EFFECTS OF SOME PHYSICAL AND
BIOLOGICAL FACTORS ON THE
REPRODUCTION, DEVELOPMENT,
SURVIVAL AND BEHAVIOR OF THE
CEREAL LEAFBEETLE,
OuIema Meianopus (Linnaeus),
UNDER LABORATORY CONDITIONS

Thesis for the Degree of Ph. D.
MICHIGAN STATE UNIVERSITY
YOUNG MOK YUN
1967

III IIIIIIIIIIIIIIIIII

32 3121

A... III IIIIIIIIIIIIIIIIIIIIII

31

This is to certify that the
thesis entitled

EFFECTS OF SOME PHYSICAL AND BIOLOGICAL FACTORS ON THE
REPRODUCTION, DEVELOPI‘IENI‘, SURVIVAL, AND BEHAVIOR OF
THE CIIREAL LEAF BEETLE, Oulema melanopus (Linnaeus),
UI‘TDER LABORATORY CONDITIONS.

presented by

Young Mok Yun
has been accepted towards fulfillment

of the requirements for

J19.— degree in my

%/ 1/ CAM“

Prof. whamm—

Major professor

Date November 16, 1967

0-169

LIRPADV
Mg 1’; ‘9 .3

UniVCIuCy

  
 
  
 

   
 
  

amomc av V

RB & SONS'
K BINDERY IIIII.

may emoans
mm

 

" Q33
5%".

 

ABSTRACT

EFFECTS OF SOME PHYSICAL AND BIOLOGICAL FACTORS ON THE REPRODUCTION,
DEVELOPMENT, SURVIVAL, AND BEHAVIOR OF THE CEREAL LEAF BEETLE,
Oulema melanopus (Linnaeus), UNDER LABORATORY CONDITIONS

by Young Mbk Yun

From June 1964 to December 1966, a series of laboratory studies
were conducted to investigate the effects of various physical and
biological factors on the reproduction, development, survival, and

behavior of the cereal leaf beetle, Oulema melanopus (Linnaeus).

 

Diapause development in the summer adults seems to be completed
after 90 days of storage at 38° F. in the laboratory. The free flight
by the overwintered adults occurred at 68° F. and a minimum of 55° F.
seems to be required for an effective initial mating and egg deposition.
More consistent egg laying was observed when the temperature reached
70° F. or more.

After 110 days of storage at 38° F., one laboratory-reared
female laid 1,251 eggs over a period of 153 days in a lamp chimney
cage. A field-collected active spring female laid 256 eggs during a
‘28-day period under the same laboratory conditions. An isolated
virgin female laid 129 eggs but none of them hatched.

Optimum environmental conditions for the active spring adults
seem to be 80° F., 95 to 100 percent relative humidity, and an 18-hour

light period. Over 93 percent of the eggs were deposited during a

Young Mbk Yun
16-hour light period and only 7 percent during an 8-hour dark period
under laboratory conditions.

The cereal leaf beetle was able to complete its development
within a temperature range of 58° F. to 90° F. A more complete range
of temperature for the development is estimated to be between 54° F.
and 92.5° F. Thresholds of development were calculated as 52° F. for
the egg, 46.6° F. for the larva, 54° F. for the pupa, and 51.6° F. for
the entire immature stage. A complete development from an egg to
adult requires an average of 92 days at 58° F., 52 days at 670 F.,

28 days at 80° F., and 23 days at 90° F. Davidson's (1944) logistic
and linear regression equations were used to express the relationship
between temperature and the rate of development in the eggs, larvae,
pupae, and entire immature stages.

The overwintering adults seemed to be the most resistant of all
stages against the cold followed by eggs, pupae, larvae, active summer
adults, and lastly by active spring adults. The inactive summer adults
were the most resistant stage to the high temperatures of 110° F. and
120° F. followed by larvae, eggs, pupae and active summer adults, and
by spring adults.

Treatments of the summer adults with various combinations of
temperature and light period have failed to break diapause in this
beetle. Some of the early eggs laid by the summer adults were sampled
and raised to adults for three consecutive generations, but no apparent
non-diapausing strain of the beetle was detected.

Age-specific life and fertility tables were constructed for the

laboratory and field populations of the cereal leaf beetle. Out of

Young Mok Yun
1,000 eggs, 202 adults that are comparable to the spring adults sur-
vived after 90 days of storage at 38° F. Based on the 90-day storage
period at 38° F., the net reproduction rate for the laboratory popula-
tion was calculated as 3.94. The net reproduction rate of the field
population was estimated at 0.94 when the field mortality data of

Dr. R. F. Ruppel were applied.

EFFECTS OF SOME PHYSICAL AND BIOLOGICAL FACTORS ON THE REPRODUCTION,
DEVELOPMENT, SURVIVAL, AND BEHAVIOR OF THE CEREAL LEAF BEETLE,

Oulema melangpus (Linnaeus), UNDER LABORATORY CONDITIONS

 

BY

Young Mbk Yun

A THESIS

Submitted to
Michigan State university
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Entomology

1967

.“'l
."1
-2‘

J

ACKNOWLEDGEMENT

I am grateful to Dr. Gordon B. Guyer, Chairman of the Department
of Entomology, for his constant encouragement and support throughout
the entire period of this study.

My sincere appreciation is extended to Dr. Robert F. Ruppel
under whose guidance this study was initiated and to Professor
Richard V. Connin under whose constant supervision this investigation
was successfully undertaken and concluded.

