f u l l y p a r a s i ­ t i z e d , producing v iab le o f f s p r i n g (Table 4 ). The data show no marked d i f f e r e n c e among r a t e s o f p a r a s i t i s m when age of p a r a s i t o i d i s the v a r i a b l e considered. The p a r a s i t o i d a t t a c k s the whole range o f la r v a l i n s t a r s (even those r e p o r t e d ly unattacked by Calkins and S u t t e r (1976')), but with a v a r i a b l e degree o f success. I t i s probable t h a t , in the course of the experiment, a few la r v a e were "stung" a f t e r having molted i n to the next developmental stage. However, t h i s was probably avoided by excluding th ose host s e x h i b i t i n g signs of imminent molt. Considering a l l the la r v a e p a r a s i t i z e d in th e s e t e s t s (149), the m a jo r ity of p a r a s i t is m was found among 4 t h , 3rd and 2nd l a r v a l i n s t a r s , in decreasing o rder o f pre f e r e n c e . Fourth i n s t a r la r v a e were the most h eav ily p a r a s i t i z e d (70.0%); t h i r d i n s t a r s ranked next (63.3%). Thus, under confined c o n d it i o n s , A. m i l i t a r i s has a broad a t t a c k behavior, showing th e h i g h e s t success a g a i n s t 2nd, 3rd and 4th i n s t a r s , reduced success a g a i n s t 1st and 5th i n s t a r s , and the l e a s t success a g a i n s t 6th i n s t a r s (only 5% were s u c c e s s f u l l y a t t a c k e d ) . The data a ls o show t h a t with in creased length o f exposure i t i s p o s s ib l e to obtain higher p a r a s i t i s m r a t e s covering the complete range of larval in s ta rs . Table 4. Armyworm In s ta rs S u c c e s s fu lly P a ra s itiz e d by A. m i l i t a r i s According to Age o f Host and Age o f P a ra s ito id P a r a s i to i d Age in Days Armyworm Instara ONE THREE FIVE TOTALS Freq. Freq. % Freq. % Freq. % 1 st 9 45.0 2 10.0 5 25.0 16 26.7 2nd 12 60.0 7 35.0 12 60.0 31 51.7 3rd 13 65.0 12 60.0 13 65.0 38 63.3 4th 13 65.0 16 80.0 13 65.0 42 70.0 5th 7 35.0 7 35.0 5 25.0 19 31.7 6th 1 5.0 0 0.0 2 10.0 3 5.0 aNumber of larvae per i n s t a r per t e s t was 20. % 48 A. r u f i c r u s Using mostly A g rotis la r v a e as the a v a i l a b l e h o s t , Hafez (1947) rep orte d t h a t 3rd and 4th i n s t a r s appear t o be the most s u i t a b l e l a r v a l i n s t a r s f o r e f f e c t i v e p a r a s i t i z a t i o n by A. r u f i c r u s . He found t h a t t h i s p a r a s i t o i d may a l s o lay i t s eggs in 1st and 2nd i n s t a r l a r v a e , but the ho st i s u s u a l ly k i l l e d . U t i l i z i n g P_. unipuncta as the h o s t , t h i s study r e v e a l s a d e f i n i t e p refe ren c e f o r o v i p o s i t i o n in 1st through 3rd i n s t a r la r v a e (Table 5). Second i n s t a r s showed the h i g h e s t apparent s u s c e p t i b i l i t y t o p a r a s i t o i d a t t a c k (43.8%), followed by 3rd i n s t a r s (40.0%). In t h i s t e s t s e r i e s , a t o t a l of 480 armyworm la r v a e were used, and 5th or 6th i n s t a r s were never s u c c e s s f u l l y p a r a s i t i z e d . This compares favorably with H afez's (1947) f i n d in g s where 5th i n s t a r Agrotis la r v a e were r a r e l y a tt a c k e d and 6th i n s t a r s never a tta c k e d . The means per i n s t a r per t e s t o f la r v a e p a r a s i t i z e d by A. r u f i c r u s (Table 5) are well below those p r e v io u s ly rep o rted f o r A. m i l i t a r i s (Table 4 ) . P a r a s i ti s m by A. r u f i c r u s a ls o appears t o be r e l a t i v e l y independent of the p a r a s i t o i d ' s age, a t l e a s t within i t s 1st week of adult l i f e . However, un lik e A. m i l i t a r i s , i t shows a g r e a t e r d i s c r im i n a t io n when o v i p o s i t i n g , u s u a l ly p r e f e r r i n g a narrower range o f host s i z e s . I t i s probable t h a t p e rc e n t m o r t a l i t i e s among e a r l y host i n s t a r s a tt a c k e d by each p a r a s i t o i d may a c t u a l l y be higher than shown, i f h osts dying from unknown c a u se (s) during the incubation phase are a ls o co nsi dered. Tables 6 and 7 summarize a c o l l e c t i o n of data much wider in scope, recorded to show the impact o f p a r a s i t i s m and r e a r i n g Table 5 . Armyworm In s ta rs S u c c e s s fu lly P a ra s itiz e d by A. r u fic r u s According to Age o f Host and Age o f P a ra s ito id P a r a s i to i d Age in Days ONE THREE % 1st 4 20.0 2nd 8 3rd Freq SEVENb TOTALS Freq. % Freq. % Freq. % 5 25.0 5 25.0 6 30.0 20 25.0 40.0 12 60.0 5 25.0 10 50.0 35 43.8 9 45.0 9 45.0 6 30.0 8 40.0 32 40.0 4th 2 10.0 2 10.0 1 5.0 1 5.0 6 7.5 5th 0 0.0 0 0 0.0 0 0.0 0 0.0 6th 0 0.0 0 0.0 0 o• o Freq. FIVE % o • o Armyworm Instara 0 0.0 0 0.0 aNumber of larvae per i n s t a r per t e s t was 20. bTest s e r i e s with 7-day old females was po ssible f o r A. r u f i c r u s due to i t s longer l i f e span than A. m i l i t a r i s Table 6. Arn\yworm Instar 1st General S u s c e p t i b i l i t y and Subsequent History of £_. unipuncta Larvae Exposed in Various Stages to A. m i l i t a r i s f o r a 24-hr Perioda >b Successfully Parasitized Freq. Tot. P a r a s i to i d Age (days) 1 3 5 ; % 9 2 5 1 3 5 12 7 12 3rd 1 3 5 13 12 13 4th 1 3 5 13 16 13 6th 1 3 5 1 0 2 (55.0) (51.7) 27 (63.3) (45.0) (30.0) 4 (31.7) (6.7) (5.0) ^Number of larvae per i n s t a r per t e s t was 20. bPercentages fo r t o t a l s in parentheses. 2 (3.3) 4 (6.7) 14 (23.3) 24 (40.0) 51 (85.0) 7 10 7 17 (28.3) 1 1 4 3 (18.3) 6 2 6 6 3 8 19 11 3 0 1 18 (70.0) % 0 0 2 1 2 1 42 7 7 5 33 4 8 6 38 1 3 5 (26.7) Surviving Larvae Freq. Tot. 7 2 2 8 13 6 31 5th % 4 16 13 16 2nd Unexplained Deaths Freq. Tot. 18 19 14 6 (10.0) Table 7. Armyworm Instar 1st General S u s c e p t i b i l i t y and Subsequent History of _P. unipuncta Larvae Exposed in Various Stages to A. r u f i c r u s f o r a 24-hr Period3 P a r a s i to i d Age (days) Successfully Unexplained P a r a s i ti z e d ____________ Deaths_____ Freq. Tot. % Freq. Tot. % 1 3 5 7 4 1 3 5 7 8 15 7 14 7 5 5 6 20 2nd 1 3 5 7 12 5 10 1 3 5 7 43 (43.8) 9 (53.8) 9 6 8 39 (40.0) 2 2 1 1 (48.7) (7.5) (21.2) cn 6 (7.5) 16 (20.0) 51 (63.8) 0 1 6 9 32 (40.0) 8 3 7 5 6 17 0 2 2 2 11 10 8 3 32 4th 1 8 1 7 12 6 13 8 35 3rd (25.0) Surviving Larvae__________ Freq. Tot. % 10 15 12 14 23 (28.7) Table 7. Armyworm Instar (C ontinued) P a r a s i to i d Age (days) Successfully P a r a s i ti z e d Freq Tot. 5th 1 3 5 7 0 0 0 0 6th 1 3 5 7 0 0 0 0 % Unexplained Deaths Tot. Freq % 2 3 2 4 0 (0.0) (0.0) aNumber of larvae per i n s t a r per t e s t was 20. ^Percentages f o r t o t a l s in parentheses. % 18 17 18 16 11 (13.7) 0 1 1 0 0 Surviving Larvae Tot. Freq 69 (86.3) 78 (97.5) 20 19 19 20 2 (2.5) 53 procedures on host development. They include the da ta f o r successful p a r a s i t i s m c l a s s i f i e d according to host developmental stage and p a r a s i t o i d age, as e a r l i e r examined (Tables 4 and 5 ) , as well as the q u a n t i f i c a t i o n of two o t h e r r e a r i n g outcomes, a f t e r host la r v a e have been exposed and incubated f o r p a r a s i t o i d emergence. In a d d itio n to e f f e c t i v e p a r a s i t i s m , the o t h e r p o s s i b l e outcomes are under the headings "unexplained deaths" and " surviving l a r v a e " . The former e n t a i l s armyworm larv ae dying a f t e r they were exposed to p a r a s i t o i d females. The l a t t e r r e f e r s to la r v a e which pupated normally, showing no apparent signs o f p a r a s i t i s m . In both Tables 6 and 7, the number o f de aths due to unknown c a u se (s) tends to d e c l i n e grad u a lly as one goes from the f i r s t to the l a s t i n s t a r . Among the A. m i l i t a r i s -exposed host group (Table 6 ) , 1st i n s t a r deaths were 55%, l a t e r dropping t o 10% f o r 6th i n s t a r s . In the A. r u f i c r u s group (Table 7) values f o r t h i s s o r t of m o r t a l i t y were r a t h e r s i m i l a r to those presen ted above with 53.8% f o r 1 s t and 2.5% f o r 6th i n s t a r l a r v a e . The general p a t t e r n o f t h i s unknown m o r t a l i t y i s as follo w s: in the group of la r v a e exposed to A. m i l i t a r i s (Table 6 ) , about 57% of deaths occurred w ith in the f i r s t week a f t e r exposure, 35% in 1 to 3 weeks, and f i n a l l y approximately 8% died a f t e r the t h i r d week. Among the group t h a t died a f t e r 3 weeks, t h e r e was one 1st i n s t a r l arv a which l iv e d 33 days and died as a 4th i n s t a r . This i s e x c e p ti o n a l l y long c o nsidering t h a t o t h e r 1st i n s t a r l a r v a e seemingly unaffected by p a r a s i t i s m pupated in 16-23 days a f t e r exposure. In the second group (Table 7 ) , 75% died w ithin 1 week a f t e r exposure, approximately 20% in 1 to 3 weeks, and only 5% were a l i v e a f t e r the t h i r d week. Many 54 larvae in t h i s group lik e w ise e x h ib i t e d a decreased r a t e of growth p r i o r to death. I n i t i a l l y , th ese arniyworms seem t o be he alth y ; however, they stopped feeding and, a f t e r a v a r i a b l e number of days, died. The real cause f o r death could not be determined, but i t i s suspected t h a t death of some of these l a r v a e , p a r t i c u l a r l y those larv ae which l iv e d longer but grew l i t t l e or none, may be a ss o c i a t e d with s u p e r p a r a s i t is m , r a t h e r than n a tu ra l i n f e c t i o n s . One reason f o r t h i s b e l i e f i s the g r e a t e r number o f unexplained deaths among e a r l y i n s t a r larv a e as opposed to a lower number of unexplained l a t e i n s t a r deaths where control m o r t a l i t y values were s i m i l a r . Moreover, obser­ v a tio n s made through d i s s e c t i o n s o f dead larv a e showed t h a t many were p a r a s i t i z e d , and p a r a s i t i c l a r v a l forms were sometimes seen in g re a t numbers (Table 8 ) . I n c i d e n t a l l y , many p a r a s i t o i d s were a ls o found i n s i d e c a t e r p i l l a r s from which p a r a s i t o i d larv a e had e x i t e d , showing t h a t the emergence process was not 100% success fu l (Table 9). The la r v a e which somehow avoided p a r a s i t i s m in both groups are a ls o shown in Tables 6 and 7. These d a t a , t o g e t h e r with the d a ta on unexplained m o r t a l i t y discu ssed p r e v io u s ly , i n d i c a t e t h a t l a t e i n s t a r armyworm larv a e a r e more r e s i s t a n t t o a t t a c k than e a r l y i n s t a r larvae. The reasons f o r t h i s increas ed r e s i s t a n c e have not been t o t a l l y e l u c i d a t e d , but i t may be due to in cre ased th ic k n es s of the c u t i c l e o f o l d e r larv a e (Tower 1915; Calkins and S u t t e r 1976). The p o t e n t i a l f o r p a r a s i t i s m avoidance and subsequent pupation i s a p p aren tly g r e a t e r among those l a t e i n s t a r l a r v a e exposed to A. r u f i c r u s , but i t could a l s o be due to a lack of i n t e r e s t on the p a r t of the p a r a s i t o i d . Table 8. Results of Dissections on Dead Armyworm Larvae After Exposure Under Confined Conditions to A. m i l i t a r i s or A. r u f i c r u s 3 Larvae Exposed to A. m i l i t a r i s 3 Host Sample No. Instar at Exposure Days Alive After Exposure Larvae Exposed to A. r u f i c r u s ^ No. o f A. mil. Larvae Found Instar at Exposure Days Alive After Exposure No. of A. r u f . Larvae Found 1 6th 13 0 1st 22 87 2 2nd 23 118 3rd 13 61 3 5th 15 0 3rd 14 73 4 5th 12 138 4th 12 0 5 5th 11 0 4th 12 0 6 6th 11 150 4th 4 0 7 5th 13 125 5th 7 0 8 3rd 19 0 5th 9 0 9 4th 17 0 2nd 15 65 10 4th 14 97 5th 10 0 11 - - - 3rd 11 0 12 - - - 2nd 18 42 aDead larvae d isse c te d mostly as l a t e i n s t a r s . ^Exposure time was 24 hr. 56 Table 9. Host Sampled No. Results of D issectio ns on Armyworms P a r a s i t i z e d by A. m i l i t a r i s or A. r u f i c r u s A f te r Completion o f P a r a s i t o i d Larval Emergence and Cocoon Spinning A. m i l i t a r i s Larvae ---------------------------------------Emerged and Dissected Cocoons Spun Out A. r u f i c r u s Larvae ---------------------------------------Emerged and Dissected Cocoons Spun Out 1 258 11 121 5 2 93 0 49 0 3 134 4 49 1 4 69 0 11 1 5 120 0 40 0 6 48 7 24 0 7 156 57 23 3 8 21 0 14 1 9 62 0 42 0 10 78 0 50 1 11 226 26 69 0 12 112 0 28 0 13 93 211 16 3 14 109 158 87 4 15 157 1 102 5 16 189 105 85 0 17 188 143 47 0 18 198 1 101 14 19 207 1 107 20 2 407 57 4 0 21 212 9 18 1 22 232 40 - - 23 65 98 - - 24 34 107 - - 25 97 36 - - 57 Gre ater escape r a t e s among 1st i n s t a r s were probably due to the a b i l i t y of the small la r v a e to hide more e f f e c t i v e l y under the c u t ba rle y lea v es . To avoid t h i s d i f f i c u l t y only t h r e e barley blades were supplied as la r v a l food f o r the small 1 st i n s t a r armyworms. M o r t a li t y r a t e s among c o n t r o l s as a whole v a rie d co n sid era b ly and were null among 6th i n s t a r s . The mean m o r t a l i t y of armyworm larva e used in the control population in both experiments was 14.3% (S.E. = 2 . 