Special thanks are expressed to Drs. James W. Butcher and
Dean L. Haynes of Entomology Department and Dr. Fred C. Elliott of
Crop Science Department for their valuable suggestions and criticism.

I am also indebted to Messrs. David L. Cobb and George Lawson
of Entomology Research Division, U.S.D.A., and to Messrs. John C.
Arnsman and Melvin S. Gomulinski of Michigan State University for
their aid in accomplishing this study.

My appreciation is further extended to Dr. Reynold G. Dahms of
Entomology Research Division, U.S.D.A., for providing necessary funds
and facilities for conducting this investigation, and also to
Mr. Maurice E. TUrner of Plant Pest Control Div., U.S.D.A. and
Messrs. Dean F. Lovitt, John C. Dreves, and Howard Martin of Michigan
Department of Agriculture for furnishing valuable information regarding
infestation and distribution of the beetle.

Finally my thanks are due to Mrs. Arthur L. Wells for typing
this thesis.

ii

TABLE OF CONTENTS

Page
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . l
DISTRIBUTION AND ECONOMIC IMPORTANCE . . . . . . . . . . . . . . 3
LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . 7
OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

EXPERIMENTAL PROCEDURES AND RESULTS . . . . . . . . . . . . . . 22
Influence of Physical Factors . . . . . . . . . . . . . . . . 22
Influence of Biological Factors . . . . . . . . . . . . . . . 63
Diapause Studies . . . . . . . . . . . . . . . . . . . . . . 86
Life Tables and Net Reproduction Rates . . . . . . . . . . . 107
General Behavior and Sex Ratio . . . . . . . . . . . . . . . 114

DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . 146

iii

Table

10.

ll.

12.

13.

LIST OF TABLES

Total number of counties infested with the cereal
leaf beetle by state and year . . . . . . .

Summarization of published life cycle statistics

Duration of development and mortality of the cereal
leaf beetle at various constant temperatures .

Number of days required for a complete development
(y) and the speed of development in terms of
percent development in one day (100/y) of egg,
larva, pupa, and entire immature stages of the
cereal leaf beetle at different constant
temperatures . . . . . . . . . . . .

Logistic curve and straight line equations for the
development of different stages of the cereal
leaf beetle

A comparison of observed and calculated 100/y values

Calculated thresholds for development of the cereal
leaf beetle using two different methods . .

Egg production at 80° F. and 85° F. by the adults
that had been stored for 50 days at 38° F.--
Test 1 . . . . . . . . . . . . . . . . . . . .

Egg production at 80° F. by the adults that had been
stored at 38° F. for 90, 155, and 250 days--
Test 2 . . . . . . . . . . . . . . . . . . . . .
Development of pupae at 80° F. and 85° F. . . .

Number of adults obtained from larvae reared on oats
and barley at 73° F. and 800 F. . . . . . . . .

Egg production by overwintered adults under constant
80° F. and fluctuating day and night temperatures

Percent mortality of eggs, larvae, pupae, and adults
at various extreme temperatures

iv

Page

24

26

31

32

35

37

38

39

40

42

44

LIST OF TABLES--Cont.

Table Page
14. Egg production under different photoperiods during
a 56-day test period--Test 1 . . . . . . . . . . . . . 47
15. Egg production under l4, l6, and 18 hours of photo-
periods during a 63-day test period--Test 2 . . . . . 48
16. Development of eggs, larvae, and pupae under
different photoperiods . . . . . . . . . . . . . . . . 51
17. Number of eggs laid during day and night hours for
a 10-day period on oats . . . . . . . . . . . . . . . 52
18. Egg production under different relative humidities . . . 54

19. Development of pupae and emergence of adults from
larvae that were allowed to pupate in the soil
with different moisture contents—-Test l . . . . . . . 56

20. Emergence of adults from pupae that were placed on
white sand with different moisture contents--
Test 2 . . . . . . . . . . . . . . . . . . . . . . . . 57

21. Emergence of adults from pupae that were suspended
above white sand with different moisture contents--
Test 3 O O O O O O O O O O O O O O O O O O O O O O O O 58

22. Oviposition of eggs on oat seedlings planted in
different types of soil . . . . . . . . . . . . . . . 59

23. Development of pupae and emergence of adults from
larvae in different types of soil . . . . . . . . . . 60

24. Effect of different cage sizes on egg production by
field-collected beetles stored in the laboratory

and by field-collected active spring adults . . . . . 63
25. Effect of different larval densities on development

of larvae through to the adults . . . . . . . . . . . 65
26. Relationship between larval density and mortality . . . . 66

27. Total number of eggs laid per cage and that per
female at different adult densities--Test l . . . . . 70

28. Total number of eggs laid per cage and that per
female at different adult densities--Test 2 . . . . . 71

29. Total number of eggs laid per cage and that per
female at different adult densities--Test 3 . . . . . 72

LIST OF TABLES—-Cont.
Table

30. Amount of feeding, egg production, and survival of
cereal leaf beetles stored at 43° F. for 65 days .

31. Oviposition of eggs on oats and barley by female
cereal leaf beetles

32. Oviposition of eggs on oat seedlings of different
heights and densities

33. Fecundity of females in cages with different male-
female combinations

34. Fecundity of field-collected active spring females
in cages with different male-female combinations .

35. Number and percent of cereal leaf beetle eggs con—
sumed by a coccinellid predator

36. Egg production by newly emerged summer adults after
a brief exposure to extreme temperatures .

37. Egg production by field-collected summer adults after
an exposure to low temperatures for 30 days . .

38. Egg production by summer adults after varying periods
of storage at 38° F. . . . . . . . . . . . . .

39. Total number of eggs laid by isolated pairs and
isolated females .

40. Ninety—five percent confidence limits for the mean
egg production per female

41. Observed and calculated time-mortality relationship
for the summer adults stored at constant 38° F.

42. Empirical time-mortality values for the summer adults
stored at 38° F.

43. Egg production by newly emerged summer adults under
different photoperiods during a 38-day test
period . .

44. Egg production by newly emerged summer adults for
three continuous generations under different
light periods

45. Egg production by the summer adults in the laboratory
and natural environment with and without hiding

places .

vi

Page

77

78

79

81

81

85

87

89

91

93

95

98

100

102

104

106

LIST OF TABLES-~Cont.
Table

46. Age-specific life table for the cereal leaf beetle
under laboratory conditions . . . . . . . .

47. Age-specific life and fertility table for the cereal
leaf beetle that had been stored at 38° F. for 90
days in the laboratory . . . . . . . . . . . . .

48. Age-specific life and fertility table for the field
population using field mortality data . . . . . .

49. Number and percent eggs occurring in different numbers
on different parts of oat and barley leaves .

50. Oviposition of eggs on upper and lower surfaces of oat
leaves with different leaf postures . . . .

51. Sex ratios of field-collected and laboratory-reared
spring and summer adults .

vii

Page

110

112

113

118

120

121

Figure

10.

LIST OF FIGURES

Spread of the cereal leaf beetle in the United States
from 1962 through 1967 .

Temperature-time (closed circle) and temperature-
velocity (open circle) curves for the egg stage

Temperature-time (closed circle) and temperature-
velocity (open circle) curves for the larval
stage . . . . .

Temperature-time (closed circle) and temperature-
velocity (open circle) curves for the pupal stage

Temperature-time (closed circle) and temperature—
velocity (open circle) curves for the entire
immature stage . . . . . . . . .

The rate of development of egg, larval, pupal, and
entire immature stage at different constant
temperatures .

Mean total number of eggs laid per 15 females under
l4, l6, and 18 hours of light periods

Relationship between larval density and mortality .

Mean total number of eggs produced per combination
(a) and that per female (b) in cages with
different male-female combinations in previously

mated and unmated adults .

Observed and empirical time-mortality relationship for
the summer adults stored at constant 38° F.

viii

Page

27

28

29

30

34

49

67

82

99

INTRODUCTION

The cereal leaf beetle, Oulema melanopus (Linnaeus), is one of

 

the oldest pests of small grains in the Old World. In the united
States, the pest was first reported in 1962 from Berrien County,
Michigan. Numerous individual and cooperative research projects have
been set up and carried out by investigators in Michigan, Indiana,
Ohio, and U. S. Department of Agriculture. Major areas of studies

were on biology, ecology, host plant resistance, and chemical and
biological control of the pest. During the five-year period from 1962
to 1967 these investigators have produced a large amount of information
regarding various aspects of the beetle.

In spite of the large—scale chemical control effort, the popu-
lation has increased and continued to spread. The pest was first
found in Ohio in 1963 (USDA, 1963), in Illinois in 1965 (USDA, 1965),
and in Pennsylvania in 1967 (USDA, 1967). In 1965 the pest was also
found in Ontario, Canada (personal communication with Mr. Maurice E.
Turner of Plant Pest Control Division, USDA).

European literature on the cereal leaf beetle is rather limited
and observations and results are often incomplete and inconsistent.
Apparently no systematic studies on this pest have ever been carried
out in Europe. Most European papers are simple records of field and
laboratory observations. The natural history of the cereal leaf beetle
has been described and a brief outline of the life cycle of the pest
is given in some European literature.

1

2

Systematic studies on the natural history of the cereal leaf
beetle in the united States were initiated by Guyer (1962), Ruppel
(1964), Castro (1964), and Castro, e£_al: (1965). The information ob-
tained from these studies will be extremely useful in later studies on
population dynamics, host plant resistance, and optimistically the
eventual control of the pest. Their research, however, consisted
largely of field studies and many specific questions regarding biology
and ecology of the cereal leaf beetle are still left unanswered.

The author conducted a series of studies on the reproduction,
growth, and survival of the cereal leaf beetle under various laboratory
conditions during the two and a half year period from 1964 to 1966.
Laboratory results were compared with field observations wherever it
was feasible. It is hoped that the information obtained from this
study will be useful in future studies on biology, ecology, and control

of the pest.

DISTRIBUTION AND ECONOMIC IMPORTANCE

The cereal leaf beetle has been known as a pest of small grains
in Europe since at least 1737 (Kadocsa, undated). According to the
available literature from Europe, the beetle is distributed throughout
the humid and subhumid regions of the western Paleoarctic zone. This
area roughly covers the whole continent of Europe, parts of northern
Africa, Iran, Turkey, and central Siberia eastward (Hodson, 1929;
Balachowsky and Mesnil, 1935; Urquijo, 1940; Venturi, 1942; Sengupta
and Behura, 1957; USDA, 1958; and Balachowsky, 1963).

The pest is generally considered as scarce and sporadic through-
out most of the range. However, more frequent and severe damage to
small grains has been recorded in the region of the Balkans, the
Ukraine and the Transcaucasia area of the Soviet Union. This region '
has a continental climate and the abundance of the beetle is apparently
favored by an early warm spring followed by a relatively dry summer
(Kadocsa, 1916; Balachowsky and Mesnil, 1935 and Urquijo, 1940).