8 ; n = 210). The r e s u l t s o f t h e s e t e s t s , conducted as a re q u ir e d preceding ste p to o t h e r experiments (see the next s e c t i o n ) , may a ls o have some rele vanc e f o r implementation of success ful b i o lo g i c a l c o n t r o l . For example, when i t comes t o o p tim iza tio n o f b io co ntrol o r n a tu r a l enemy augmentation programs e n t a i l i n g m ass-r earin g and p a r a s i t o i d r e l e a s e , ta s k s wherein high p a r a s i t i z a t i o n r a t e s a re o f t e n r e q u i r e d (Chambers 1977), information on d i f f e r e n t i a l p a r a s i t i s m by i n s t a r s g r e a t valu e. may be of By knowing in advance which host i n s t a r s a re the most s u s c e p t i b l e to a t t a c k , h o sts can be mass-reared and exposed a t the stage(s) of g reatest v u ln erab ility . Responsiveness to Host Density (Functional Responses) The number o f progeny l e f t by i n s e c t p a r a s i t o i d s i s often determined not so much by t h e i r p o t e n t i a l egg production as by the number of host i n s e c t s which they are able t o f i n d and p a r a s i t i z e . Two important v a r i a b l e s a f f e c t i n g the number and d i s t r i b u t i o n of p a r a s i t o i d progeny a r e , t h e r e f o r e , the d e n s i ty o f th e ho st population and the number, or d e n s i t y , of female p a r a s i t o i d s searching f o r 58 s u i t a b l e ho sts (DeBach and Smith 1941, 1947; Burnett 1951, 1953, 1954). In t h i s s e c t i o n , th e e f f e c t s of v a r i a t i o n in p a r a s i t o i d and host d e n s i t y on the r a t e o f p a r a s i t i z a t i o n when females of both p a r a s i ­ t o i d s were se arching f o r host larv a e r e l e a s e d in a la b o r a to r y cage, a re examined. Each sp e c ie s was introduced s e p a r a t e l y with caged armyworm l a r v a e . Both cage ecosystems were considered l a r g e enough (1.95 m su r f a c e a re a ) t o simulate f i e l d c o n d it i o n s and e m p i r i c a l l y measure the comparative performance o f female wasps in terms o f t h e i r searching e f f i c i e n c y . P a r a s i t o i d a t t a c k r a t e s in response to c o n t r o l l e d h o st d e n s i t i e s were compared using t h e i r f u nctio n al respo nses. The p r e s e n t a t i o n of th es e data i s made in two s t e p s . F i r s t , the f u n c t i o n a l responses o f both Apanteles spe cie s are disc ussed and s t a t i s t i c a l l y compared, taking i n to account only the number and percentage o f h o sts s u c c e s s f u l l y p a r a s i t i z e d (apparent p a r a s i t i s m ) , t h a t i s , those from which v i a b l e p a r a s i t o i d progeny emerged (see page 60). In the second p a r t , secondary e f f e c t s o f p a r a s i t i z a t i o n , which were noted by d i s s e c t i o n s on dead h o st l a r v a e , are a ls o incorporate d i n t o the responses of both p a r a s i t o i d s , and th e values r e p r e s e n t h o sts a c t u a l l y discovered by the wasps ( e f f e c t i v e p a r a s i t is m ) (see page 70). This c o r r e c t i o n was thought necessary because a con­ s i d e r a b l e number o f ho st l a r v a e dying from app aren tly p a r a s i t i s m u n r e l a t e d deaths were in r e a l i t y p a r a s i t i z e d . I n i t i a l l y , i t was thought t h a t in order to compare the searc hing c h a r a c t e r i s t i c s o f both p a r a s i t o i d s and t h e i r r e l a t i v e e f f e c t i v e n e s s t h i s general t e s t scheme would be followed. F i r s t , in a s e r i e s of 59 t e s t s in v i a l s , a l l host l a r v a l i n s t a r s would be exposed to p a r a s i t i ­ z atio n as a check f o r host acceptance and/or d i s c r im i n a t io n (see page 45). Based on the r e s u l t s o f thes e t e s t s , the main experiment would then be conducted with p r e f e r r e d h o s t s . A s a tis fa c to ry basis for comparisons of p a r a s i t o i d search e f f i c i e n c y would thus be obtained by e v a l u a t i n g the a t t a c k r a t e s on i n s t a r s most l i k e l y to be p a r a s i ­ tized. In the i n i t i a l t e s t s , a v a r i e t y of d i f f e r e n t siz ed cages and several exposure times were used to determine the range o f physical variables. I t seemed l o g i c a l to use an assortment of host i n s t a r s r a t h e r than j u s t one, since previous experience had i n d ic a t e d t h a t even small host s i z e v a r i a t i o n might r e s u l t in r a t h e r v a r i a b l e parasitization rates. Had only one i n s t a r been s e l e c t e d f o r thes e t e s t s , the r e s u l t s might not have shown the wide range o f d e f i n a b le i n t e r a c t i o n s which e x i s t . This gamut of i n t e r a c t i o n s seemed, in g e n e r a l , well s u i t e d to the employment of a f a c t o r i a l design. This s t a t i s t i c a l approach has a combination of f e a t u r e s which are very useful in an e x p lo r a to r y phase o f r es ea rch when l i t t l e information i s a v a i l a b l e on the problem under i n v e s t i g a t i o n (Gill 1978a; Steel and T o rrie 1980). Functional response t e s t s were s t a r t e d in September 1980 and were completed in l a t e April 1981. Additional f i e l d t e s t s would have been deemed necessary had the imported species f a i l e d to produce any p o s i t i v e p a r a s i t i s m under l a b o r a to r y c o n d it i o n s . The outcome, how­ e v e r , provided data a t t e s t i n g to the s u p e r io r c h a r a c t e r i s t i c s o f the n a t i v e sp ecies over the imported p a r a s i t o i d . The sequence o f t a b l e s 60 which follows shows very s t r i k i n g d i f f e r e n c e s in t h e i r search capacity. Primary E f fe c t s o f P a r a s i t i z a t i o n P a r a s i t o i d fu n c tio n a l responses in terms o f host s e f f e c t i v e l y p a r a s i t i z e d were i n v e s t i g a t e d using c o n stan t d e n s i t i e s of 5 and 10 mated females. Hence, two t e s t s e r i e s were conducted fo r each p a ra sito id species. The number of hosts exposed within each s e r i e s v aried from 1 to 40. Hosts were supplied a t one o f t h r e e develop­ mental s t a g e s : 2nd, 3rd or 4th i n s t a r s . r e p l i c a t e d six times. Each i n s t a r sequence was The duratio n o f exposure was 8 hours. The two p a r a s i t o i d s d i f f e r p r i m a r il y in t h e i r r e l a t i v e a b i l i t y to f i n d and k i l l h o s t s . By and l a r g e , only under e x c e p ti o n a l l y high d e n s i t i e s o f both the p a r a s i t o i d and the host was A. r u f i c r u s able to f i n d and e f f e c t i v e l y p a r a s i t i z e armyworm l a r v a e . In c o n t r a s t , even low ho st d e n s i t i e s allowed A. m i l i t a r i s t o e f f e c t i v e l y search and p a r a s i t i z e the ho st s (Table 10). At p r a c t i c a l l y any given p a r a s i t o i d d e n s i t y A. m i l i t a r i s found in c r e a s in g numbers of ho sts as host d e n s i t y was increased. When the A. r u f i c r u s population was reduced to 5 females, no p a r a s i t i s m was observed even with the h ig h e s t number of hosts. Hence, t e s t s with l e s s than 40 h o sts proved unnecessary and were l a t e r d iscontinued. Tables 11 and 12 contain p a r a s i t i s m r a t e s f o r each sp e cie s on 2nd, 3rd and 4th i n s t a r s s e p a r a t e l y . In both cases where e i t h e r 5 or 10 A. m i l i t a r i s wasps were se arc h in g , 3rd i n s t a r hosts were p a r a s i t i z e d a t a g r e a t e r r a t e than the other instars. I t appears t h a t the p a r a s i t o i d more r e a d i l y a t t a c k s 3rd i n s t a r s than 2 nd 's or 4 t h ' s . This r e s u l t d i f f e r s with the fin d in g s in the vial t e s t s where 4th i n s t a r s were more fr e q u e n tly a ttac k ed 61 T ab le 10. Armyworms P a r a s itiz e d by A. m i l i t a r i s and A. r u fic r u s Females Released in a Cage w ith a 1 .9 5 m^ Basal Area D uring an 8 hr P e rio d 3 A. m i l i t a r i s A. r u f i c r u s Parasitoids Released Hosts Exposed Mean No. % 5 1 0.0 0.() 10 Mean No. % _ 2 .1 ± .1 2.8 ± 2.8 - - 4 .3 ± .1 6.9 ± 3.4 - - 10 .8 ± .3 7.8 ± 2.9 - - 20 1.8 ± .5 9.0 ± 2.3 - - 40 4.2 ± .9 10.5 ± 2.3 0.0 0.0 1 .1 ± .1 5.6 ± 5.6 0.0 0.0 2 .5 ± .1 25.0 ± 7.3 0.0 0.0 4 .4 ± .1 9.7 ± 3.6 0.0 0.0 10 1.9 ± .1 19.4 ± 5.9 0.0 0.0 20 3.4 ± .6 17.7 ± 3.1 .1 ± .1 40 4 .4 ± 1.0 14.0 ± 2.6 .7 ± .4 .6 ± .6 1.7 ± 1.0 aMean ± S.E. of 18 r e p l i c a t e s (6 rep s, each using 2nd, 3rd o r 4th instars). 62 T a b le 11. Average Number o f Armyworms P a r a s itiz e d by A. m i l i t a r i s Females Released in a Cage w ith a 1 .9 5 m^ Basal Area D uring an 8 h r P erio d Hosts P a r a s i t i z e d by I n s t a r a Parasitoids Released Hosts Exposed Second Third Fourth 5 1 0.0 0.0 0.0 2 0.0 0.0 4 0.0 10 .2 ± .2 .7 ± .3 .2 ± .2 10 .8 ± .3 1.2 ± .8 .3 ± .2 20 1.2 ± .5 3.3 ± 1.0 .8 ± .4 40 4.2 ± 1.4 4 .8 ± 1.6 3.5 ± 1.9 0.0 0.0 1 .2 ± .2 2 .3 ± .2 .5 ± .2 .7 ± .3 4 .7 ± .3 .3 ± .2 .2 ± .2 10 1.3 ± 1.0 2.2 ± 1.2 2.3 ± 1.0 20 3.7 ± 1.0 5.2 ± 1.1 1.5 ± 40 4 .8 ± 1.4 7.7 ± 2.5 4.0 ± 1.3 aMean ± S .E . o f 6 r e p lic a t e s . .5 63 Table 12. Average Number o f Armyworms P a r a s itiz e d by r u fic r u s Females Released in a Cage w ith a 1 .9 5 n r Basal Area D uring an 8 h r P eriod Hosts P a r a s i t i z e d by I n s t a r a Parasitoids Released Hosts Exposed Second Third Fourth 5 40 0.0 0 .0 0.0 10 1 0.0 0.0 0.0 2 0.0 0.0 0.0 4 0.0 0.0 0.0 10 0.0 0.0 0.0 0.0 0.0 20 40 .3 ± .3 1.5 ± 1.0 aMean ± S .E . o f 6 r e p lic a t e s . .5 ± .3 0.0 64 than 3 r d ' s (Table 4 ). This may be due to f a c t o r s such as the increased searching re q u ir e d in the l a r g e cages or d i f f e r e n t l a r v a l response. At the h i g h e s t host d e n s i ty used (40), an average o f about e i g h t 3rd i n s t a r la r v a e were e f f e c t i v e l y p a r a s i t i z e d by 10 females, whereas only h a l f as many were p a r a s i t i z e d when f i v e p a r a s i t o i d s were t e s t e d . The a t t a c k r a t e s were equal (Table 11). Mean numbers o f ho sts k i l l e d in creased c o n s i s t e n t l y f o r r i s i n g host d e n s i t i e s equal to or g r e a t e r than 10. The p a r a s i t i s m r a t e s showed more i r r e g u l a r i t i e s a t lower h o st d e n s i t i e s . T ests were conducted with A. r u f i c r u s in e x a c tl y the same kind of experimental design and under a s i m i l a r s e t of physical condi­ tions. However, p a r a s i t i s m r a t e s of A. r u f i c r u s (Table 12) were much poorer than t h e r a t e s observed f o r A. m i l i t a r i s (Table 11). No p a r a s i t i s m occurred a t d e n s i t i e s equal to or below 10 armyworm la r v a e per cage, when e i t h e r 5 o r 10 females per cage were used. The p a r a s i t o i d maintained i t s p refe ren c e o f 2nd i n s t a r la r v a e and did not p a r a s i t i z e 4th i n s t a r s d e s p i t e t h e i r l a r g e r s i z e and g r e a t e r chance of being disc overed. Mean p e rc en t p a r a s i t i s m by A. m i l i t a r i s females a s s o c i a t e d with every number o f hosts su p p lied i s given in Table 13 f o r both q u a n t i t i e s of p a r a s i t o i d s employed; the corresponding treatm ent combination means f o r A. r u f i c r u s are pre sented in Table 14. Standard e r r o r s o f the mean have been included in a l l t a b l e s to show the extent of variation. P r i o r to any s t a t i s t i c a l tr e a tm e n t, an inverse sin e (angular) tr an sform ation was a p p lie d to a l l measured p ercent p a r a s i t i s m r a t e s , as many a t t a c k r a t e s were zero. This tr ansfo rm atio n helped a d j u s t f o r 65 Table 13. Parasitoids Released Average P ercen t o f Armyworms P a r a s itiz e d by A. m i l i t a r i s Females R eleased in a Cage w ith a 1 .9 5 Basal Area D uring an 8 h r P eriod Hosts Exposed Percent P a r a s i t i z e d by I n s t a r --------------------------------------------------------Second Third Fourth o o' 0.0 0.0 0.0 0.0 8.3 ± 8.3 8.3 4.2 ± 4.2 11.7 ± 7.9 3.3 ± 2.1 5.9 ± 2.4 16.8 ± 4.9 4.2 ± 2.0 40 10.4 ± 3.5 12.2 ± 4.1 8.8 ± 4.8 1 16.7 ± 16.7 0.0 0.0 2 16.7 ± 10.5 25.0 ± 11.2 33.3 ± 16.7 4 16.7 ± 8.3 10 13.3 ± 20 40 1 2 4 0.0 16.7 ± 10 8.3 ± 3.1 20 5.3 4.2 ± 4.1 9.5 21.7 ± 12.5 23.3 ± 9.9 19.2 ± 5.0 26.4 ± 5.7 7.5 ± 2.5 12.3 ± 3.6 19.2 ± 6.1 10.7 ± 3.6 aMean + S .E . o f 6 r e p lic a t e s . 8.3 ± 66 Table 14. Average Percent of Armyworms P a r a s i t i z e d by A. r u f i c r u s Females Released in a Cage with a 1.95 nr Basal Area During an 8 hr Period Percent P a r a s i t i z e d by I n s t a r 3 Parasitoids Released Hosts Exposed Second Third Fourth 5 40 0.0 0.0 0.0 10 1 0.0 0.0 0.0 2 0.0 o • o 0.0 4 0.0 0.0 0.0 10 0.0 0.0 0.0 20 1.9 ± 1.9 0.0 0.0 40 3.9 ± 2.6 aMean ± S .E . o f 6 r e p lic a t e s . 1.3 ± .9 0.0 67 v a r i a b i l i t y and norm aliz ation of th e d i s t r i b u t i o n (Steel and Torrie 1980). A comparison was f i r s t made between p a r a s i t o i d a t t a c k r a t e s . Only the impact on 2nd, 3rd and 4th i n s t a r larv a e a t the h ig h es t host and p a r a s i t o i d d e n s i t i e s (40 h o s t s ; 10 p a r a s i t o i d s ) was t e s t e d since f o r ho st d e n s i t i e s lower than 40 s i g n i f i c a n t d i f f e r e n c e s were obvious. Results o f the tw o - f a c to r a n a l y s i s o f variance comparing the a t t a c k e f f i c i e n c y c h a r a c t e r i s t i c s of each species are shown in Table 15. The following can be concluded: (1) a g r e a t d i f f e r e n c e in the searching performance e x i s t s between t h e two p a r a s i t o i d species ( f a c t o r A). At a d e n s i ty of 40 armyworms per cage, p a r a s i t is m r a t e s were found to be highly s i g n i f i c a n t , fav o rin g the na tiv e A. m i l i t a r i s over the introduced spe cie s (F = 23; P = .0 1 ); (2) t h e r e was no s i g n i f i c a n t d i f f e r e n c e in p a r a s i t i s m r a t e among the t h r e e armyworm i n s t a r s ( f a c t o r B) used; f i n a l l y , (3) no s i g n i f i c a n t i n t e r a c t i o n occurred between f a c t o r s . Analysis o f variance was conducted f o r A. m i l i t a r i s a lo n e , to compare p ercen t p a r a s i t i s m a t the two p a r a s i t o i d d e n sity l e v e l s (5 and 10). Comparisons were made only f o r the t h r e e higher host d e n s i t i e s (10, 20 and 40) s i n c e , f o r the lower host numbers t e s t e d , d i f f e r e n c e s were somewhat confounded. This was l a r g e l y due to the low number of h osts supplied and r e p l i c a t e s used. A summary of t h i s t h r e e - f a c t o r a n a l y s i s i s provided in Table 16. P a r a s itis m r a t e (% ) r e s u l t i n g from exposure o f armyworm larv a e to p a r a s i t o i d d e n s i t i e s ( f a c t o r A) o f 5 or 10 d i f f e r e d s i g n i f i c a n t l y (F = 8 .091). When the number of p a r a s i t o i d s was doubled, p a r a s i t i z a t i o n increased s i g n i f i ­ c a n t l y (P = .01). Again, a marked d i f f e r e n c e in p a r a s i t i s m incidence between armyworm l a r v a l i n s t a r s ( f a c t o r C) occurred (F = 3.261). 68 Table 15. Two-factor Analysis of Variance of P a r a s i ti s m Rates by A. m i l i t a r i s and A. r u f i c r u s Searching f o r Three D i f f e r e n t I n s t a r s o f the Host, P_. unipuncta (A = P a r a s i t o i d Species; B = Host I n s t a r ) DF SS MS F AB 2 .86267E+02 .43133E+02 .632 A 1 . 15686E+04 . 15686E+04 22.983^ B 2 •12355E+03 .61776E+02 .905 ERROR 30 .20475E+04 •68249E+02 TOTAL 35 .38259E+04 Source ♦ ♦ S i g n i f ic a n t a t P = .01 69 Table 16. Thr ee-Factor Analysis of Variance o f P a r a s i ti s m Rates by 5 and 10 Females of A. m i l i t a r i s Searching f o r Three D i f f e r e n t I n s t a r s of the Host, £ . unipuncta (A = P a r a s i t o i d Density; B = Host Density; C = Host Instar) DF SS MS F ABC 4 •32501E+03 .81253E+02 .637 AB 2 . 11892E+03 . 59459E+02 .466 AC 2 . 12009E+02 .60043E+01 .047 A 1 . 10316E+04 . 10316E+04 8.091^ BC 4 . 43030E+03 . 10757E+03 .844 B 2 .27493E+02 . 13747E+02 .108 C 2 .83144E+03 .41572E+03 3.261^ ERROR 90 .11475E+05 .12750E+03 TOTAL 107 .14252E+05 Source ♦ ♦ S i g n i f ic a n t a t P = .01 ♦ S i g n i f i c a n t a t P = .05 70 However, no s i g n i f i c a n t d i f f e r e n c e occurred between the t h r e e host d e n s i ty l e v e l s ( f a c t o r B). Also, a t the t e s t l e v e l s chosen, no s i g n i f i c a n t i n t e r a c t i o n s were e v id e n t among a l l t h r e e f a c t o r s i n v e s t i g a t e d ( p a r a s i t o i d d e n s i t y , ho st d e n s i t y , and ho st i n s t a r ) . For c lo s e v e r i f i c a t i o n of the second co nclu sion , above, Bonferroni procedure f o r non-orthogonal c o n t r a s t s (Gill 1978a) was u t i l i z e d to compare p e rc e n t i n s t a r tr e a tm e n t combination means. The r e s u l t of t h i s t e s t shows t h a t only 3rd and 4th i n s t a r s were in f a c t d i f f e r ­ e n t l y a f f e c t e d by p a r a s i t i s m caused by A. m i l i t a r i s (a = .0 5). D i f f e r e n t i a l p a r a s i t i s m was unimportant f o r comparisons involving 2nd instars. Secondary E f fe c t s o f P a r a s i t i z a t i o n Following a procedure s i m i l a r to t h a t used in th e v ial t e s t s , upon completion of a cage t e s t , a l l armyworm l a r v a e found were i s o l a t e d and rea red f o r p a r a s i t o i d emergence. The r e a r i n g r e s u l t s from exposure t o A. m i l i t a r i s a re shown in Tables 17 and 18 while Table 19 summarizes the data f o r A. r u f i c r u s . All t h r e e t a b l e s have been organized according to numbers o f p a r a s i t o i d s l i b e r a t e d in the cages. Data recorded f o r the vario us c a t e g o r i e s (h o st e f f e c t i v e p a r a s i t i s m , unknown-caused d e a t h s , pupation, and l o s s e s ) are in d i r e c t correspondence with h o st d e n s i t i e s and i n s t a r s used. Regarding e f f e c t i v e p a r a s i t i s m (columns 3 and 4 ) , i t i s c l e a r from the cumulative frequency ( t o t a l ) column t h a t an in cre ase in both h ost and p a r a s i t o i d d e n s i ty r e s u l t e d in a g r e a t e r r a t e of a t t a c k by both p a r a s i t o i d s . The u ncle ar de trimental e f f e c t s of o v i p o s i ti o n and p a r a s i t i s m , l a r g e l y included in deaths due to unknown causes (columns 5 and 6 ) , become more e v id e n t as h o st d e n s i ty i n c r e a s e s . Avoidance of Table 17. Subsequent History of P. unipuncta Larvae Exposed a t Various Densi ties to 5 A. m i l i t a r i s Females in Cages 1.95 in2 in Surface Area f o r 8 Hours3 Suc cessfully P a r a s i ti z e d Freq. Tot. Host Density Host Instar 1 2nd 3rd 4th 0 0 0 2 2nd 3rd 4th 0 0 1 4 2nd 3rd 4th 0 4 1 10 2nd 3rd 4th 5 7 2 20 2nd 3rd 4th 7 20 5 40 2nd 3rd 4th 25 29 21 Unexplained Deaths Freq. Tot. 0 0 0 0 1 0 1 18 62 54 48 54 32 103 86 101 34 15 17 24 0 2 1 1 290 198 191 192 56 0 0 0 0 156 10 8 13 13 0 0 0 0 24 18 20 5 14 0 0 0 0 34 1 1 5 4 Lost Larvae Freq. Tot. 0 0 0 12 11 11 0 2 3 5 aSix r e p lic a te s per t e s t . 6 6 6 0 0 75 Surviving Larvae Freq. Tot. 4 2 3 3 581 8 Table 18. Subsequent History of P. unipuncta Larvae Exposed a t Various Densities to 10 A. m i l i t a r i s Females in Cages 1.95 n ? in Surface Area f o r 8 Hours9 Successfully P a r a s i ti z e d Freq. Tot. Host Density Host Instar 1 2nd 3rd 4th 1 0 0 2 2nd 3rd 4th 2 3 4 4 2nd 3rd 4th 4 2 1 10 2nd 3rd 4th 8 13 14 Unexplained Deaths Freq. Tot. 0 0 0 0 3 0 9 40 2nd 3rd 4th 29 46 24 aSix r e p lic a te s p er t e s t . 141 18 0 4 2 0 274 199 184 183 42 0 0 0 0 87 78 109 9 9 24 99 60 4 62 0 0 0 0 51 45 45 7 9 2 0 0 0 0 24 5 1 2 1 35 22 31 9 17 19 19 22 1 3 1 Lost Larvae Freq. Tot. 0 0 0 10 6 8 3 7 2nd 3rd 4th 5 6 6 0 0 20 Surviving Larvae Freq. Tot. 6 3 1 9 566 13 Table 19. Subsequent History of P. unipuncta Larvae Exposed a t Various Densities to 10 A. r u f i c r u s Females in Cages 1.95 w - in Surface Area fo r 8 hours3 Successfully P a r a s i ti z e d Freq. Tot. Host Density Host Instar 1 2nd 3rd 4th 0 0 0 2 2nd 3rd 4th 0 0 0 4 2nd 3rd 4th 0 0 0 10 2nd 3rd 4th 0 0 0 20 2nd 3rd 4th 2 0 0 40 2nd 3rd 4th Unexplained Deaths Freq. Tot. 0 1 0 0 0 171 6 0 3 1 0 348 220 234 234 14 0 0 0 0 109 119 120 6 3 5 12 0 0 0 71 9 2 0 35 56 59 56 6 0 0 0 0 0 0 23 24 24 1 0 9 3 0 is 1 4 1 4 Lost Larvae Freq. Tot. 0 0 0 11 12 12 1 0 0 0 aS ix r e p lic a te s per t e s t . 6 6 6 0 0 0 0 Surviving Larvae Freq. Tot. 4 5 0 1 688 6 74 p a r a s i t i s m , expressed in terms o f normal pupation (columns 7 and 8 ) , was most common and followed a general tr en d s i m i l a r to t h a t found in the confined t e s t s (Tables 6 and 7 ) . The number of h o sts which could not be recovered from the cages a f t e r t e s t s were completed ( l a s t two columns) was minimal. In only 4 of 54 t e s t s did host l o s s e s exceed 10% of the number l i b e r a t e d . Although t h i s low l o s s r a t e was thought to be i r r e l e v a n t , the number of armyworm la r v a e l o s t was s u b t r a c t e d from those r e l e a s e d befo re p a r a s i t i s m v a lu e s , o t h e r d e a t h s , and pupation were computed. In t h i s way, a l l da ta disc usse d herein were c a l c u l a t e d on the b a s i s o f l a r v a e a c t u a l l y recovered and r e a red f o r p a r a s i t o i d emergence. As in the confined t e s t s , s u p e r p a r a s i t is m as well as o th er adverse e f f e c t s derived from p a r a s i t o i d o v i p o s i t i o n may have accounted f o r some o f th e unexplainable d e a th s. Data in Table 8 suggest t h a t the number o f h o s t s which were found and in which eggs were deposited may be g r e a t e r than p re v i o u s ly shown. T herefo re, i t seems lo g ic a l t h a t new fu n c tio n a l response valu es should be c a l c u l a t e d which take i n to account t h i s e xac erb a ting p a r a s i t i s m effect. They are thought to be a more a c c u ra t e r e p r e s e n t a t i o n o f the r a t e of host encounters by searching females. This number can be obtained by adding to the data prev io u sly shown (Tables 10-14) the number o f p a r a s i t i s m - a s s o c i a t e d deaths oc cu rrin g among those la r v a e dying from unknown cause s. For the computations, a 20% na tu ra l m o r t a l i t y value (this" i s g r e a t e r than the 14% mean n a tu r a l m o r t a l i t y observed in e a r l i e r t e s t s ; see page 45) was su b tr a c te d from the unexplained deaths be fore a l l m o r t a l i t y data were combined. g r e a t e r response i s expressed in Table 20 (see Table 10 f o r The 75 Table 20. Parasitoids Released Probable Number of Armyworms Found by A. m i l i t a r i s and A. r u f i c r u s Females in Cage Experiments Taking into Account Secondary E f fe c ts o f P a r a s i t i z a t i o n 3 Hosts Exposed 1 2 Hosts Found by________ A. m i l i t a r i s A. r u f i c r u s (3.0 .1 + .1 - .5 ± 1.2 + .2 - .3 - 3.3 1 6.7 + .7 - .7 1.2 ± .1 + .6 + .1 0.0 .2 0.0 .2 0.0 10 .6 + 2.1 + .6 .4 ± .1 20 4.2 + .7 .4 ± .2 40 7.4 ± 1.2 1.3 ± .5 4 10 20 40 1 2 4 .3 aMean ± S.E. of 18 r e p l i c a t e s (6 r e p s , each using 2nd, 3rd and 4th i n s t a r s ) . 76 comparison); i t r e p r e s e n t s the average number o f host s probably discovered and stung by females of both s p e c i e s . Combined m o r t a l i t y r a t e s recorded f o r each s p e c i f i c i n s t a r t e s t e d are given in Table 21 (A. m i l i t a r i s ) and in Table 22 (A. r u f i c r u s ) (see Tables 11 and 12 f o r comparison). Some remarkable a d a p t a t i o n s lin k i n g A. m i l i t a r i s to i t s n a tu ra l h o s t , _P. u n ip u ncta , were observed during t h i s study. For example, A. m i l i t a r i s females were f r e q u e n t l y observed hovering over the p l a n t s occupied by artnyworm l a r v a e . As the experiments were dism an tled , they were o f te n seen s i t t i n g on the p l a n t s and sometimes on th e p l a s t i c r in g enclo sin g a group o f p l a n t s . Females of A. r u f i c r u s u s u a l ly wandered about under the c ag e ’s top screen or simply flew above the plants. Unlike A. r u f i c r u s , the n a tiv e p a r a s i t o i d seemed to " p a t r o l " the a r e a s surrounded by the r i n g s , looking d i l i g e n t l y f o r p rosp ectiv e h o s t s . However, no attempt was made to q u a n ti f y the time spent by the wasps on or around the p l a n t s being fed upon by the host l a r v a e . The r e s u l t s of the cage t e s t s i n d i c a t e t h a t A. r u f i c r u s i s poorer in i t s searching and p a r a s i t i z i n g a b i l i t i e s than A. m i l i t a r i s ; however, on P a k istan i h osts the rev erse i s c e r t a i n l y a p o s s i b i l i t y . The cage s i t u a t i o n was probably a nice r e p r e s e n t a t i o n o f what might occur in the f i e l d ( a t l e a s t f o r A. m i l i t a r i s ) , c o n sid ering the number of armyworms which were p a r a s i t i z e d . In order to have a workable system ( e s p e c i a l l y f o r re cov ery ), some f e a t u r e s ( e . g . , p l a n t type and age, and presence of b a r r i e r s to r e s t r i c t armyworm movement) were u n n a tu r a l, but these extraneous components did not appear to be i n h i b i t o r y to e i t h e r s p e c i e s ' searching behavior. I t i s p o s s i b l e , of 77 Table 21. Probable Number of Armyworms Found by A. m i l i t a r i s Females in Cage Experiments Taking i n t o Account Secondary E f fe c ts of Parasitization Parasitoids Released Hosts Exposed 5 1 2 0.0 0.0 .1 ± .1 .2 ± .2 4 0.0 .9 ± .3 .6 ± .3 10 Second Hosts Found by I n s t a r 3 Third Fourth 0.0 0.0 10 1.0 ± .4 1.8 ± .9 .9 ± .3 20 2.2 ± .7 5.1 ± 1.5 2.6 ± .9 40 6.2 ± 1.2 7.1 ± 1.2 6.7 ± 1.6 0.0 0.0 1 .2 ± .2 2 .3 ± .2 .9 ± .2 .7 ± .2 4 .8 ± .3 .7 ± .3 .3 ± .2 10 1.5 ± .9 2.4 ± 1.2 2.5 ± 1.0 20 4.6 ± 1.0 6 .4 ± 1.3 1.8 ± 40 6.0 ± 1.7 8.9 ± 2.6 7.2 ± 1.9 aMean ± S .E . o f 6 r e p lic a t e s . .4 78 Tab le 22. P robable Number o f Armyworms Found by A. r u f ic r u s Females in Cage Experim ents Taking in to Account Secondary E ffe c ts o f P a r a s it iz a tio n Parasitoids Released Hosts Exposed 5 40 10 1 Hosts Found by I n s t a r a Second Third Fourth 2.0 ± .7 0.0 .9 ± .5 .7 ± 0.0 0.0 2 .1 ± .1 0.0 0.0 4 .1 ± .1 0.0 0.0 10 .5 ± .3 20 1.1 ± .6 40 2.3 ± 1.5 aMean ± S.E. o f 6 r e p l i c a t e s . .1 ± .1 0.0 .9 ± .5 ± .2 .2 0.0 .6 .7 ± .4 79 course, t h a t A. r u f i c r u s may have responded more abnormally than A. m ilitaris. Although l i t t l e i s known about armyworm d i s p e r s i o n , i t is believed t h a t a clumped d i s t r i b u t i o n would sim ulate more c l o s e l y i t s fie ld distribution. Although the host r e l e a s e was random, the fi n a l d i s t r i b u t i o n often r e f l e c t e d varying degrees o f aggre gation. This was due t o the f a c t t h a t several la r v a e were placed in the same space surrounded by the r i n g , more so when a l a r g e number of la r v a e had to be used. Time o f exposure employed in fu n ctio n al response and s i m il a r s t u d i e s v a r i e s co n sid era b ly ( s e e , f o r example, Hassell 1978). After having experimented with 24 and 12 h r , i t was believed t h a t an 8-hr exposure would be j u s t as a p p r o p r i a t e , since within t h i s s h o r t e r period the p a r a s i t o i d response could be measured even f o r very low h ost d e n s i t i e s ( e . g . , a t one h o s t , f o r A. m i l i t a r i s ) . A relatively sh o r t exposure time may a l s o have avoided e f f e c t s due to e a r l y p a r a s i t o i d m o r t a l i t y and s u p e r p a r a s i t is m . Indeed, p a r a s i t o i d s are l e s s l i k e l y to survive t o the end of long exposu res , and i t i s p r a c t i c a l l y impossible to f in d and hence record the number o f females a l i v e a f t e r each t e s t . Also, t h e r e are not many models in co rp o ra tin g the e f f e c t s of competition (Hassell 1978). Thus, i t i s un fo rtu n ate t h a t because of time l i m i t a t i o n s a combination of both p a r a s i t o i d s ' responses could not be t e s t e d . Future resea rch t h e r e f o r e should explore the e f f e c t s of t h i s r e l a t i o n s h i p by t e s t i n g the two sp ecies a t the same time with the h o st. 80 P a r a s ito id Reproduction The number o f eggs t h a t Apanteles sp e c ie s are capable of d e p o s i ti n g i s u s u a l ly l a r g e . Their fec u n d ity depends l a r g e l y on the i n t r i n s i c rep ro du c tive c a p a c i ty o f each s p e c i e s , but o v i p o s i ti o n r a t e s a re markedly influ enced by host population d e n s i ty as w e l l , the number of p a r a s i t o i d progeny being p a r t l y determined by how many h o sts the p a r a s i t o i d can f i n d . by the following da ta . Some o f th ese r e l a t i o n s h i p s are shown Several measures o f p a r a s i t i s m per u n i t time such as the number o f h o sts p a r a s i t i z e d , the number of p a r a s i t o i d eggs l a i d , the number o f eggs l a i d per ho st exposed, numbers o f female and male progeny, e t c . a re describ ed and analyzed. The data included in t h i s se c t i o n come from the two l a b o r a t o r y t e s t s i t u a t i o n s e a r l i e r d e scrib e d where armyworm h o s t s were e i t h e r i s o l a t e d si n g l y with one female wasp of each sp e cie s w ith in a standard v ial f o r 24 hr ( " v ial t e s t s " ) , o r were r e l e a s e d on b a rl e y p l a n t s grown in f l a t s and enclosed in a screen cage with a known number of females f o r an 8 - h r period ("cage e x p erim e n ts" ). Addi­ t i o n a l l y , r eal f i e l d data f o r A. m i l i t a r i s a re a ls o compared with the r e s u l t s obtained in the l a b o r a t o r y . In general, sample s i z e s f o r drawing co n clu sio n s about the reproductio n o f A. r u f i c r u s were by n e c e s s i t y sm aller. Before d isc u ssio n of the o b se rvatio ns a c l e a r d i s t i n c t i o n must be made between the two l a b o r a t o r y d esig n s. In the small v i a l , the p a r a s i t o i d was more l i k e l y to f i n d the h o st because of th e c lo s e confinement. In the cage, however, a p a r a s i t o i d c l e a r l y had g r e a t e r d i f f i c u l t f i n d in g a host as i t had to search e x t e n s i v e l y f o r i t . 