The cereal leaf beetle was first identified in the United States
in July of 1962 from specimens collected in Berrien County, Michigan.
How and when the pest reached the southwestern corner of Michigan is
still not known. A few farmers in Galien, Michigan reported that they
sprayed their oat fields as early as 1959 to control the then uniden-
tified pest. The infestation of the pest and damage to the small
grains, especially spring-planted crops, became heavier and heavier

3

4

during the subsequent years (unpublished survey report by Michigan
Department of Agriculture, 1962).

A survey conducted in summer of 1962 indicated that Berrien and
Cass Counties in Michigan and adjacent St. Joseph and LaPorte Counties
in Indiana were infested with the cereal leaf beetle (USDA, 1962).
The beetle was first found in Ohio in 1963 (USDA, 1963) and the in—
fested area has continued to expand mainly to the north, east, and
south following the directions of prevailing winds. The pest has moved
westward into Illinois in 1965 (USDA, 1965). In the same year the
beetle was discovered for the first time in Harrow and Essex Counties
in Ontario, Canada (personal communication with Mr. Maurice E. Turner
of Plant Pest Control Div., ARS, USDA, Lansing, Michigan). The pest
has moved further eastward into Pennsylvania in 1967 (USDA, 1967),
The number of counties infested with the beetle in five states is
given in Table l and the general distribution of the pest in the United
States from 1962 through 1967 is shown in Figure l. The population
density of the cereal leaf beetle is still highest around the original
sites of infestation in 1962, namely southwestern Michigan and adjacent
counties in northern Indiana.

The actual yield reductions caused by spring adults and larvae
of the pest have been estimated at 12 to 28 percent in winter wheat
and 15 to 35 percent in spring oats and barley. It is also estimated
that in Michigan, a minimum annual loss of 1.93 million dollars from
the beetle damage can be expected in the areas where the beetle popula—
.tion is high. An annual loss of as much as 11.85 million dollars can
be expected if the pest becomes established in the entire state (from

unpublished data by Dr. R. F. Ruppel in 1965).

TABLE 1.-—Tota1 number of counties infested with the cereal leaf beetle
by state and year (from USDA 1966b and 1967)

Total Number of Counties Infested

 

 

State 1962 1963 1964 1965 1966 1967
Michigan 2 15 34 43 53 60
Indiana 2 25 32 38 54 65
Ohio 0 l 18 49 63 83
Illinois 0 0 0 3 3 6
Pennsylvania 0 0 0 0 0 4

 

Total 4 41 84 133 173 230

 

VD
Ill/ll/Il/III

IIIOOOIOIOIOO
O O O O
‘I D 'I 9 VI ’
Ill!

’

NIGHT H N

 

        

n“;

‘v‘
n a

it 1‘.
1w

III/III]!
oooooooooooJ/ I I II I III
oooooo’l/l/IIIII/

ll

       
  

    
  

     

lNDIAN

2 3 4 5
6 6 6 6
0.. 9 9 9
1 l 1 l

énuuuxuuum .

y//

 

      

noon/III"
.
nuns/III"...H

      

n‘ea....l..

one/III.
o oil/I.

1966

 

ited States from 1962 through 1967.

Fig. l - Spread of the cereal leaf beetle in the Un

LITERATURE REVIEW

The general life cycle of the cereal leaf beetle, Oulema
melanopus (Linnaeus), has been described to various extents by workers
in Russia (Megalov, 1925; and Vassiliev, 1913), Rumania (Manolache,
1932; and Knechtel and Manolache, 1936), Hungary (Kadocsa, 1916),
Italy (Venturi, 1942), France (Mesnil, 1931; Balachowsky and Mesnil,
1935), Sweden (Borg, 1959), Spain (Urquijo, 1940), Great Britain
(Hodson, 1929), and more recently in the United States (Guyer, 1962;
Castro, 1964; and Castro, g£_313, 1965). Some of the results of these
studies on the biology of the cereal leaf beetle are summarized in
Table 2. Other articles that have been published in the United States
and describe at least a part of the biology of the cereal leaf beetle
include Favinger (1962), Castro and Guyer (1963), Ruppel (1964),
Ruppel and Castro (1964), Shade and Wilson (1964), Wilson and Ruppel
(1964), Wilson and Shade (1964 a and b; 1966), Janes and Ruppel (1965),

Connin, g£_gl, (1966a), and Connin, 35.31: (in press).

Overwintering

 

The available literature from Europe and the United States
notes that the cereal leaf beetle overwinters as an adult in forest
litters, grasses, tree bark, in any small crevice, or in a variety of
tight places that are protected from excessive heat and cold (Hodson,
1929; Balachowsky and Mesnil, 1935; Knechtel and Manolache, 1936, and

7

 

A.mooeva~zma

 

 

meme nmm.wm crammo A.moomvma-ma A.eoomvmaua A.moomvaze A.moowvooezoma cmmflnuaz
ammo .«nm: nm-o~ ONINH nHIA onauooa sacrum
amen .waom e-m seesaw
mama .Atsuca> No-oe nNION AamzveHINH AmszmIN
A.Aa<Vo~ A.Aa<va oma-ooH NHIm AHAOH
oamfi .OHMDqu mm Camam
emma .meumaocmz
mam Hancooax A.mommvmm
A.aow.mnvo A.eowevam A.mom.mevm
A.eoowvm A.mo~.mavma A.eoemva
meIOe ma-ea mHIeH NHIOH oma-om wHIN massage
mmaa .Haammx
cam hxm3onomfimm mm ma mum museum
mmaa .a0meom onIme ONIAH ea-ma mH-HH om mud cfimafium
awed
e mama .>oamwmz NSImm ma-eH mH-~H «HImH «amaze
acumwfiumo>cH amDOH maam m>umq wwm acmmmm Mom moo Ham muucaoo
mamaom\ mamaom\
when CH mowmum mo aofiuwuon wwwm .oz wwwm .oz

 

 

mowumaumum macho swag oozmfiansm mo :oHumNHumaaamll.N mqm<H

9
Castro, 35 31., 1965). An overwintering experiment by Castro (1964)
shows that the lowest winter mortality was observed among experimental
adult beetles placed at ground level.

Laboratory studies indicated that the diapausing adults could
be held at 43° F. for a considerable period of time. The mortality of
the adults at 43° F. ranged from 1 to 5 percent after 70 days, 30 per-
cent after 90 days, 39 percent after 120 days, 50 percent after 160
days, and 65 percent at the end of 190 days. The beetle survived much
better when they were provided with water (Castro, g£_§1:, 1965).

Further laboratory studies by Castro (1964) showed that the dia-
pausing adults, after a 20—day holding period at 43° F., suffered
3 percent mortality after 10 days and from 9 to 10 percent mortality
after 25 days at 25° F. At 15° F., after 20 days of storage period at
43° F., there was 17 percent mortality after 10 days, 32 percent after
15 days, and 100 percent mortality at the end of 20 days. At 0° F.,
there was 22 percent kill of the adults after 3 days, 91 percent after

7 days, and 100 percent mortality after 10 days at 0° F.

Sprinngdults

 

The overwintering adults become active in April or May when the
mean daily temperature reaches 50° F. (Knechtel and Manolache, 1936).
In Michigan, the adults emerge from their hibernation sites during the
first warm days of late winter or early spring. The first active adults
were found as early as the 4th of March in 1964 by Mr. N. Remington of
the Michigan Department of Agriculture. The adults seem to be active

when temperature reaches 55° F. or more (Castro,_§£”al., 1965).

10

The flight of the adult beetles is said to occur freely at 62° F.
by Hodson (1929) or at 62.6° F. by Balachowsky (1963). The greatest
amount of flight was observed in the field in late April when tempera-
tures were 72° F. and up to 880 F. at the plant level (Castro, et_al:,
1965).

Several workers have indicated that the cereal leaf beetle shows
marked preferences for host plants. Gallun and Ruppel (1963) found
more eggs on oats and barley than on wheat during their host resistance
studies near Galien, Michigan. Wilson and Shade (1964a) reported that
oats were preferred to barley or wheat for oviposition. Castro,_g£.al.
(1965) mentioned that oats and barley were more severely damaged by
all stages of the beetle than were wheat and grasses. Most reports
from Europe state that succulent spring grains are more attractive to
the spring adults than winter crops.

The overwintered adults mate in 4 to 5 days and the first eggs
are laid about a week after the mating (Hodson, 1929; and Knechtel
and Manolache, 1936). The mating takes place without any special
courtship behavior and it may last for several hours. Multiple mating
seems to be the rule in this species (Castro, 25.31:: 1965; and
Merino M., 1966). Merino M. (1966) also stated that definite homo-

sexual behavior exists in the males of this species.

Oviposition

The eggs of the cereal leaf beetle are usually laid one or two
at a time on the upper surface of the leaves of host plants (Balachowsky
arui Mesnil, 1935; and Castro, 1964). Castro (1964) reported that 98.5

pernzent of the eggs were found on the upper surface, 59.8 percent in

11

the basal third region of the leaf, and 83.9 percent of the eggs
occurred either singly or in pairs. Castro, e£_§13 (1965) noted that
the greater number of eggs were laid on plants 4 to 4-3/4 inches tall.

One female beetle in spring lays l to 3 eggs a day in England
(Hodson, 1929), an average of 3 eggs and up to 12 eggs per day in
Italy (Venturi, 1942), 5 to 6 eggs per day in Sweden (Borg, 1959), and
2 to 18 eggs per day in Rumania (Knechtel and Manolache, 1936). The
oviposition activity continues for 45 to 60 days and during this period
one female lays up to about 50 eggs in England (Hodson, 1929), 100 to
150 eggs in Italy (Venturi, 1942), 50 to 150 eggs in Rumania (Knechtel
and Manolache, 1936) and an average of 96 eggs in Michigan (unpublished
data by Dr. R. F. Ruppel of Michigan State University). In the
laboratory, however, the total egg production was estimated to be 150
to 400 eggs per female (Castro, 35.2l3’ 1965). Hodson (1929) stated
that a single mating is sufficient for a female to lay fertilized eggs
for several weeks. The eggs are observed in the field from April to
as late as 19th of July in Europe. Some of the spring adults can sur-
vive for two years and may deposit some eggs during the second season

(Megalov, 1927; and Hodson, 1929).

Egg
As Table 2 indicates, the incubation period for the egg ranges
from 7 to 15 days in the field. Knechtel and Manolache (1936) re-
ported that the threshold for development of the egg is 53.6° F. The
eggs would fully develop in 4 days at 86° F., 8 days at 69.8° F., and
23 days at 59° F. Castro (1964) stated that the eggs hatched in 4 to

7 (iays at 75° to 800 F., 13 to 21 days at 60° F., and there was no egg

12
hatching at a constant 500 F. with 16 hours of light and 60 percent
relative humidity. Total egg hatching at 80:3° F. ranged from 62 to
over 80 percent.
In the field, the egg mortality was about 50 percent in winter
wheat and 10 percent in spring oats. The greater part of the egg
mortality was attributed to low temperatures but a considerable por-

tion of the kill was also due to a coccinellid predator, Coleomegilla

 

maculata lengi Timberlake (Castro, 35,313, 1965). The importance of

 

this lady beetle as a predator of the cereal leaf beetle eggs was also

mentioned by Yun (1964) and Yun and Ruppel (1964).