81 Information r e l a t e d to p a r a s i t i s m by A. m i l i t a r i s and showing mean numbers of progeny emerged from 2nd-, 3rd- and 4 t h - s t a g e host larvae i s pre sented in Tables 23, 24, and 25, r e s p e c t i v e l y . S i m i la r ly , f ec u n d ity and progeny production data f o r A. r u f i c r u s are given in Tables 26 to 28; they r e s u l t from p a r a s i t i s m under the same confined or simulated f i e l d c o n d i t i o n s . The confined t e s t f i g u r e s in a l l t a b l e s were computed from data of experiments disc ussed e a r l i e r (see page 45), involving mated females of varying ages, whereas the cage study data r e f e r only t o p a r a s i t i s m information c o l l e c t e d where the host d e n s i t y was 40 and the p a r a s i t o i d d e n sity was 10 (see page 57). In both c a s e s , averages computed from counts of cocoon numbers produced from a s i n g l e l a r v a were used to est im ate the number o f eggs l a i d per p a r a s i t i z e d arrnyworm per i n s t a r , under the c o nd itio ns mentioned. Actual o v i p o s i ti o n r a t e s could be higher sin c e a l l eggs l a i d would not n e c e s s a r i l y complete development. In h i s account of the biology of A. m i l i t a r i s , Tower (1915) included only a few notes on mating and o v i p o s i t i o n . Calkins and S u t t e r (1976) r e p o r t e d t h a t 3 to 226 a d u l t A. m i l i t a r i s emerged per host with an average o f 71 p a r a s i t o i d s emerging from 3rd, 22 from 4 t h , and 81 from 5th i n s t a r h o s t s . Second i n s t a r s would not p a r a s i t i z e d . Under s i m i l a r c o n d it i o n s , t h i s study found an average of 79, 111 and 82 a d u l t A. m i l i t a r i s emerging from s i n g l e 2nd, 3rd and 4th i n s t a r l a r v a e , r e s p e c t i v e l y . For A. r u f i c r u s , averages were sm aller with 57, 43 and 39 a d u l t s emerging from 2nd, 3rd and 4th in s ta r larvae, respectively. Calkins and S u t t e r (1976) a ls o noted t h a t with surplus host s a v a i l a b l e the mean number of h o sts p a r a s i t i z e d by one female A. 82 T ab le 2 3 . Average Number o f Progeny Produced by Exposure o f 2nd In s t a r Armyworm Larvae to A. m i l i t a r i s Observation (Numbers/Percent) Hosts P a r a s i t i z e d (n) Vial Tests 31 Cage Experiments 29 Average Number3 of Cocoons Produced/Host 94.0 ± 10.1 26.2 ± 3.1 Adults Emerged/Host 78.6 ± 9.6 20.4 ± 2.2 Female Off spring/Host 28.3 ± 4.3 55.6 ± 4.0 Male Offspring/Host 71.7 ± 4.3 44.4 ± 4.0 81.4 ± 2 .8 81.3 ± 1.9 Average Percentage3 of Average Emergence Rate3 { %) Sex Ratio o f Progeny ($/<*■) .4 aMean ± S .E . (n = no. o f p a r a s it iz e d host la r v a e ) . 1.3 83 Table 24. Average Number o f Progeny Produced by Exposure o f 3rd In s t a r Armyworm Larvae to A. m i l I t a r i s Vial Tests Cage Experiments 38 46 Cocoons Produced/Host 132.2 ± 11.3 35.1 ± 3.2 Adults Emerged/Host 111.2 ± 9 .8 27.4 ± 2.5 Female Offspring/Hos t 18.6 ± 3.3 36.4 ± 3.5 Male Offspring/Host 81.4 ± 3.3 63.6 ± 3.5 Observation (Numbers/Percent) Hosts P a r a s i t i z e d (n) Average Number3 of Average Percentage3 of Average Emergence Rate3 ( %) Sex Ratio o f Progeny (?/cf) 82.8 ± 2.5 .2 aMean ± S .E . (n = no. o f p a r a s itiz e d host la r v a e ) . 81.1 ± 2.3 .6 84 T ab le 25. Average Number o f Progeny Produced by Exposure o f 4th In s t a r Arrnyworm Larvae to A. m il i t a r i s Observation (Numbers/Percent) Hosts P a r a s i t i z e d (n) Vial Tes ts Cage Experiments 42 24 Average Number3 of 110.5 ± 8.0 47.4 ± 3.8 81.6 ± 6.4 33.9 ± 2.9 Female Offspring/Host 16.8 ± 3.3 39.1 ± 6.7 Male Offspring/Host 83.2 ± 3.3 60.9 ± 6.7 74.4 ± 2.1 71.9 ± 3.6 Cocoons Produced/Host Adults Emerged/Host Average Percentage3 o f Average Emergence Rate3 ( %) Sex Ratio o f Progeny ( s / c r ) .2 aMean ± S .E . (n = no. o f p a r a s itiz e d h ost la r v a e ) . .6 85 Table 26. Average Number o f Progeny Produced by Exposure o f 2nd In s ta r Arrnyworm Larvae to A. r u f ic r u s Observation (Numbers/Percent) Hosts P a r a s i t i z e d (n) Vial Tes ts Cage Experiments 35 9 Average Number3 of Cocoons Produced/Host 66.9 ± 6.9 17.6 ± 1.7 Adults Emerged/Host 56.9 ± 5.9 15.7 ± 1.5 Female Offspring/Host 47.6 ± 3.2 41.7 ± 6.1 Male Offspring/Host 52,4 ± 3.2 58.3 ± 6.1 87.1 ± 2.0 89.3 ± 2.4 Average Percentage3 of Average Emergence Rate3 ( %) Sex Ratio of Progeny (?/<*•) .9 aMean ± S .E . (n = no. o f p a r a s itiz e d host la r v a e ) . .7 86 Tab le 2 7. Average Number o f Progeny Produced by Exposure o f 3rd In s t a r Armyworm Larvae to A. r u f ic r u s Observation (Numbers/Percent) Hosts P a r a s i t i z e d (n) Vial T ests Cage Experiments 32 3 Average Number3 of Cocoons Produced/Host 46.6 ± 5.1 26.3 ± 6.7 Adults Emerged/Host 42.6 ± 4.9 21.7 ± 5.4 Female Offspring/Host 53.4 ± 3.9 57.6 ± 7.6 Male Offs pring/Hos t 46.6 ± 3.9 42.4 ± 7.6 Average Emergence Rate3 (%) 91.1 ± 1.6 82.7 ± 2.0 Sex Ratio of Progeny (?/<*•) 1.1 Average Percentage3 of aMean ± S .E . (n = no. o f p a r a s it iz e d host la r v a e ) . 1.4 87 T ab le 28. Average Number o f Progeny Produced by Exposure o f 4th In s t a r Armyworm Larvae to A. r u f ic r u s Observation (Numbers/Percent) Hosts P a r a s i t i z e d (n) Vial T ests Cage Experiments 6 0 Average Number3 of Cocoons Produced/Host 46.2 ± 13.6 - Adults Emerged/Host 38.5 ± 10.2 - Female Offspring/Host 38.1 ± 10.4 - Male Offspring/Host 61.9 ± 10.4 - 87.9 ± - Average Percentage3 of Average Emergence Rate3 (%) Sex Ratio o f Progeny (?/<*•) 3.8 .6 aMean ± S .E . (n = no. o f p a r a s it iz e d h o st la r v a e ) . - 88 m i l i t a r i s was 9, and the t o t a l average progeny per female wasp was 512 (4-hr exposure period in both c a s e s ) . They co nsider these values low and suggested t h a t perhaps A. m i l i t a r i s would o v i p o s i t more eggs i f allowed to do so over several days. obse rvation f o r A. r u f i c r u s . Hafez (1947) made a s i m i l a r He found t h a t the average number of Aqro tis larvae p a r a s i t i z e d by a s i n g l e Apanteles female was about 5 (range 1-10) with an average number of progeny per female of 216 (range 13-490). The values measured by these i n v e s t i g a t o r s were based on the number o f a d u l t p a r a s i t o i d s emerged. The number of cocoons spun by the newly-emerged la r v a e i s , however, a b e t t e r , although s t i l l low, estim ate f o r eggs l a i d , as a d u l t emergence is never 100% e f f e c t i v e . A g r e a t deal o f l a r v a l and pupal m o r t a l i t y normally occurs in the cocoon, as can be seen from the r a t e s of emergence computed f o r both species (Tables 23-28). Egg o r l a r v a l m o r t a l i t y a ls o must occur within the ho st befor e la r v a e spin cocoons. The p r e s e n t study a l s o shows t h a t the average number of cocoons produced (here used to e s tim a te both eggs l a i d and emerged p a r a s i t o i d larva e per ho st) and p a r a s i t o i d s emerged were both s i g n i f i c a n t l y lower from host s a ttac k ed in the cages than from those confined in vials. I t appeared t h a t the need to search f o r more s p a r s e ly d i s t r i ­ buted h o sts in the cages probably accounted f o r the lower p a r a s i t is m r a t e s of both s p e c i e s . When host and p a r a s i t o i d were held in clo se confinement the r a t e of p a r a s i t i s m per u n i t time tended to increase and, as a consequence, the p a r a s i t o i d o v ip o s ite d more o f t e n , leaving a g r e a t e r number o f progeny. Simulated f i e l d c o n d i t i o n s , t h u s, r e s u l t e d in a lower o v i p o s i ti o n response from both s p e c i e s , i r r e s ­ p e c t iv e of host i n s t a r a tt a c k e d . Production of la r v a e and a d u l t s from 89 each i n s t a r was c o n siderably l e s s f o r A. r u f i c r u s than f o r A. m ilitaris. I t should be noted, however, t h a t sample s i z e s a s s o c i a t e d with the imported Apanteles were in general much sm aller. Fourth i n s t a r c a t e r p i l l a r s o f A. r u f i c r u s were not used because the p a r a s i t o i d f a i l e d to s u c c e s s f u l l y a t t a c k them in the cage. Sample s i z e s ( n ) , which a re the same as the t o t a l armyworms found p a r a s i ­ t i z e d f o r each i n s t a r , a re of comparable magnitude among 2nd and 3rd i n s t a r s , but a re probably too small to warrant any v a li d conclusions from the cage t e s t s conducted with A. r u f i c r u s . Fourth i n s t a r larvae were not r e a d i l y a tt a c k e d by A. r u f i c r u s under e i t h e r experimental setup used. Tables 23 through 28 a ls o include average percentages of female and male o f f s p r i n g as counted from each p a r a s i t i z e d group. e a s i l y be manipulated to produce d e s i r e d sex r a t i o s . These can Among A. r u f i c r u s , female and male progeny approximated a 1:1 r a t i o more c l o s e l y than f o r A. m i l i t a r i s whose brood, in la b o r a to r y t e s t s , seem to include a smaller pro portio n of females. These data are in general thought to have some b i o lo g ic a l s i g n i f i c a n c e as they r e p r e s e n t the number of larvae and a d u l t p a r a s i t o i d s l i k e l y to emerge and make up the next g e neratio n. A. r u f i c r u s produces, on the average, fewer o f f s p r i n g (eggs, la r v a e and a d u l t s ) than A. m i l i t a r i s does. The higher reproductiv e r a t e s of A. m i l i t a r i s with a wider range o f host i n s t a r s are indeed a c l e a r i n d ic a t i o n of i t s g r e a t e r reproductive p o t e n t i a l when a tt a c k i n g £ . u nipuncta. The higher f e c u n d i ty , combined with o ther i n t r i n s i c c h a r a c t e r i s t i c s , i s l i k e l y to favor the n a tiv e Apanteles in a more n atu ral s e t t i n g , and indeed t h i s seems to be the case as A. r u f i c r u s 90 was not recovered in subsequent y e a r s from the f i e l d a f t e r r e l e a s e . Even i f the longer l i f e span o f A. r u f i c r u s i s considered (ca. two times t h a t o f A. m i l i t a r i s ) , t o t a l fecundity of A. r u f i c r u s i s very low compared to t h a t o f A. m i l i t a r i s . To make these l a b o r a t o r y comparisons more meaningful, f i e l d p a r a s i t i s m data by A. m i l i t a r i s a re a ls o provided (Table 29). The parameters are s i m i l a r to those discussed above and were c o l l e c t e d among non-outbreak arn\yworm populations feeding on n o - t i l l corn. When compared with d a ta in Tables 23-25, both f i e l d and cage Fj progeny means were co n sid era bly lower than those produced under a s t r i c t l y confined s i t u a t i o n . This i n c r e a s e s the p r o b a b i l i t y t h a t confined Apanteles females make repeated host a t t a c k s , o v i p o s i ti n g several times in a s i n g l e i n d i v i d u a l , e s p e c i a l l y i f confinement i s imposed. This may, in t u r n , cause su p e r p a r a s i t is m to occur a t a g r e a t e r r a t e . Despite the lack o f f i e l d data f o r A. r u f i c r u s , a s i m i l a r behavior seems to be p l a u s i b l e , judging from i t s o v i p o s i ti o n p a t t e r n (Tables 25-28). I t may be of i n t e r e s t to note t h a t the data given in Table 29 a re complementary to those in Table 1 wherein armyworm da ta on f i e l d p a r a s i t i s m by A. m i l i t a r i s were pres ented. In the p a s t , s t u d i e s have suggested a p o s s ib le c o r r e l a t i o n between host s i z e and number o f p a r a s i t o i d eggs l a i d (Vinson and Iwantsch 1980). In t h i s study, t h i s r e l a t i o n s h i p was not apparent, i f the whole i n s t a r range was considered. To i l l u s t r a t e t h i s , Table 30 i s provided where average production o f cocoons i s s p e c i f i e d by l a r v a l i n s t a r s and numbers of i n d iv i d u a ls k i l l e d . Although the number of samples was not l a r g e , one p o in t seems noteworthy. There i s Table 29. Average Number o f A. m i l i t a r i s Emerging from Field-S am pled Armyworm Larvae9 Field Sampled & Colle ction Date*3 Observation (Numbers/Percent) I 6/17/80 II 6/24/80 III 7/12/80 23 32 68 Hosts P a r a s i t i z e d (n) Average Number0 of Cocoons Produced/Host 53.0 ± 6.7 39.1 ± 3.7 60.5 ± 3.7 Adults Emerged/Host 48.7 ± 6.1 36.9 ± 3.5 34.7 ± 3.0 Female Offspring/Host 65.6 ± 2.4 56.2 ± 2.9 60.9 ± 1.4 Male Offspring/Host 34.4 ± 2.4 43.8 ± 2.9 39.1 ± 1.4 93.3 ± 1.9 94.9 ± 1.2 53.5 ± 2.2 1.9 1.3 1.6 Average Percentage0 of Average Emergence Rate (%) Sex Ratio of Progeny (?/<*) aLate i n s t a r s most prev alen t in samples. ^Five samples per f i e l d ; 25 larvae per sample. Mean ± S.E. (n = no. of p a r a s i t i z e d host l a r v a e ) . Table 3 0. Average Number o f Cocoons Produced from Armyworms P a ra s itiz e d (AP) When Confined in a V ia l W ith One Female A. m i l i t a r i s f o r 24 Hours Hosts P a r a s i t i z e d & Cocoons Produced/Larva,a Armyworm Instar Test 1 Test 2 Test 3 S.E. AP X + S.E. 2 83.5 ± 37.5 5 89.0 ± 18.7 99.7 ± 15.0 7 92.6 ± 23.8 12 89.3 ± 17.7 13 123.9 ± 14.9 12 124.2 ± 23.4 13 147.8 ± 21.0 4th 13 83.6 ± 8.4 16 124.4 ± 16.1 13 120.2 ± 12.1 5th 7 65.5 ± 8.4 7 74.9 ± 11.6 5 69.6 ± 12.4 6th 1 258.0 0 - 2 65.5 ± 31.5 AP X ± S.E. AP 1st 9 49.7 ± 8.3 2nd 12 3rd aNumber of larv ae per i n s t a r per t e s t was 20. t ± 93 c l e a r l y a tren d f o r o v i p o s i t i o n in 2nd, 3rd and 4th i n s t a r s , as opposed to e a r l y or l a t e i n s t a r s . There i s , in g e n e r a l , c lo se agreement between these r e s u l t s and those recorded f o r host siz e preference (see Table 4 ) . I t i s very d i f f i c u l t to f i n d a s a t i s f a c t o r y expla nation f o r the h i g h e s t value in Table 30, a 6th i n s t a r l a r v a in the f i r s t t e s t with 258 cocoons. I t i s b e t t e r to t h in k o f t h i s value as an ex cep tion . Tables 31 through 36 contain a d d it i o n a l information on the production and d i s t r i b u t i o n of p a r a s i t i z e d in the cages. p a r a s i t o i d progeny among la r v a e The data were t a b u l a t e d according to the va rious combinations o f p a r a s i t o i d species and d e n s i t i e s t e s t e d . Rates o f emergence and female : male r a t i o s were c a l c u l a t e d where p o s s i b l e . Negative a t t a c k r a t e s and consequent f a i l u r e to produce any progeny are i n d ic a t e d by z ero s. E sp e c ia lly f o r A. m i l i t a r i s , i t i s e v id e n t t h a t an i n cre as e in host d e n s i ty r e s u l t e d in a g r e a t e r r a t e o f a t t a c k with a con cu rrent i n cre as e in t o t a l progeny production. Adult emergence e f f i c i e n c y varied from about 57% to 82%, and f o r the l a r g e s t sample (n = 99) was 76%. Throughout the whole experiment, r e g a r d l e s s o f ho st d e n s i ty used, progeny production always favored males. Where wasps were r e l e a s e d to search f o r th e h i g h e s t host d e n s i t i e s , female brood ranged from 42 to 68% o f the number of males. Comparing the n e t ou tput of Fj progeny a t th e h ig h e s t host d e n s i t y , A. m i l i t a r i s produced n e arly 13 times more o f f s p r i n g than did A. r u f i c r u s . The data j u s t described have been f u r t h e r subdivided to analyze the average number o f cocoons ( l a r v a e ) per p a r a s i t i z e d armyworm (Tables 34-36). The mean numbers of A. m i l i t a r i s cocoons per 94 T ab le 3 1. T o ta l Number o f Armyworms A ttacked When Caged w ith F ive A. m i l i t a r i s Females f o r 8 Hours and th e Number o f F. P a r a s ito id Progeny Produced Total Number, Rate or Ratio 1 Host Density' a 4 20 10 2 40 Total Number of Hosts P a r a s i t i z e d (n) 0 1 5 Cocoons Produced 0 43 P a r a s i t o i d s Emerged 0 Female Progeny Emerged Male Progeny Emerged 32 75 251 14 519 1250 2520 27 177 407 868 1861 0 9 89 96 264 554 0 18 88 311 604 1307 Rate o f Emergence (%) - 62.8 70.5 78.4 69.4 73.8 Sex Ratio o f Progeny ( ?/«r) - .5 1.0 .3 .4 .4 a 18 r e p lic a t e s f o r each h ost d e n s ity (6 re p s , each using 2nd, 3rd and 4 th in s t a r s ) . 95 Tab le 3 2. T o ta l Number o f Armyworms A ttacked When Caged w ith Ten A. m i l i t a r i s Females f o r 8 Hours and th e Number o f F. P a r a s ito id Progeny Produced Total Number, Rate or Ratio 1 Host Density3 4 20 10 2 40 Total Number of 1 9 7 35 62 99 Cocoons Produced 42 375 281 1686 2442 3511 P a r a s i t o i d s Emerged 24 294 229 1343 1903 2669 8 83 39 306 716 1081 16 211 190 1037 1187 1588 57.1 78.4 81.5 79.7 77.9 76.0 .5 .4 .2 .3 .6 .7 Hosts P a r a s i t i z e d (n) Female Progeny Emerged Male Progeny Emerged Rate o f Emergence (%) Sex Ratio o f Progeny (?/<*■) a 18 r e p lic a t e s f o r each h ost d e n s ity (6 re p s , each using 2nd, 3rd and 4 th in s t a r s ) . 96 T ab le 33. T o ta l Number o f Armyworms A ttacked When Caged w ith Ten A. r u f ic r u s Females f o r 8 Hours and the Number o f F. P a r a s ito id Progeny Produced 1 2 Host Density3 4 10 20 40 Hosts P a r a s i t i z e d (n) 0 0 0 0 2 12 Cocoons Produced 0 0 0 0 79 237 P a r a s i t o i d s Emerged 0 0 0 0 58 206 Female Progeny Emerged 0 0 0 0 23 98 Male Progeny Emerged 0 0 0 0 35 108 - - - - 73.4 86.9 - - - - .7 .9 Total Number, Rate or Ratio Total Number of Rate o f Emergence (%) Sex Ratio of Progeny {?/*) a 18 r e p lic a te s f o r each h o s t d e n s ity (6 re p s , each using 2nd, 3rd and 4 th in s t a r s ) . Table 34. T o ta l and Average Number o f Cocoons Produced from D if f e r e n t In s ta rs o f Armyworms P a ra s itiz e d (AP) When Caged With F ive A. m i l i t a r i s Females f o r 8 Hours 3rd I n s t a r 2nd I n s t a r Host Density APa TCPb TCP/APc APa TCPb 4th I n s t a r TCP/APc APa TCPb TCP/APc 1 0 0 0.0 0 0 0.0 0 0 0.0 2 0 0 0.0 0 0 0.0 1 43 43.0 4 0 0 0.0 4 167 41.8 ± 7.9 1 84 84.0 10 5 163 32.6 ± 6.5 7 219 31.3 ± 5.5 2 137 68.5 ± 21.5 20 7 279 39.9 ± 3.2 20 738 36.9 ± 2.0 5 233 46.6 ± 14.8 40 25 556 22.2 ± 2.1 29 836 28.8 ± 2.1 21 1128 aAP = no. of armyworms su c ce ss fu lly p a r a s i t i z e d . L TCP = t o t a l no. of cocoons produced by p a r a s i t o i d TCP/AP = avg. no. o f cocoons per p a r a s i t i z e d armyworm (mean ± S.E. of 6 r e p l i c a t e s ) 53.7 ± 5.4 Table 35. T o ta l and Average Number o f Cocoons Produced from D if f e r e n t In s ta rs o f Armyworms P a ra s itiz e d (AP) When Caged W ith Ten A. m i l i t a r i s Females f o r 8 Hours 3rd I n s t a r 2nd I n s t a r 4th I n s t a r Host Density APa TCPb TCP/APc APa TCPb 1 1 42 42.0 0 0 2 2 39 19.5 ± 2.5 3 145 4 4 97 24.3 ± 11.1 2 98 10 8 326 40.8 ± 5.0 13 804 61.8 ± 20 22 721 32.8 ± 2.4 31 1297 40 29 759 26.2 ± 3.1 46 1615 TCP/APc APa TCPb 0 0 4.1 4 191 47.8 ± 16.9 49.0 ± 20.0 1 86 86.0 9.1 14 556 39.7 ± 7.2 41.8 ± 5.3 9 424 47.1 ± 7.7 35.1 ± 3.2 24 1137 47.4 ± 3.8 0.0 48.3 ± aAP = no. of armyworms su c ce ss fu lly p a r a s i t i z e d bTCP = t o t a l no. of cocoons produced by p a r a s i t o i d cTCP/AP = avg. no. of cocoons per p a r a s i t i z e d armyworm (mean ± S.E. of 6 r e p l i c a t e s ) TCP/APc 0.0 Table 36. T o ta l and Average Number o f Cocoons Produced from D if f e r e n t In s ta rs o f Armyworms P a ra s itiz e d (AP) When Caged W ith Ten A. r u fic r u s Females f o r 8 Hours 3rd I n s t a r 2nd I n s t a r Host Density APa TCPb 1 0 0 2 0 4 TCP/APc APa TCPb 0.0 0 0 0 0.0 0 0 0 0.0 10 0 0 20 2 79 40 9 158 4th I n s t a r TCP/APc APa TCPb 0.0 0 0 0.0 0 0.0 0 0 0.0 0 0 0.0 0 0 0.0 0.0 0 0 0.0 0 0 0.0 39.5 ± 18.5 0 0 0.0 0 0 0.0 17.6 ± 3 79 26.3 ± 6.7 0 0 0.0 1.7 a AP = no. of armyworms su c c e ss f u lly p a r a s i t i z e d bTCP = t o t a l no. o f cocoons produced by p a r a s i t o i d /■» TCP/AP = avg. no. of cocoons per p a r a s i t i z e d armyworm (mean ± S.E. of 6 r e p l i c a t e s ) . TCP/APc 100 p a r a s i t i z e d armyworm l a r v a o f the same i n s t a r do no t appear to d i f f e r f o r e i t h e r level of p a r a s i t o i d d e n sity used. A sim ilar analysis is not p o s s ib l e f o r A. r u f i c r u s (Table 36) due to the small number of samples. When mean cocoon production was compared among d i f f e r e n t i n s t a r s , t h e r e was a tendency f o r smaller s iz e hosts to have fewer parasitoid larvae. This was observed when p a r a s i t o i d d e n s i ty was e i t h e r 5 or 10 wasps. Considering the reduced range of host s i z e s which were examined in t h i s experiment, more eggs were l a i d in 3rd and 4th i n s t a r larvae than in the younger 2nd i n s t a r s , which in p a r t supports the c o r r e l a t i o n e a r l i e r mentioned between host s i z e and number o f eggs l a i d . P a r a s i t o i d Development A summary of the l i f e cycle and developmental times as found in the l i t e r a t u r e was compiled, t o g e t h e r with rr\y own o b servation s on A. m i l i t a r i s in Table 37. ruficrus. Table 38 summarizes s i m i l a r data f o r A. I t should be noted t h a t thes e times are l a r g e l y dependent upon the r e a r i n g temperature regimes. Calkins and S u t t e r (1976) found, f o r i n s t a n c e , t h a t between 21 and 27°C A. m i l i t a r i s developmental time within £ . unipuncta c a t e r p i l l a r s decreased p r o p o r t i o n a l l y as the temperatures increas ed. Their rep o rted values were: ca. 31.5 days a t 21°C, 20 days a t 24°C, and 12.6 days a t 27°C. They noted t h a t the p a r a s i t o i d developed moderately well a t high tem p era tu re s, but armyworm m o r t a l i t y increas ed s u b s t a n t i a l l y with higher tem peratures. Table 39 shows the average days from p a r a s i t o i d o v ip o s i ti o n in the host to emergence; the data were t a b u l a t e d according t o host 101 Table 37. Duration of A. m i l i t a r i s Life Cycle from Egg to Adult from L i t e r a t u r e and Author's Observations3 Duration in Days According to Author Developmental Stage Tower (1915)° 3.3 2nd Stage 5.0 3rd Stagec 2.5 ' -> 12.6 15.0 J ->6.4 9,0 6 - 7dl Adultd Overal1 Life Cycle Rolim (1983) 23° 5.5 Egg 1st Stage Pupa0 Calkins & S u t t e r (1976) 27° 25 17 - 30 (x = 19 0) 4 - 8d2 18 - 26 (x = 22.1) aLab-reared on P_. unipuncta h o st. d o temperature r ec o r d ; experiments conducted in l a b o r a to r y but under c o n d itio n s as l i k e those o u tsid e as p o s s i b l e ; time spent in the cocoon was measured in an outdoor i n s e c t a r y . de v elop m e n t within cocoon. dProvided with food (d l = r a i s i n s ; d2 = 10% honey water m ix ture); 50% m o r t a l i t y . 102 Table 38. Duration of A. r u f i c r u s Life Cycle from Egg to Adult from L i t e r a t u r e and A uthor's Observations® Duration in Days According t o Author Developmental Stage Egg 1st Stage Hafez (1947) 26.5°C Rolim (1983) 23°C 5 .0 ^ 2nd Stage I 3.5 J 3rd Stage*3 O.s'A Pupa*3 5.2 J Adultc - 8 - 16 Overall Life Cycle - 17 - 21 (x = 19.6) 5.0 aLab-reared on A. i p s i l o n (Hafex 1947) or ------------------- >14.1 -------------------- > 5 . 5 P. unipuncta (Rolim 1983). ^Development w ithin cocoon. c Provided with 10% honey water m ixture; 50% m o r t a l i t y . 103 Table 39. Developmental Times from Oviposition to P a r a s i t o i d Larval Emergence from Various Armyworm I n s t a r s 9 A. m i l i t a r i s A. r u f i c r u s Instar Attacked Cocoon Massesb 1st 16 18.8 ± .6 20 15.1 ± .7 2nd 31 17.7 ± .5 35 14.7 ± .4 3rd 38 15.8 ± .4 32 13.1 ± .3 4th 42 12.3 ± .2 6 12.0 ± .3 5th 19 11.9 ± .2 - - 6th 3 12.0 ± .0 - - 149 - 93 - T o ta ls Overall Average (x) - Time in Days ( x ± S.E. ) 15.0 ± .3 a Reared a t 23.0 ± 1.5 °C bSame as no. o f p a r a s i t i z e d host l a r v a e . Cocoon. Masses - Time in Days ( x ± S.E. ) 14.1 ± .3 104 i n s t a r and p a r a s i t o i d s p e c i e s . I t i s ap paren t t h a t an inverse r e l a t i o n s h i p e x i s t s between h ost i n s t a r (o r s i z e ) and number of days spent in the host l a r v a , i . e . , i t takes lo nger f o r the p a r a s i t o i d larv a to develop in e a r l y than l a t e i n s t a r h o s t s , probably due to more food being a v a i l a b l e in l a r g e r l a r v a e . S im ila r ob se rv ation seems to apply to A. r u f i c r u s except t h a t data f o r 5th and 6th i n s t a r s are la c k in g , as ho st la r v a e were not p a r a s i t i z e d . Sh ortly before emerging from i t s h o st t h e Apanteles l a r v a molts i n t o a 3rd i n s t a r l a r v a . This i n s t a r u s u a l ly sp ins a cocoon on the back of i t s h o s t , and pupates in ca. 2 .5 days (A. m i l i t a r i s ) , o r l e s s than one day (A. r u f i c r u s ) (Tables 37 and 38). I t takes about 30 min f o r an emerging l a r v a t o lea ve i t s h o s t , and most o f them do i t a t the same time. When the l a r v a has emerged halfway i t s t a r t s spinning i t s s i l k e n cocoon. Cocoon-spinning i s completed in 1-2 hr. Calkins (1977) found the t o t a l time f o r cocoon c o n s t r u c t i o n t o be ca. 100 min, and Hafez (1947) e stim ate d t h a t A. r u f i c r u s spent about 120 min. E x te r n a l l y , the cocoons a re w h i t e r and c l o s e l y packed f o r A. mi 1i t a r i s , and y e ll o w i s h , l o o s e ly connected f o r A. r u f i c r u s . Adults o f both species from s i n g l e cocoon masses u s u a l ly emerge within 12 hr. or l e s s . Hafez (1947) observed t h a t among A. r u f i c r u s , male wasps u s u a l l y emerged f i r s t . The time spent by the 3rd i n s t a r and the pupa in the cocoon was a ls o recorded (Table 40). In c o n t r a s t to what was noted f o r duratio n o f th e egg and e a r l y l a r v a l p e r i o d , the average length o f the pupal s t a g e ( in clu d in g 3rd i n s t a r la r v a e and prepupae) was not influenced by the host i n s t a r in which the larv a e o r i g i n a t e d . This time averaged about 7 days f o r A. m i l i t a r i s and 5.5 days f o r A. r u f i c r u s . 105 Table 40. Developmental Times Between P a r a s i t o i d Larval Emergence from Various Armyworm I n s t a r s to Adult P a r a s i t o i d Emergence® A. mil i t a r i s A. r u f i c r u s Cocoon. Masses Instar Attacked Cocoon. Masses 1st 16 7.3 ± .1 20 5.6 ± .1 2nd 31 7.0 ± .1 35 5.5 ± .1 3rd 38 7.1 ± .1 32 5.7 ± .1 4th 42 7.4 ± .5 6 5.2 ± .3 5th 19 7.2 ± .1 - - 6th 3 6.7 ± .3 - - - 93 - 7.1 ± .1 - T o ta ls Overall Average (x) 149 - Time in Days ( x ± S.E. ) aReared a t 23.0 ± 1.5 °C. ^Same as no. of p a r a s i t i z e d host la r v a e . Time in Days ( x ± S.E. ) 5.5 ± .1 106 The mean developmental time from egg to a d u l t of each species was determined by adding the time from o v ip o s i ti o n u n t i l the 3rd i n s t a r emerged (Table 39), and the time spent i n sid e the cocoon (Table 40). The t o t a l developmental time found by Calkins and S u t t e r (1976) f o r A. mi 1i t a r i s ranged from 17 to 30 days and averaged 19 days a t 27°C (Table 37). In the p r e s e n t study, the t o t a l egg to a d u l t developmental period v a rie d from 18 to 26 days and depended on the h ost i n s t a r a tt a c k e d in a d d it i o n to tem perature; i t averaged 22.1 days a t 23°C. According to Hafez's (1947) o b servation s the egg to a d u l t developmental period f o r A. r u f i c r u s was about 19-20 days (Table 38). Although a d u l t A. r u f i c r u s l i v e d longer than A. m i l i t a r i s , the egg to a d u l t time of 19.6 days a t 23°C was somewhat shorter. Induced I n terna l Competition Intern a l competition i s a behavioral t r a i t of ten observed among p a r a s i t i c wasps developing c o n cu rren tly within the same h o st. occur as a r e s u l t of s u p e r p a r a sitis m or m u l t i p a r a s i t i s m . I t may In e i t h e r c a s e , some s o r t o f competition or c o n f l i c t or r e p r e s s i v e a ctio n occurs among the p a r a s i t o i d larv ae which a f f e c t s t h e i r development and s u r v i v a l . In some c a s e s , t h i s may r e s u l t in t o t a l suppression of one sp ecies by the o th er ( S a l t 1961; Fish er 1971). In t h i s experiment, 1 s t , 2nd and 3rd i n s t a r armyworm larva e were i n d i v i d u a l l y exposed to m u lt i p le p a r a s i t i s m in a small g l a s s chamber. (1 ml s t r a i g h t - s i d e d s h e l l v i a l ) . Females of each p a r a s i t o i d were allowed to o v i p o s i t once in the same host l a r v a , one species o r the o t h e r o v i p o s i ti n g f i r s t . Exposures were e i t h e r simultaneous (0-1 hr 107 group) or conducted over 24-, 48- or 96-hr i n t e r v a l s . General s u p e r i o r i t y was assumed f o r the species which managed to survive under supposedly competitive con ditions and which gave r i s e to unmixed progeny in more frequ en t case s. The r e s u l t s showing which sp ecies survived and emerged in each c ase , and t h e i r res p e c tiv e f r e q u e n c i e s , a re discussed below. A. r u f i c r u s seemed t o be a b e t t e r l a r v a l competitor in side the h o s t , having a n o tic ea b le advantage whenever i t o vip osite d f i r s t (Table 42). I f , however, A. m i l i t a r i s was the f i r s t to a t t a c k , A. r u f i c r u s o f f s p r i n g were predominant only when the exposure was almost simultaneous (Table 41). As exposure i n t e r v a l s were g r e a t e r than 24 h r , A. r u f i c r u s development was suppressed. Although competition may have played a s i g n i f i c a n t r o l e in deciding which species emerged f i r s t , t o t a l developmental time