Lee:

Young larvae upon eclosion start feeding on the upper surface of
the larvae, leaving the lower cuticle largely intact. It was estimated
in the laboratory that one larva consumed approximately 119.35 mg. of
leaf tissue to complete its development while an adult consumed 25.9 mg.
of leaf tissue per day and the total amount of 1,040 mg. during its
40-day active period (Castro, gt 31., 1965).

As in the egg, the larval development also starts at 53.6° F.

according to Knechtel and Manolache (1936).

Pupa

Threshold for the development of the pupa is given as 48.2° F.
by Knechtel and Manolache (1936). It takes from 12 to 15 days for a
pupa to complete its development at 80° F. and only 40 to 60 percent of
the larvae that entered the soil for pupation emerged as adults (Castro,
-SE.EE:: 1965). Castro (1964) believes that the high pupal mortality

‘was largely due to an improper soil moisture content. The pupal

13
mortality was even higher in the field. The newly emerged adults
accounted for only 10 to 30 percent of the larvae that were present in

the field (Castro, e£_31: 1965).

Summer Adult

 

Mbst workers in Europe and the United States seem to agree that
new adults emerge from the soil in early to mid-summer and feed on
young succulent grasses for about two weeks. During this period the
summer adults are extremely active and some of them were caught at
1,000 feet in airplane traps (Wilson and Ruppel, 1964). Wilson and
Ruppel (1964) and Shade and Wilson (1964) assumed that wind-borne dis-
persion could be of great significance in this species.

Mesnil (1931) stated that some new adults emerge in summer while
others stay in the soil until the following spring. Vassiliev (1913)
and Vereshtchagin (1914), on the other hand, reported that all of the
new adults stay within the pupal cases in the soil until the following
spring.

The total developmental periods from egg to adult are given as
39 to 42 days in Russia, 40 to 45 days in Rumania, 40 to 62 days in
Italy, and 43 to 50 days in Britain (Table 2).

Although the males occasionally attempted to mate, no success-
ful mating of the summer adults was observed (Castro, 32 31., 1965).
Khmararaj (1964) and Hoopingarner, g£_§13 (1965) reported that the
gonads of the female do not normally develop until they have been
subjected to a low temperature for a certain period of time.

Mbst European literature indicates the presence of only one

gerueration per year in this species except Averin (1914) who claims

14

the existence of the second generation in Russia. Hodson (1929) and
Borg (1959) also mentioned the possibility of the second generation in
Great Britain and Central Europe. A group of field-collected summer
adults produced a second generation in the laboratory (Castro, 35 31.,
1965) and oviposition by summer adults in field cages was noted in
Indiana by Wilson and Toba (1963). In Michigan, however, the cereal
leaf beetle seems to have a univoltine life cycle with an obligatory

diapause in adult stage under field conditions (Castro, e£_al., 1965).

Diapause

Extrinsic and intrinsic factors that affect the onset and dura-
tion of diapause are: l) photoperiod, 2) temperature, 3) moisture,
4) diet, and 5) maternal physiology (Wigglesworth, 1953; Andrewartha
and Birch, 1954; Lees, 1955; de Wilde, 1962; and Harvey, 1962).

In the cereal leaf beetle, photoperiod studies in the laboratory
showed that some newly emerged adults mated and oviposited under a 16—
hour photoperiod in 15 days after their emergence from the soil.
Similarly treated adults, however, failed to reproduce under a 12-hour
light period. Exposure of immature stages to a 12-hour or 16-hour
photoperiod did not affect the reproductive behavior in the adult
stage. Diapausing beetles under a 12-hour light period started to lay
eggs when they were transferred to a 16-hour photoperiod. The cereal
leaf beetle seems to respond more readily to a long-day photoperiod of
16 hours than to a short-day lZ—hour light period (Castro, 1964;
Castro, £53., 1965).

The adults of Colorado potato beetle, Leptinotarsa decemlineata,

go :into diapause when they are exposed to a short photoperiod of 8 to

15
12 hours but they may be reactivated by a long photoperiod (de Wilde,

g£_§1:, 1959). In certain bivoltine races of Bombyx mori, nearly all

 

the females developed from eggs that had been exposed to a long photo—
period laid diapausing eggs; while the females developing from eggs
that were exposed to short days laid only non-diapause eggs (Kogure,
1933). In some cases diapause has been shown to be quite independent
from the photoperiod. Examples are the greenbottle fly, Lucilia

sericata, and vegetable weevil, Listroderes obliquus (Dickson, 1949).

 

Attempts to break diapause by subjecting the diapausing adults
to various cold temperatures for a short period of time failed to
yield satisfactory results. The diapausing adults were induced to
reproduce by subjecting them to 0° F., 15° F., 25° F., and 43° F. for
15 to 25 days but egg production was highly inconsistent. Mbre con-
sistent egg production was obtained when the adult beetles were placed
in a lamp chimney cage without any hiding places. Castro (1964)
doubted the effectiveness of such short-period cold treatments in
breaking diapause. The diapause seemed to be completely broken in
the beetles that were subjected to 43° F. for at least 100 days (Castro,
333., 1965).