determines e a r l y or l a t e emergence. Thus, the apparent competitive a b i l i t y ex h ib ited by A. r u f i c r u s may hinge upon i t s s h o r t e r developmental time (see Tables 37 and 38). There i s , however, some doubt concerning the outcome of la r v a l competition between the two s p e c i e s , and one should be t o t a l l y aware t h a t t h i s di sc ussion i s s t i l l too s i m p l i s t i c to provide a s a t i s f a c t o r y explanation f o r the observed r e s u l t s . In asse ss in g t h e i r r e l a t i v e performances, these t e s t s should be considered l e s s re l e v a n t than the p a r a s i t o i d functional response study. I t may a ls o be of i n t e r e s t to observe t h a t the instances of mixed species were r a r e . The f a c t t h a t only one species gen erally emerged could have been determined by competitive e lim ina tio n or simply by r e s t r a i n t from o vip ositio n in hosts already containing a Table 4 1. Instar Exposed 1st 2nd P a r a s itiz a tio n o f E a rly In s ta r Armyworm Larvae Follow ing an A. m i l i t a r i s - A. r u fic r u s Exposure Sequence3 Hours Between Exposures x ± S.E. A. r u f . x ± S.E. Unaffected Host Larvae 0 - 3 12.7 ± 5.8 17 0 24 4 30.5 ± 3.8 4 27.3 ± 5.4 12 0 48 14 37.9 ± 3.1 1 96 8 32.0 ± 4.7 3 41.7 + 10.7 0 - 1 0 - 5 17.6 ± 39.3 ± 4.1 2 10.5 ± 3.5 26.1 ± 3.7 1 13.0 36.5 ± 7.7 0 - 48 96 9 (1) 14 8 (1) 0 - 1 0 - 24 2 48 96 a A. m i l . Other Unknown Deaths0 0 - 1 24 3rd P a r a s i to i d Species Emerged^ and Number of Cocoons Produced U (1) 4 105.0 3.5 5 [3] 0 9 [2] 0 15 0 9 [2] 0 5 0 11 1 9 29.6 ± 5.7 11 0 14.5 ± 2.5 8 (3) 21.8 ± 7.0 9 1 28.9 ± 4.4 4 31.3 ± 5.1 5 [1] 0 64.0 ± 9.2 0 16 [8] 0 - 20 host larvae used per t e s t . ^Values in parentheses i n d ic a t e frequency of mixed o f f s p r i n g ; the pre va lent species i s recorded f i r s t . c Values in brackets i n d ic a te frequency of host deaths between two successive exposures. Table 42. Instar Exposed 1st 2nd 3rd P a r a s itiz a tio n o f E a rly In s ta r Armyworm Larvae Follow ing an A. r u fic r u s - A. m i l i t a r i s Exposure Sequence3 P a r a s i to i d Species Emerged and Number of Cocoons Produced Other Unknown Deaths Unaffected Host Larvae Hours Between Exposures A. r u f . x ± S.E. A. m i l . 0 - 1 7 15.6 ± 2.5 0 - 13 0 24 12 17.3 ± 1.4 0 - 8 0 48 18 20.6 ± 1.1 0 - 2 0 96 16 20.8 ± .9 0 - 4 [4] 0 0 - 1 7 17.3 ± 3.7 1 56.0 11 1 24 3 27.7 ± 2.0 0 - 17 0 48 12 20.8 ± 1.1 0 - 8 0 96 10 26.2 ± 2.3 0 - 10 [4] 0 0 - 1 5 27.6 ± 7.7 0 - 15 0 24 3 19.3 + 7.7 2 63.5 ± 21.5 15 0 48 11 25.7 ± 1.5 0 - 8 [3] 1 96 8 22.1 ± 2.2 0 - 12 [11] 0 x ± S.E. a 20 host larvae used per t e s t . ^Values in br ackets in d ic a t e frequency of host deaths between two successive exposures. 110 d i f f e r e n t kind of p a r a s i t o i d egg. A r u f i c r u s r e p o r t e d ly cannot d i s t i n g u i s h p a r a s i t i z e d from n o n p a r a s i t iz e d Aqrotis hosts (Hafez 1947). Thus, the l a s t hypothes is cannot be suppo rted, a t l e a s t f o r t h i s sp e c i e s . Also, in a ccep tin g the f i r s t hypothesis one i s led to b e lie v e t h a t a l a r g e r number o f la r v a e might have escaped compe­ t i t i o n , thus making mixed progeny more f r e q u e n t ; however, t h a t was not what occurred. The second hypothesis ( d e t e r r e d o v i p o s i t i o n ) would seem, th u s , more a t t r a c t i v e although o v i p o s i ti o n by each female p a r a s i t o i d p a r t i c i p a t i n g in the t e s t s apparently did take place. A more c r u c i a l a s p e c t , however, i s t h a t the technique may be f a u l t y as an experimenter can never be t o t a l l y sure t h a t females have a c t u a l l y l a i d eggs to make t h i s a v a l i d t e s t . Although the experiment r a i s e s i n t e r e s t i n g q u e s t io n s on the biology and physiology of the sp e cie s involved, the method used i s adm ittedly u n s a t i s f a c t o r y to answer many of t h es e q u e s t i o n s . Additional anatomical and p h y sio lo g ic al s t u d i e s and d i s s e c t i o n s are deemed necessary i f com petitiv e i n t e r a c t i o n s and developmental processes taking place i n t e r n a l l y in the p a r a s i t i z e d host are to be expla in ed. Diss ectio ns o f l a r v a e a t various s t a g e s of t h e i r development are of utmost importance to d i s c l o s e some o f the i n t r i c a c i e s involved, and may help ex p la in why an " u n f i t " p a r a s i t o i d (see page 57), under c e r t a i n c o n d i t i o n s , may be r e p ro d u c t iv e ly s u p e r i o r t o an otherwise "more e f f e c t i v e and well-adapted" one. Tables 41 and 42 a l s o include unexplained host deaths (in clud in g those occurring between su ccess iv e exposures) and pupation as outcomes of the incubation phase. The number o f mature p a r a s i t o i d la r v a e c o n s t r u c t i n g cocoons provides an e stim ate of eggs l a i d by Ill individual females of both spe cie s in one quick i n s e r t i o n of the o v i p o s i t o r which o f ten l a s t s l e s s than 5 seconds. The number o f eggs per i n i t i a l i n s e r t i o n averaged 34 f o r A. m i l i t a r i s when t h i s p a r a s i t o i d a tt a c k e d f i r s t , and 21 f o r A. r u f i c r u s when i t a ttac k ed f i r s t (weighted means, n o t shown in t a b l e s ) . For the former s p e c i e s , Tower (1915) gave a range o f 8-72 eggs in one o v i p o s i t i o n ; f o r the l a t t e r , Hafez (1947) r ep o rte d an average of about 26 eggs f o r 9 Agr otis l a r v a e . Im plica tio ns f o r Biological Control and General Recommendations For many y e a r s g r e a t f i n a n c i a l l o s s e s to a g r i c u l t u r e have been caused by the armyworm. In Michigan, i n t e r e s t has increased since 1975 due to unusually fr e q u e n t y e a r l y outbreaks. Many independent f a c t o r s may have c o n tr i b u te d to the p res ent population s t a t u s o f t h i s p e s t . Some o f them have been i d e n t i f i e d , and should be given f u r t h e r a t t e n t i o n in f u t u r e s t u d i e s , as they may be major o b s t a c l e s in the design and implementation of armyworm management programs. (1) The following are worth noting: The d i f f i c u l t y o f d e t e c t i n g c e r t a i n l i f e sta g es ( i . e . , a d u l t s , eggs, 1 st and 2nd i n s t a r s ) in the f i e l d . This i s a frequent cause o f sudden crop damage (Riley 1883; S lin gerlan d 1897). Armyworm i n f e s t a t i o n s u s u a l ly go unnoticed u n t i l th e c a t e r p i l l a r s have reached l a t e r i n s t a r s and food consumption i s a t i t s g r e a t e s t p o i n t. The c h a r a c t e r i s t i c hiding behavior coupled with the p e s t ' s h a b i t of moving from one f i e l d to a n o th e r , make i t p a r t i c u l a r l y d i f f i c u l t to a s se ss regional d e n s i t i e s and to monitor the s p a t i a l and temporal 112 d i s t r i b u t i o n s of armyworm po pulations (Untung 1978), as e s s e n t i a l prereq u isite fo r e ffe c tiv e control. (2) £ . unipuncta i s a ls o known f o r i t s polyphagous feeding behavior; i t s larv a e have been r ep o r te d to feed on small g r a i n s , corn, sorghum, g r a s s e s , beans, forage c ro ps, vegetable crops and even a few f r u i t crops . With such a wide range o f h o s t s , a p p l i c a t i o n of adequate control measures i s not always easy. This problem may be f u r t h e r complicated by c l i m a t i c f l u c t u a t i o n s which may cause l a r v a l po pulations to move from grassy a re a s or low-value crops to a d ja c e n t, more economically important ones. (3) L i t t l e information on where armyworm po pulations o r i g i n a t e in outbreak and non-outbreak y e a r s i s a v a i l a b l e . A b e t t e r under­ standing of i t s general l i f e h i s t o r y ( e s p e c i a l l y e a r l y season development) i s c r i t i c a l f o r the s e l e c t i o n o f an e f f i c i e n t control strategy. (4) Being a m u l t i v o l t i n e s p e c i e s , armyworm population dynamics a r e complex, making some management s t r a t e g i e s l e s s a v a i l a b l e or economically u n f e a s i b l e . These are a s s o c i a t e d problems which g e n e r a l l y p o in t to a lack of information on the dynamics of armyworm po pulations and o f i t s ecosystem. This has r e s u l t e d in the p r a c t i c e of an "insurance"-type o f control where trea tm e n ts are o ften improperly a p p li e d , making i n s e c t i c i d e a p p l i c a t i o n s i n e f f e c t i v e and environmentally damaging. There have been su ggestions t h a t more f r eq u e n t l o c a l i z e d outbreaks might be due to the g r e a t e r use o f i n s e c t i c i d e s which k i l l o f f l a r g e numbers o f p a r a s i t o i d s and p red a to rs which normally may control the species ( e . g . , Breeland 1958). At p r e s e n t , however, the 113 c ause(s ) of l o c a l i z e d outbreaks a re unknown. In the f u t u r e , a more thorough study o f armyworm biology, p a r t i c u l a r l y with re f e r e n c e to i t s h a b it s and seasonal sy nchronization should be pursued. This will help determine the real c a u s e ( s ) o f outbreaks while providing f u t u r e workers with a d d it i o n a l da ta f o r in creased management o p tio n s . An are a which has rec eive d very l i t t l e a t t e n t i o n and where the lack of data is p a r t i c u l a r l y c r i t i c a l i s the study of r e l a t i o n s h i p s between the armyworm and i t s many na tu ra l enemies. Furthermore, the abundant and v aried complex o f p a r a s i t o i d species a t t a c k i n g armyworms provides a good o p po rtun ity to study the i n t e r a c t i o n o f p a r a s i t o i d g u ild s t h a t i s p a r t i c u l a r l y r e l e v a n t to the theory and p r a c t i c e of b i o lo g ic a l control o f i n s e c t s in temporary ecosystems (see Ehler and M i l le r 1978). One s p e c i e s which may be o f g r e a t i n t e r e s t due to i t s c lo s e a s s o c i a t i o n with the armyworm i s A. m i l i t a r i s . The high searching c h a r a c t e r i s t i c s o f t h i s i n s e c t (see page 5 7), a l l i e d with an app aren tly high n a tu r a l a b i l i t y to reproduce and catch up with small in c r e a s e s in the ho st p o pu lation , make i t a d e s i r a b l e organism f o r studying h o s t - p a r a s i t o i d i n t e r a c t i o n s both in the f i e l d and l a b o r a to r y . I t i s hoped t h a t t h i s study has c o n tr i b u te d to a b e t t e r understanding o f some f a c t o r s governing th es e h o s t - n a tu r a l enemy interactions. In g e n e r a l , s a t i s f a c t o r y chemical co ntrol measures are a v a i l a b l e to the farmer, but timing o f a p p l i c a t i o n i s f r e q u e n t ly a problem owing to the sporadic n a tu r e of armyworm outb reak s. Moreover, even though i n s e c t i c i d e usage may be regarded as a dependable, r a p id and e f f e c t i v e way to combat t h i s p e s t , the search f o r l e s s damaging environmental control o ptio ns should continue. I t appears t h a t 114 p e s t i c i d e usage can b e st be reduced by in c r e a s in g th e e f f i c i e n c y of n a tu ra l control a g en ts. Hence, i t i s rny opinion t h a t the b io lo g ic al control component should be i n t e g r a t e d with o t h e r c o ntrol measures. I t i s u n fortu n ate t h a t the i n t r o d u c t i o n o f A. r u f i c r u s did not r e s u l t in success ful e s ta b lis h m e n t. The door i s open, however, f o r a d d it i o n a l i n tr o d u c t i o n s o f new s t r a i n s of A. r u f i c r u s and/or d i f f e r e n t species in to Michigan, as well as o t h e r a re a s in the country. I b a s i c a l l y concur with van den Bosch's (1968) statement t h a t unsuccessful i n t r o d u c t i o n s should never be regarded as a f a i l u r e of the b i o lo g i c a l control method, but only as a f a i l u r e of e s t a b ­ lishment of c e r t a i n sp e cie s in some t a r g e t a r e a s . There i s probably c o n sid era ble p o t e n t i a l f o r applying b i o lo g i c a l c o ntrol to _P. u n ip u n cta , not to mention o t h e r major n octu id p e s t s ; however, the chances of success w i l l be g r e a t e r i f the approach o f m u ltip le i n t r o d u c t i o n s i s used. I t should be noted t h a t attempted e s t a b ­ lishment o f A. r u f i c r u s i n t o t h i s country did not have th e m u lt i p le c h a r a c t e r i s t i c s of many o t h e r b i o lo g i c a l c ontrol p r o j e c t s . Contrary t o a t y p i c a l l y " c l a s s i c a l " approach, whereby many d i f f e r e n t p a r a s i t o i d s are u s u a l ly introduced a t once, only one promising p a r a s i t o i d species was imported and a sse ss ed in t h i s p r o j e c t . Some empiricism may a ls o have been involved in t h i s p a r t i c u l a r study, but t h i s i s not a shortcoming per s e , sin ce the very p r a c t i c e of b io lo g i c a l p e st control has e s s e n t i a l l y had an empirical o r i g i n and f o r t u i t o u s e stablis hm ent o f e x o ti c n a tu ra l enemies i s not a l l t h a t uncomnon. Recently, techniques have been proposed t h a t can a s s i s t in s e l e c t i n g the b e st spe cie s f o r i n t r o d u c t i o n in to an are a with a known 115 species composition and d i s t r i b u t i o n (Price 1972; Ehler 1978). The use o f thes e methods may a ls o provide the b a sis f o r a s c i e n t i f i c assessment o f the r e s u l t s o f f u t u r e biolo gic al control p r o j e c t s . In a most i n t e r e s t i n g a n a l y s i s o f how a sequ ential r - K - s t r a t e g i s t s e r i e s o f p a r a s i t o i d s might evolve with a host i n s e c t , Force (1972) noted t h a t to control p e s t s in d i s t u r b e d environments ( a g r i c u l t u r a l , e t c . ) , the p r e f e r r e d n atu ral enemies should be r - s t r a t e g i s t s . These organisms are viewed as b e t t e r c o lo n iz e r s than K - s t r a t e g i s t s (see MacArthur and Wilson 1967, Pianka 1970, f o r d i sc u ssion s on the r - and K-selection concept). Some r e s e a r c h e r s ( e . g . , Ehler 1979) have f u r t h e r s t r e s s e d the need f o r d e t a i l e d s t u d i e s p r i o r to any i n t r o d u c ti o n . These s t u d i e s should indeed improve our understanding o f general competitive i n t e r a c t i o n s in endemic p a r a s i t o i d g u i l d s , thus allowing f o r more r a t i o n a l de cisio ns concerning new i n t r o ­ du ctions. As to the continued use of b io log ic al c o n t r o l , DeBach (1974) notes t h a t , as a r u l e , no geographic a r e a , crop or p e st i n s e c t should be prejudged as being u n s u i t a b l e f o r b io lo g ic al c o n t r o l . This has been a basic gu id elin e f o r many b io lo g ic al control workers. He a ls o shows impressive f i g u r e s on the number o f undescribed natural enemies. Among the p a r a s i t i c Hymenoptera alone , he estim ates t h a t only about 25% of a l l the sp ecies have been described (see a ls o Sabrosky 1955; Schlinger and Doutt 1964). This means t h a t "we have j u s t begun to s c r atc h the su rface in the search f o r i n s e c t natural enemies" (DeBach 1974), and t h a t a tremendous p o t e n t i a l e x i s t s for t h e i r increased use in a pp lied p e s t c o n t r o l . More s p e c i f i c a l l y , Mason (1981) mentions t h a t braconid p a r a s i t o i d s are poorly known, and the 1300 or so species of Apanteles 116 thus f a r d e sc r ib e d , r e p r e s e n t only a f r a c t i o n of t h e i r real number. Based on thes e e s t i m a t e s , one cannot help but hypothesize t h a t the p o t e n t i a l o f Apanteles sp ecies and t h e i r ecotypes in b i o lo g i c a l co ntrol o f noctuid p e s t s i s much g r e a t e r than p r e s e n t l y a t t a i n e d . An e v a lu a tio n o f the r e s u l t s provided by b i o lo g i c a l control res e a r c h a ls o shows t h a t in every area where t h i s method has been r i g o r o u s l y a p p l i e d , major successes have occurred (Munroe 1971). Rather than the c li m a t e , crop or p e s t , major success has often been d i r e c t l y r e l a t e d to the res ea rch and funds t h a t are u t i l i z e d (DeBach 1964; Simmonds e t a l . 1976). I n t e n s i v e , w e ll- s u p p o rte d programs a r e , o f c o u rs e, l i k e l y to be more successful than i s o l a t e d small p r o j e c t s . Accordingly, i f b i o lo g i c a l c ontrol o f a lep id o p tero u s p e s t be the u l tim a te o b j e c t i v e o f f u t u r e p r o j e c t s , a sequence of i n t r o ­ ductions of p a r a s i t o i d s of known v a lu e , such as o u t l i n e d by Force (1972) would be advised. That, of cou rse, would imply increas ed f i n a n c i a l support sin c e more i n te n s i v e l a b o r a to r y and f i e l d e v a l u a t i o n of a l l species concerned w ill be r e q u i r e d . LITERATURE CITED LITERATURE CITED Abies, J . R. and M. Shepard. 1976. Seasonal abundance and a c t i v i t y of indigenous hymenopterous p a r a s i t o i d s a t t a c k i n g the house f l y (Diptera: Muscidae). Can. Ent. 108: 841-844. Anon. 1975. Report f o r the y e a r ended 31 March 1975. Report o f the Dept, o f S c i e n t i f i c and I n d u s t r i a l Research, New Zealand (1975), 76 pp. Baker, A. W. 1915. The army worm in Ontario in 1914. Ann. Rept. Ent. Soc. Ontario 45: 75-90. Baker, A. W. 1939. Notes on th e armyworm, Leucania unipuncta Haw. outbreak in Ontario in 1938. Ann. Rept. Ent. Soc. Ontario 69: 96-99. B a r t l e t t , B. R. and R. van dan Bosch. 1964. Foreign e x p lo r a tio n f o r b e n e f i c i a l organisms. In: Biological Control of I n s e c t Pest s and Weeds, ed. P. DeBach, pp. 283-304. Reinhold Pub!. Corp., New York, NY. 844 pp. Breeland, S. G. 1958. B iological s t u d i e s on the armyworm Pseu da letia unipuncta (Haworth), in Tennessee (Lepidoptera: Noctuidae). J . Tenn. Acad. Sc i. 33: 263-347. B r i t t o n , W. E. 1915. Outbreak of the armyworm Heliophila unipuncta. Conn. Agric. Expt. Sta . Rept. f o r 1914; 157-173. B urn ett, T. 1951. E f f e c t s o f temperature and ho st d e n sity on the r a t e o f i n cre as e of an i n s e c t p a r a s i t e . Amer. Nat. 85: 337-352. Burn ett, T. 1953. E f f e c t s o f temperature and p a r a s i t e d e n sity on the r a t e of i n cre as e of an i n s e c t p a r a s i t e . Ecology 34: 322-328. Burn ett, T. 1954. In fluences o f n a tu ra l temperatures and c o n t r o l l e d host d e n s i t i e s on o v i p o s i t i o n of an i n s e c t p a r a s i t e . Physiol. Zool. 27: 239-248. B urn e tt, T. 1956. E f fe c t s of n a tu ra l temperatures on o v i p o s i ti o n of various numbers of an i n s e c t p a r a s i t e (Hymenoptera, Cha lcididae, T enth red inid ae ). Ann. Ent. Soc. Amer. 49: 55-59. Burn ett, T. 1958. Dispersal of an i n s e c t p a r a s i t e over a small p l o t . Can. Ent. 90: 279-283. 117 118 Calkins, C. 0. 1977. Notes on the cocoon c o n s t r u c t io n behavior of Apanteles m i l i t a r i s (Note). Fla. Ent. 60: 65. Calkins, C. 0. and G. R. S u t t e r . 1976. Apanteles m i l i t a r i s and i t s host Ps eu d a letia unipuncta: Biology and r e a r i n q . Env. Ent. 5: 147-150. Chambers, D. L. 1977. Q uality co ntrol in mass r e a r i n g . Ann. Rev. Ent. 22: 289-308. Clausen, C. P. 1962. Entomophagous I n s e c t s . McGraw-Hill Book Co., New York, NY. (Reprint E d it i o n , Hafner Publ. Co., New York, NY.) 688 pp. Clausen, C. P. e t a l . 1977. Introduced p a r a s i t e s and p r e d a to r s of arthropod p e s t s and weeds: A world review. U.S. Dept. Agr., Agr. Handbook No. 480, 551 pp. Corbet, P. S. and R. F. Smith. 1976. I n t e g r a te d c o n t r o l : A r e a l i s t i c a l t e r n a t i v e to misuse of p e s t i c i d e s ? In: Theory and P r a c t i c e of Biological Control, ed. C. B. Huffaker and P. S. Messenger, pp. 661-682. Academic P r e s s , New York, NY. 788 pp. C rid dle , N. 1914. The value of some mammals and b i r d s as d e s t r o y e r s o f noxious i n s e c t s . Ottawa Nat. 28: 119-124. Cumber, R. A., D. J . Allan and L. Helmore. 1977. In tr o d u c tio n and successful estab lis h m en t in New Zealand of f u r t h e r s t r a i n s o f Apanteles r u f i c r u s (Hymenoptera: Braconidae) to combat P s eu d a letia (Mythimna) s e p a r a ta (Walk.) (Lepidoptera: Noctuidae). N. Z. J . Agr. Res. 20: 255-258. Davis, J . J . and A. F. S a t t e r t h w a i t . 1916. Life h i s t o r y s t u d i e s of Cirphis unipuncta (Haworth), t h e t r u e armyworm. J . Agr. Res. 6: 799-812. DeBach, P. 1964. Successes, t r e n d s , and f u t u r e p o s s i b i l i t i e s . In: Biological Control o f I n s e c t Pests and Weeds, Ed. P. DeBach, pp. 673-713. Reinhold Publ. Co., New York, NY. 844 pp. DeBach, P. 1971a. The use o f imported n a tu ra l enemies in i n s e c t p e st management ecology. Proc. Tall Timbers Conf. Ecol. Anim. Contr. Habit. Mgmt. 3: 211-233. DeBach, P. 1971b. P r i n c i p i o s y p o s s i b i l i d a d e s del control biolo gico de l a s plaga s. Bol etin Soc. Ent. Peru 6: 39-47. DeBach, P. 1974. Biological Control by Natural Enemies. Cambridge U niv e rsity P re ss , New York, NY. 323 pp. DeBach, P. and B. R. B a r t l e t t . 1964. Methods of c o l o n i z a t i o n , recovery and e v a l u a t i o n . In: Biological Control of I n s e c t Pests and Weeds, ed. P. DeBach, pp. 402-426. Reinhold Publ. Co., New York, NY. 844 pp. 119 DeBach, P. and C. B. Huffaker. 1971. Experimental tec hn iques f o r e v a lu a tio n o f the e f f e c t i v e n e s s o f na tu ra l enemies. In: Biological C on tro l, ed. C. B. Huffaker, pp. 113-140. Plenum P r e s s , New York, NY. 5 i l pp. DeBach, P . , C. B. Huffaker and A. W. MacPhee. 1976. Evaluation of the impact of n a tu r a l enemies. In: Theory and P r a c t i c e of Biological C ontrol, ed. C. B. Huffaker and P. S. Messenger, pp. 255-285. Academic P r e s s , New York, NY. 788 pp. DeBach, P. and H. S. Smith. 1941. The e f f e c t o f ho st d e n s i ty on the r a t e o f rep rod u c tio n of entomophagous p a r a s i t e s . J . Econ. Ent. 34: 741-745. DeBach, P . , and H. S. Smith. 1947. E f f e c t s of p a r a s i t e population d e n s i ty on r a t e o f change o f host and p a r a s i t e p o pu lation s. Ecology 28: 290-298. Doutt, R. L. 1964. Biolo gical c h a r a c t e r i s t i c s o f entomophagous a d u l t s . In: B iological Control o f I n s e c t Pest s and Weeds, ed. P. DeBach, pp. 145-167. Reinhold Publ. Co., New York, NY. 844 pp. Doutt, R. L . , D. P. Annecke and E. Tremblay. 1976. Biology and host r e l a t i o n s h i p s of p a r a s i t o i d s . In: Theory and P r a c t i c e of Biolo­ gical C ontrol, ed. C. B. Huffaker and P. S. Messenger, pp. 143-168. Academic P r e s s , New York, NY. 788 pp. Doutt, R. L. and P. DeBach. 1964. Some b i o lo g i c a l c o ntrol concepts and q u e s t io n s . In: Biolo gical Control o f I n s e c t P e sts and Weeds, ed. P. DeBach, pp. 118-142. Reinhold Publ. Co., New York, NY. 844 pp. E hle r, L. E. 1977. P a r a s i t i z a t i o n o f cabbage looper in C a l i f o r n i a c o t t o n . Env. Ent. 6: 783-784. E hle r, L. E. 1978. Competition between two n a tu ra l enemies o f Medi­ t e r r a n e a n black s c a l e . Env. Ent. 7: 521-523. Ehler, L. E. 1979. Assessing com petitiv e i n t e r a c t i o n s in p a r a s i t i c g u i ld s p r i o r to i n t r o d u c t i o n . Env. Ent. 8: 558-560. E hle r, L. E. and J . C. M i l l e r . 1978. B iological control in temporary agroecosystems. Entomophaga 23: 207-212. Fernald, H. T. 1914. The armyworm. Mass. S t a te Board Agric. Circ. 22: 1-13. F i s h e r , R. C. 1971. Aspects o f th e physiology o f e n d o p a r a s i t i c Hymenoptera. Biol. Rev. Cambridge P h ilo s. Soc. 46: 243-278. Force, D. C. 1972. r - and K - s t r a t e g i s t s in endemic h o s t - p a r a s i t o i d communities. Bull. Ent. Soc. Amer. 18: 135-137. 120 Force, D. C. 1974. Ecology of i n s e c t h o s t - p a r a s i t o i d communities. Science 184: 624-632. Force, D. C. 1975. Succession of r - and K - s t r a t e g i s t s in p a r a s i t o i d s . In: Evolutionary S t r a t e g i e s o f P a r a s i t i c I n s e c t s and Mites, ed. P. W. P r i c e , pp. 112-129. Plenum P r e s s , New York, NY. 224 pp. Gibson, A. 1915a. The army worm, Cirphis unipuncta Haw. Can. Dept. Agr. Ent. Bull. 9: 1-34. Gibson, A. 1915b. The 1914 outbreak of the army worm in Canada. Ann. Rept. Ent. Soc. Ontario 45: 72-75. G i l l , J . L. 1978a. Design and Analysis of Experiments in the Animal and Medical Sciences. (Vol. I) The Iowa S t a te U n iv e rs ity Pre ss, Ames, IA. 409 pp. G i l l , J . L. 1978b. Design and Analysis of Experiments in the Animal and Medical s c i e n c e s . Volume 3: Appendices. The Iowa S t a te U n iv e rs ity P r e s s , Ames, IA. 173 pp. Godfrey, G. L. 1972. A Review and R e c l a s s i f i c a t i o n of Larvae o f the Subfamily Hadeninae (Lepidoptera: Noctuidae) o f America North o f Mexico. U. S. Dept. Agr. Tech. Bull. 1450, 265 pp. G r i f f i t h s , K. J . 1969. The importance of coincidence in the f u n c tio n a l and numerical responses o f two p a r a s i t e s of the European pine sawfly, Neodiprion s e r t i f e r . Can. Ent. 101: 673-713. Guppy, J . C. 1961. L if e h i s t o r y and behaviour of the armyworm, P s e u d a l e t ia unipuncta (Haw.) (Lepidoptera: Noctuidae), in e a s t e r n Ontario. Can. Ent. 93: 1141-1153. Guppy, J . C. 1967. I n s e c t p a r a s i t e s o f the armyworm, P s eu d a letia unipuncta (Lepidoptera: Noctuidae), with notes on sp ecies observed in Ontario. Can. Ent. 99: 94-106. Hafez, M. 1947. The biology and l i f e - h i s t o r y of Apanteles r u f i c r u s Hal. (Hymenoptera-Braconidae). Bull. Soc. Fouad l e r Entom. 31: 225-249. Hagen, K. S . , S. Bombosch and J . A. McMurtry. 1976. The biology and impact o f p r e d a t o r s . In: Theory and P r a c t i c e o f Biological C on tro l, ed. C. B. Huffaker and P. S. Messenger, pp. 93-142. Academic P r e s s , New York, NY. 788 pp. H a s s e l l , M. P. 1966. Evaluation of p a r a s i t e or p r e d a t o r responses. J . Anim. Ecol. 35: 65-75. H a s s e l l , M. P. 1978. The Dynamics o f Arthropod Predator-Prey Systems. Princeton U n iv e rs ity P r e s s , Prin c eto n , NJ. 237 pp. 121 H i l l , R. L. 1977. P a r a s i t e helps control army c a t e r p i l l a r . N. Z. J. of Agr. 134: 21-22. H ollin g, C. S. 1959a. The components of pred a tio n as revealed by a study o f small mammal pr edatio n of the European pine sawfly. Can. Ent. 91: 293-320. Holling, C. S. 1959b. Some c h a r a c t e r i s t i c s of simple types o f pred atio n and p a r a s i t i s m . Can. Ent. 91: 385-398. Hollin g, C. S. 1961. P r i n c i p l e s o f i n s e c t pred a tio n . Ann. Rev. Ent. 6: 163-182. H o llin g, C. S. 1965. The f u nctio n al response o f p r e d a t o r s to prey d e n sity and i t s r o l e in mimicry and po pulation r e g u l a t i o n . Mem. Ent. Soc. Can. 45: 3-60. Hol ling, C. S. 1966. The f un ctio n al response o f i n v e r t e b r a t e p red a to rs to prey d e n s i t y . Mem. Ent. Soc. Can. 48: 1-86. Huffaker, C. B. 1974. Some e cologic al r o o t s of p e s t c o n t r o l . Entomophaga 19: 371-389. Huffaker, C. B., C. E. Kennett, B. Matsumoto and E. 6. White. 1968. Some parameters in the r o l e of enemies in the na tu ra l control of i n s e c t abundance. In: In se ct Abundance, ed. T. R. E. Southwood, pp. 59-75. Blackwell S c i e n t i f i c P u b l i c a t i o n s , Oxford. 160 pp. Huffaker, C. B., F. J . Simmonds and J . E. Laing. 1976. The t h e o r e t i c a l and empirical b a s i s of b i o lo g i c a l c o n t r o l . In: Theory and P r a c t i c e o f Biological C o ntrol, ed. C. B. Huffaker and P. S. Messenger, pp. 41-78. Academic P r e s s , New York, NY. 788 pp. Huffaker, C. B. and P. S. Messenger. 1964. The concept and s i g n i ­ f i c a n c e o f na tu ra l c o n t r o l . In: Biological Control o f I n se c t Pe sts and Weeds, ed. P. DeBach, pp. 74-117. Reinhold Publ. Co., New York, NY. 844 pp. Huffaker, C. B., P. S. Messenger and P. DeBach. 1971. The natural enemy component in n a tu ra l control and the theory o f biolo gic al c o n t r o l . In: Biological C o n tro l, ed. C. B. Huffaker, pp. 16-67. Plenum P r e s s , New York, NY. 511 pp. King, V. and G. W. Barber. 1921. C o n tro lling the armyworm in south­ e a s t Missouri. J . Econ. Ent. 14: 486-488. Knight, H. H. 1916. The armyworm in New York in 1914. Cornell Univ. Agr. Expt. Sta. Bull. 376: 751-765. Laing, J . 1937. H os t-fi nding by i n s e c t p a r a s i t e s . I . Observations on the f in d in g o f hosts by Alysia manducator, Mormoniel!a v i t r i p e n n i s and Trichoqramma evanescens. J . Anim. Ecol. 6: 298-317. 122 MacArthur, R. H. and E. 0. Wilson. 