In general, low temperatures favor the onset of diapause and
arrest of growth while high temperatures tend to avert diapause (Lees,
1955). In long—day insects, high temperatures are effective in re-
activating the diapausing insects (Way and Hopkins, 1950; and Beck and

Hanec, 1960). In the corn earworm, Heliothis zeae, diapause is induced

 

by low temperatures during larval stage (Ditman, EEUElsa 1940).
One of the surest ways to bring the diapause-stage to an end

is to expose the diapausing insects to adequate low temperature. With

16

many species, diapause—development proceeds most rapidly at some
temperature above 0° C. (Andrewartha and Birch, 1954).

The effect of moisture on diapause is apparently complicated.
Squire (1940) showed that diapause in the pink bollworm Platyedra
_gossypiella is induced by lack of moisture in the food. Andrewartha
(1952), however, stated "the evidence indicates that the absorption
of water during aestivation or hibernation is rarely if ever the
primary stimulus which initiates diapause-development".

Both quantity and quality of food substances apparently in-
fluence the onset of diapause in some insects. Diapause in the corn-

stalk borer, Diatraea lineolata (Pyralidae) is sometimes induced by

 

starvation (Kevan, 1944). The larvae of Euproctis_phaeorrhoea

 

(Lymantriidae) which normally go into diapause in the fall will com-
plete development without diapause if fed with tender apple foliage
(Grison, 1947).

The physiological constitution of the females of Bombyx mori

 

affect the diapause pattern of the following generation (Kogure, 1933).
The sensitive and responsive stage, therefore, may be far apart. In
addition to above mentioned factors, wounding or artificial shock
treatments such as electric shock, pricking with a needle, and dipping
in or exposure to certain chemicals are also proved to be effective
in reactivating some diapausing insects (Andrewartha and Birch, 1954).
Hibernation in univoltine species in a temperate climate is
usually preceded by a long period of aestivation. Actual diapause may
not necessarily be more intense than in multivoltine species which do
not aestivate. The longer dormant period in univoltine species may be

simply due to the fact that diapause—development does not take place

17

during the hot summer months. The diapause-development is usually
completed most rapidly during the autumn and winter (Zolotarev, 1947).

Diapause in insects is more recently recognized as an endocrine
deficiency syndrome of the prothoracic glands (Williams, 1956) or of
the corpora allata (de Wilde and Boer, 1961). In adult insects it is
characterized by an inhibition in the maturation of eggs associated
with corpus allatum failure (de Wilde and Boer, 1961). Mbre recently
Bowers and Blickenstaff (1966) reported that they found some inhibition
of corpus allatum development in diapausing alfalfa weevil. By applying
an active synthetic hormone exogenously, they were able to terminate
diapause in the weevil. Using the same methods, Connin, st 31. (in

press) were also able to break diapause in the cereal leaf beetle.

Temperature-Development Relationship

various mathematical formulae have been proposed and used by
biologists to describe the relationship between temperature and speed
of development in insects and other related animals. The relationship
has been reviewed to various extents by Crozier (1926), Shelford (1929),
Belehradek (1930), UVarov (1931), Janisch (1932), Hoskins and Craig

(1935), Huffaker (1944), Davidson (1944), Fry (1947), Wigglesworth
(1953), Andrewartha and Birch (1954), and Messenger and Flitters
(1958).

Davidson (1942 and 1944) proposed the use of the logistic
equation to show the relationship between temperature and the time
required for development in insects and other poikilothermic animals.
Thi: equation given below represents a form of the logistic curve

Originally developed by Pearl and Reed (1920).

1_ K
y 1 + e8 - bx

 

1/y is the reciprocal of the time required for a given stage of an
insect to develop at a given temperature x; K, a and b are constants.
The calculated values for l/y, when plotted against appropriate values
for temperature (x) describe an S-shaped velocity curve, and the value
for K represents the upper asymptote of the curve.

Davidson (1944) claims that this curve faithfully represents
the trend of the speed of development of insects for 85 to 90 percent
of the complete range of temperature at which development can go on.
This formula apparently gives the most adequate empirical description
of the temperature-development relationship that has so far been sug-
gested (Wigglesworth, 1953; and Andrewartha and Birch, 1954).

Uvarov (1931) developed the following formula for calculating
the theoretical threshold of development from experimental data.

dt - DT
d - D

K =
K is the threshold of development, t and T are constant temperatures
within the optimum range of development and d and D are the respective
durations of the stage of insect at the constant temperatures t and
T. Theoretically, the point where the velocity line or rate-of-

development line crosses the temperature axis is also the threshold

of development (Matteson and Decker, 1965).

Intraspecific Competition

 

Klomp (1964) listed the four major requisites in short supply
for which the animals compete as 1) food, 2) oviposition sites, 3)

space, and 4) cover.

19
Competition for food is regarded as the most common type of
competition. It has been reported to occur among the larvae (Sang,
1949) and adults (Robertson and Sang, 1944; and Chiang and Hodson,

1950) of Drosophila. Competition for oviposition sites has been

 

observed in Callosobruchus weevil where an increasing density of

 

adults induces a decline in the rate of oviposition (Utida, 1941).
Competition for space has been observed in the larvae of

Callosobruchus weevil where the larvae start to destroy each other when

 

density reaches about five individuals per bean (Utida, 1942). Several
authors indicated that competition for cover may occur when the number
of covers or hiding places is limited during periods of unfavorable
weather (Smith, 1935; Andrewartha and Birch, 1954; and deBach, 1958).
Pearl and Parker (1922) observed that the rate of reproduction

in Drosophila melanogaster Meig. was highest at the lowest density and

 

it gradually declined as the density increased. Using Chapman's
(1928) data on the rate of increase in laboratory populations of

Tribolium confusum Duv., Allee (1931) found that the rate of increase

 

of population per female day was greatest at the second lowest density.
The consequences of increasing intensity of competition among adult
insects that are most frequently mentioned in the literature are

l) decreasing fecundity or oviposition rate, 2) increasing emigration
rate, and 3) decreasing longevity.