1967. The Theory of Island Bio­ geography. Princeton University P re ss , Prin c eto n , NJ. 203 pp. Mason, W. R. M. 1981. The p o ly p hy le tic nature o f Apanteles F o e r ste r (Hymenoptera: Braconidae): A phylogeny and r e c l a s s i f i c a t i o n of M icrogastrinae. Mem. Ent. Soc. Can. 115: 1-147. Mayr, E. 1965. Summary. In: The Genetics of Colonizing Species, ed. H. G. Baker and G. L. Stebb in s, Academic Press I n c . , New York, NY. 588 pp. Messenger, P. S. 1968. Bio climatic s t u d i e s of the aphid p a r a s i t e Praon exsoletum. I. E f fe c ts of temperature on the f u n ctio nal response o f females to varying host d e n s i t i e s . Can. Ent. 100: 728-741. Messenger, P. S . , F. Wilson and M. J . Whitten. 1976. V a r ia t io n , f i t n e s s and a d a p t a b i l i t y of na tu ra l enemies. In: Theory and P r a c t i c e o f Biological C ontrol, ed. C. B. Huffaker and P. S. Messenger, pp. 209-231. Academic Press, New York, NY. 788 pp. Michelbacher, A. E. 1945. The importance o f ecology in i n s e c t c o n t r o l . J . Econ. Ent. 38: 129-130. Mickel, C. E. 1932. Armyworms in southern Minnesota. J . Econ. Ent. 25: 1123-1128. M i l l e r , J . C. 1977. Ecological r e l a t i o n s h i p s among p a r a s i t e s of Spodoptera p r a e f i c a . Env. Ent. 6: 581-585. M i l l e r , J . C. 1980. Niche r e l a t i o n s h i p s among p a r a s i t i c i n s e c t s occurring in a temporary h a b i t a t . Ecology 61: 270-275. Mohyuddin, A. I. and S. Shah. 1977. Biological control o f Mythimna s e p ara ta (Lepidoptera: Noctuidae) in New Zealand and i t s bearing on b i o lo g ic a l control s t r a t e g y . Entomophaga 22: 331-333. Muesebeck, C. F. W. 1921. A r e v i s io n of the North American spe cie s of Ichneumon-flies belonging to the genus A pa n teles. U.S. Nat. Mus. Proc. 58: 483-576. Muesebeck, C. F. W., K. V. Krombien and H. K. Townes. 1951. Hymenop­ t e r a of America North of Mexico. Synoptic Catalog. U.S. Dept. Agr., Agr. Monogr. 2, 1420 pp. Munroe, E. G. 1971. S t a tu s and p o t e n t i a l of b io lo g ic al control in Canada. Commonw. I n s t . Biol. Control Tech. Commun. 4: 213-255. Murdoch, W. W. 1969. Switching in general p r e d a t o r s : Experiments on p red a to r s p e c i f i c i t y and s t a b i l i t y of prey p o p ulation s. Ecol. Mon. 39: 335-354. 123 Murdoch, W. W., and A. Oaten. 1975. Predation and population s t a b i l i t y . Adv. Ecol. Res. 9: 2-131. Nicholson, A. J . 1933. The balance of animal populations. J . Anim. Ecol. 2 ( S u p p l.) : 132-178. Panton, J . H. 1897. Two i n s e c t p e s t s in 1896. Ann. Rept. Ent. Soc. Ontario 27: 44-54. Pianka, E. 1970. On r - and K - s e le c tio n . Amer. Nat. 104: 592-597. Pianka, E. 1972. r - and K -selec tio n or b- and d - s e l e c t i o n . Amer. Nat. 106: 581-588. Pond, D. D. 1960. Life h i s t o r y s t u d i e s of the armyworm, P s eu d a letia unipuncta (Lepidoptera: Noctuidae), in New Brunswick. Ann. Ent. Soc. Amer. 63: 661-665. ( E r r a t a 1961, Ann. Ent. Soc. Amer. 54: 168). P r i c e , P. W. 1972. Methods of sampling and a n a l y s i s f o r p r e d i c t i v e r e s u l t s in the i n tr o d u c ti o n of entomophagous i n s e c t s . Entomophaga 17: 211-222. P r i c e , P. W. 1973. P a r a s i t o i d s t r a t e g i e s and community o r g a n i z a t i o n . Env. Ent. 2: 623-626. Pschorn-Walcher, H. 1977. Biological control o f f o r e s t i n s e c t s . Ann. Rev. Ent. 22: 1-22. Rile y, C. V. 1883. The arir\y worm (Leucania unipuncta Haw.). Chapter VI in Third Report o f the U.S. Entomological Commission, U.S.D.A. pp. 89-156. Government P r i n t in g O f f ic e , Wash. D.C. Rings, R. W. and G. J . Musick. 1976. A p i c t o r i a l f i e l d key to the armyworms and cutworms a t t a c k i n g corn in the North Central s t a t e s . Ohio Agr. Res. and Dept. C t r . , Res. Circ. 221: 1-36. Ruppel, R. F. 1979a. P r o t e c t in g f i e l d crops from arnryworms. Michigan S t a te U nivers ity Extension Bull. E-755. 3 pp. Ruppel, R. F. 1979b. S t a tu s of general feeding i n s e c t s in Michigan's f i e l d crops in 1979. Michigan S t a t e University Cooperative Extension Service I n s e c t Newsle tter, No. 79-18. 7 pp. Ruppel, R. F. and G. W. Bird. 1981. 1981 p e s t i c i d e recommendations f o r i n s e c t and nematodes of f i e l d and forage crop s. Michigan S t a te U n ivers ity Cooperative Extension Service. 13 pp. Sabrosky, C. W. 1955. The i n t e r r e l a t i o n s of bio lo g ic al control and taxonomy. J . Econ. Ent. 48: 710-714. S a l t , G. 1961. Competition among i n s e c t p a r a s i t o i d s . Biol. 15: 96-119. Symp.Soc. Exp. 124 S c h a ff n e r, J . V. and C. L. Griswold. 1934. Macro!epidoptera and t h e i r p a r a s i t e s r e a red from f i e l d c o l l e c t i o n s in the n o r t h - e a s t e r n p a r t o f the United S t a t e s . U.S. Dept. Agr. Misc. Publ. 188, 160 pp. S c h l in g e r , E. I . and R. L. Doutt. 1964. Systematics in r e l a t i o n to b io lo g ic al c o n t r o l . In: B iological Control of I n s e c t P ests and Weeds, ed. P. DeBach, pp. 247-280. Reinhold Publ. Co., New York, NY. 844 pp. Simmonds, F. J . 1963. Genetics and b io lo g ic al c o n t r o l . Can. Ent. 95: 561-567. Simmonds, F. J . 1972. Approaches t o b i o lo g i c a l c ontrol problems. Entomophaga 17: 251-264. Simmonds, F. J . , J . M. Franz and R. I . S a i l e r . 1976. History of bio ­ lo g ic a l c o n t r o l . In: Theory and P r a c t i c e o f Biolo gical Control, ed. C. B. Huffaker and P. S. Messenger, pp. 17-39. Academic P r e s s , New York, NY. 788 pp. S l i n g e r l a n d , M. V. 1897. The army worm in New York. Cornell Univ. Agr. Expt. Sta . B u ll. 133: 233-258. Smith, H. S. 1929. Multip le p a r a s i t i s m : I t s r e l a t i o n t o th e b io lo g ic al c ontrol of i n s e c t p e s t s . Bull. Ent. Res. 20: 141-149. Smith, H. S. 1939. I n s e c t p o pulations in r e l a t i o n to b io lo g i c a l c o n t r o l . Ecol. Monogr. 9: 311-320. Smith, H. S. 1941. Racial se g rega tio n in i n s e c t p op ulatio n s and i t s s i g n i f i c a n c e in a p p lie d entomology. J . Econ. Ent. 34: 1-13. Solomon, M. E. 1949. The n a tu ra l control o f animal p o p u l a t i o n s . J . Anim. Ecol. 18: 1-35. S t a r k , R. W. and R. F. Smith. 1971. Systems a n a l y s i s and p e s t manage­ ment. In: Biological C ontrol, ed. C. B. Huffaker, pp. 331-345. Plenum P r e s s , New York, NY. 511 pp. S t e e l , R. G. D. and J . H. T o r ri e . 1980. (2nd e d . ) P r i n c i p l e s and Procedures of S t a t i s t i c s : A Biometrical Approach. McGraw-Hill Book Co., New York, NY. 633 pp. Thompson, W. R. 1939. Biological c ontrol and the t h e o r i e s of the i n t e r a c t i o n s o f p o p u la tio n s. P a r a s ito lo g y 31: 299-388. Thompson, W. R. 1945. A Catalogue o f the P a r a s i t e s and Predators of I n s e c t P e s t s . Section 1, Pa rt 6, pp. 134-136. The Imperial P a r a s i t e S e rvice , B e l l e v i l l e , O ntario, Canada. Tower, D. G. 1915. Biology of Apanteles m i l i t a r i s . J . Agr. Res. 5: 495-507. 125 Treherne, R. C. 1916. A pr eliminary l i s t of p a r a s i t i c i n s e c t s known to occur in Canada. Ann. Rept. Ent. Soc. Ontario 46: 178-193. T u rnb u ll, A. L. 1967. Population dynamics o f e x o tic i n s e c t s . Bull. Ent. Soc. Amer. 31: 333-337. T u rnb u ll, A. L . , and D. A. Chant. 1961. The p r a c t i c e and theory of b i o lo g i c a l control o f i n s e c t s in Canada. Can. J . Zool. 39: 697-753. U l l y e t t , G. C. 1943. Some a s p e c t s of p a r a s i t i s m in f i e l d populations o f P l u t e l l a maculipennis Curt. J . Ent. Soc. Sthn. A frica 6: 65-80. U l l y e t t , G. C. 1945. D i s t r i b u t i o n of progeny by Microbracon hebetor Say. J . Ent. Soc. Sthn. Africa 8: 123-131. U l l y e t t , G. C. 1949a. D i s t r i b u t i o n o f progeny by Che!onus texanus Cress. (Hymenoptera: Braconidae). Can. Ent. 81: 25-44. U l l y e t t , G. C. 1949b. D i s t r i b u t i o n of progeny by Cryptus in o rnatu s P r a t t (Hymenoptera: Ichneumonidae). Can. Ent. 81: 285-299. U l l y e t t , G. C. 1950. D i s t r i b u t i o n of progeny by Cryptus in orn atus P r a t t (Hymenoptera: Ichneumonidae). Can. Ent. 82: 1-11. Untung, K. 1978. The d i s t r i b u t i o n and bionomics o f the arrnyworm, P s e u d a le tia unipuncta (Haw.) in Michigan. Ph.D. D i s s e r t a t i o n , Dept, o f Entomology, Michigan S t a te U n i v e r s i ty , East Lansing, 247 pp. van den Bosch, R. 1968. Comments on population dynamics of e x o ti c i n s e c t s . B ull. Ent. Soc. Amer. 14: 112-115. van den Bosch, R. 1971. Biolo gical control of i n s e c t s . Ann. Rev. Ecol. Syst. 2: 45-66. Vickery, R. A. 1925. L i s t of p a r a s i t i c i n s e c t s reared from host i n s e c t s c o l l e c t e d in the v i c i n i t y of Brownsville, Texas. Proc. Ent. Soc. Wash. 27: 137-141. Vinson, S. B. and G. F. Iwantsch. 1980. Host s u i t a b i l i t y f o r i n s e c t p a r a s i t o i d s . Ann. Rev. Ent. 25: 397-419. Walker, M. G. 1937. Notes on the d i s t r i b u t i o n o f Cephus pygmaeus, L in n . , and o f i t s p a r a s i t e , C o l ly r i a c a l c i t r a t o r Grav. B u ll. Ent. Res. 30: 551-573. Walton, W. R. 1916. The t r u e arnyworm and i t s c o n t r o l . U.S. Dept. Agr. Farmers B u ll. 731, 12 pp. Watt, K. E. F. 1965. Community s t a b i l i t y and the s t r a t e g y o f bio­ l o g i c a l c o n t r o l . Can. Ent. 97: 887-895. 126 Wi 11 co ck s, F. C. 1937. The I n s e c t s and Related P e sts of Egypt. Vol. I , P a r t 2, pp. 447, 708 and 768. The Royal A g r ic u ltu r a l So ciety, Cairo, Egypt. Woodworth, C. W. 1896. Remedies f o r i n s e c t s and fu n g i. C a l i f . Agr. Expt. Sta. Bull. 115: 1-16. Woodworth, C. W. 1908. The theory o f the p a r a s i t i c control o f i n s e c t p e s t s . Science 28: 227-230. Zwolfer, H., M. A. Ghani and V. P. Rao. 1976. Foreign e x p lo r a tio n and importation of n a tu ra l enemies. In: Theory and P r a c t i c e of Biological C ontrol, ed. C. B. Huffaker and P. S. Messenger, pp. 189-207. Academic Press, New York, NY. 788 pp. APPENDIX 1 APPENDIX 1 Record o f D e p o sitio n o f Voucher Specim ens* The specim ens l i s t e d on the fo llo w in g s h e e t ( s ) have been d e p o site d in th e named museum(s) as sam ples o f th o se s p e c ie s or o th e r taxa which were used in t h i s r e s e a r c h . Voucher r e c o g n it io n la b e ls b e a r in g th e Voucher No. have been a tta c h e d or in clu d ed in flu id -p r e s e r v e d sp ecim en s. Voucher N o.:____ 1983-2_______________________ T it le o f t h e s is o r d is s e r t a t io n (o r o th e r r ese a rc h p r o j e c t s ) : Laboratory Comparison of the P o t e n ti a l of Apanteles r u f i c r u s Haliday and Apanteles m i l i t a r i s Walsh (Hymenoptera: Braconidae) f o r Control o f the Armyworm, Ps eu da letia unipuncta (Haworth) (Lepidoptera: Noctuidae) in Michigan Museum(s) where d e p o site d and a b b r e v ia tio n s fo r ta b le on fo llo w in g s h e e t s : Entomology Museum, M ichigan S ta te U n iv e r s ity (MSU) Other Museums: None I n v e s t i g a t o r 's Name ( s ) (ty p ed ) Antonio Edilton Rolim_________ Date June 1983_____ *R eference: Y oshim oto, C. M. 1978. Voucher Specimens fo r Entomology in North A m erica. B u ll. Entomol. S oc. Amer. 2 4 :1 4 1 -4 2 . D ep o sit as fo llo w s : O r ig in a l: C op ies: In clu d e as Appendix 1 in ribbon copy o f t h e s is or d is s e r t a t io n . In clu d ed as Appendix 1 in c o p ie s o f t h e s i s or d is s e r t a t i o n Museum(s) f i l e s . R esearch p r o je c t f i l e s . T his form i s a v a ila b le from and the Voucher No. i s a ssig n e d by th e Curator M ichigan S ta te U n iv e r s ity Entomology Museum. 127 Number o f : oo 3 CD I to 3* (0 00 Label data fo r specim ens c o lle c t e d or used and d e p o site d S p e c ie s or o th er taxon Pseud oletia unipuncta (Haworth] Michigan S t a te University campus, lab c u lt u r e Apanteles m i l i t a r i s Walsh Michigan S t a te University lab c u l t u r e reared from local popu­ l a t i o n s of Pseudoletia uni­ puncta (Haworth). 1977-1982, A. E. Rolim Q. O M to CO CD e CO I CO 3 40 M.S.U. 1 'ia 1 via M.S.U. to 00 id Michigan S t a te University lab c u l t u r e from Lahore, Pakistan, CIBC-PAK-77-1128. BIRL-77-58. From Agrotis sp. Apanteles r u f i c r u s Haliday s r^t S* ( t £. ff C i t t i (t in Tcto) 1 Via 1 M.S.U. o t-n Via to to CM to CO (Use a d d itio n a l s h e e ts i f n e c essa ry ) I n v e s t ig a t o r 's Name(s) (typed) Antonio Edilton Rolim__________ *cocoons Voucher No. 1983-2 R eceived the above l i s t e d specim ens fo r d e p o s it in the M ichigan S ta te U n iv e r sity EntomoJjegy Museum. -2. Date June 1983 urator 2 Dat?/ /f /3 < o e n 3* to T3 T3 CD CD 3 CL to - j . n X H3 *—* to 9 * rt to I—* ro 00 APPENDIX 2 Appendix 2 Tab le A. F ie ld Releases o f A. r u f ic r u s A d u lts and M a s s -P a ra s itiz e d Armyworm Larvae in M ichigan (1 9 7 8 ) Date Release Site Approximate Number Released Wasps Armyworms T4N R2W Sec 36 * 400 - T6S R7E Sec 25 (?) T4N R2W Sec 36 * 200 500 400 1000 7-02 Ib id . 200 04 Ib id . 400 500 - 15 Ib id . 600 - 19 T1S R9W Sec 9 800 - 21 200 600 500 - 27 T4N R1W Sec 19 * T1S R9W Sec 9 T4N R1W Sec 19 * 200 500 29 T4N R2W Sec 36 * 200 500 8-03 Ibid. 400 1000 08 I b id . 200 500 19 T4N R1W Sec 19 * 100 500 20 I b id . 200 500 25 I b id . 200 500 T4N R2W Sec 36 * 600 1000 17 Ibid . 400 1000 27 I b id . 100 500 10-04 I b id . 600 1000 7000 10000 6-13 22 29 26 9-08 T o ta ls *MSU Campus. 130 Appendix 2 Tab le B. F ie ld Releases o f A. r u f ic r u s A d u lts and M a s s -P a ra s itiz e d Armyworm Larvae in M ichigan (1 9 7 9 ) Date Release Site Approximate Number Released Wasps Armyworms 6-26 T4N R1W Sec 19 * 100 500 7-02 T4N R2W Sec 36 * 200 1000 11 T8N R3W Sec 25 200 1000 14 T4N R1W Sec 19 * T4N R2W Sec 36 * 200 500 200 500 T4N R1W Sec 30 * T4N R1W Sec 19 * 400 1000 100 500 T4N R2W Sec 36 * T4N R1W Sec 30 * 600 1500 400 1000 ■k 400 1000 20 8-05 07 20 31 9-03 T4N R2W Sec 36 10 Ibid. 800 1500 12 T4N R1W Sec 30 * 400 1000 14 Ibid. 200 1000 17 T4N R2W Sec 36 * 200 500 22 Ibid. 400 1000 26 Ibid. 400 1000 T4N R1W Sec 19 ★ T4N R2W Sec 36 * 200 500 400 500 5800 15500 10-03 09 Tota ls *MSU Campus. 131 Appendix 2 Table C. F ie ld Releases o f A. r u fic r u s A d u lts and M a s s -P a ra s itiz e d Armyworm Larvae in M ichigan (1 9 8 0 ) Date 6-17 23 7-08 Release Site Approximate Number Released Wasps Armyworms T8N R3W Sec 25 200 1000 T4N R2W Sec 36 * 100 1000 T8N R3W Sec 25 2000 - 12 Ib id . 500 1000 22 T4N R2W Sec 36 * 100 1000 25 T8N R3W Sec 25 100 1000 28 Ib id. 1000 2000 T4N R2W Sec 36 * 1000 - 12 I b id . 1000 - 16 Ib id. 500 1000 27 Ib id. 1000 3000 9-05 Ibid . 500 2000 12 I b id . 100 1000 21 Ib id . 200 1000 29 Ib id. 1000 500 10-05 Ibid. 2000 500 11 Ibid . 2000 1000 18 Ibid. 2000 1000 15300 18000 8-05 T o ta ls *MSU Campus