The main causes of a decrease in the net reproduction rate with
increasing adult density are due to 1) increased egg cannibalism in
the adults of Tribolium sp. (Chapman, 1928; and Park, 1932 and 1933),
2) a decrease in the rate of copulation and a disturbance of the ovi-

position act (McLagan, 1932), and 3) an excessive contact between

20
individuals, reduction in the amount of food available to individual
animals, and conditioning of the medium by the accumulation of various
metabolic waste products (Crombie, 1942).

Crombie (1944) and Andersen (1960) stated that in general an
increasing competition among larval insects would result in 1) reduc-
tion of size or weight of larvae, pupae, and adults, 2) increase of
the mortality rate among larvae and pupae, 3) increase or decrease in
the rate of development of immature stages and of the longevity in
adults, and 4) change of sex ratio.

Klomp (1964) concluded that competition is of minor significance
in the regulation of density of phytophagous insects. It is almost
only during heavy infestation of pests that this process is responsible

for a decline in numbers.

Life Table

 

The use of life tables has become a common practice among popu-

lation ecologists to describe and understand the population dynamics

of a species. The methods for preparing such life tables are given by
Deevey (1947), Morris and Miller (1954), and Southwood (1966), and
further examples can be found in articles on spruce budworm populations
by Morris (1963) and on winter moth by Embree (1965). Calculations for
the net reproduction rate and the intrinsic rate of natural increase
are described in detail by Birch (1948), Laughlin (1965), and Southwood

(1966).

OBJECTIVES

As the title indicates the main objectives of this study were
to investigate and obtain more complete information regarding the
effects of various physical and biological factors on the reproduction,
development, survival, and behavior of the cereal leaf beetle.

Included in this study are temperature-development relationship,
influence of light, relative humidity, and soil factors, determination
of thresholds and optimal physical environment, effect of these
physical factors on induction and termination of diapause, effect of
density and host plant factors, construction of life tables, and
general behavior of the beetle under controlled environmental condi-
tions.

It is hoped that the information obtained from this study would
provide more complete knowledge of the species itself and it would

also facilitate future quarantine and control programs.

21

EXPERIMENTAL PROCEDURES AND RESULTS

Influence of Physical Factors

 

For an effective presentation of the results, the physical
factors presented in this chapter include "non-living" factors such
as temperature, light, moisture, soil, and space. In this part of
study, the author was mainly interested in the direct influence of
various physical factors on the speed of development, fecundity, and
longevity of the cereal leaf beetle.

Experiment 1. Rate of Development at various Constant Temperatures

and Thresholds for Development of Different Stages of
the Cereal Leaf Beetle

 

 

 

 

Methods: In order to investigate the time-development relation—
ship of the cereal leaf beetle at various constant temperatures and to
determine the thresholds and optimal temperature range for the develop-
ment of the beetle, the following procedures were employed. Fresh eggs
less than 24-hour old were obtained from the cereal leaf beetle rearing
program (Connin, §£_gl:, 1966a). The numbers of eggs deposited on
"Hudson" barley seedlings planted in plastic pots were counted and
three of these pots were held in each of nine growth chambers adjusted
to 48°, 58°, 67°, 76°, 80°, 85°, 90°, 95°, and 100° F. Relative
humidity and light period in all growth chambers were equally set at
75 percent and 16 hours respectively. The eggs were checked daily for
hatching and the numbers hatched and the number of days required for
the first and last eggs to hatch were recorded.

22

23

For the larvae, a plastic pot containing about 60 four-inch
tall "Hudson" barley seedlings was first caged with an ordinary lamp
chimney by simply placing it on the top of the pot above the soil
level. Thirty newly eclosed larvae were then transferred into each
cage through an opening at the top which was later covered with a fine
nylon cloth. Three pots of barley containing a total of 90 young
larvae were placed in each growth chamber. The number of days required
for the first and last larvae to go into pupation was recorded.

For the test of the pupal stage, thirty prepupae were placed
in each lamp chimney cage with some fresh plants. Three cages were
placed in each growth chamber and the days first and last prepupae
entered the soil for pupation and again the days first and last new
adults emerged from the soil were recorded. The number of the new
adults emerged as well as that of the eggs hatched were counted to
obtain percentage mortality.

The data were analyzed using Davidson's (1944) logistic formula
and linear regression equation for time-development relationship. Tb
estimate the thresholds for development of each stage, Uvarov's (1931)
equation and straight velocity line method (Matteson and Decker, 1965)
were used.

Results: A complete development from an egg to adult occurred
at 58° F. and as high as up at 90° F. The overall results of this
experiment are shown in Table 3.

At 48° F., neither eggs nor larvae completed their development.
A complete kill of the eggs and larvae at 48° F. was observed after
four and eleven weeks respectively. At 95° F., on the other hand, the

eggs hatched but larvae did not complete their development. The thermal

24
death point for the egg stage apparently lies between 95° and 100° F.
and that for the larval stage between 90° and 95° F. A 100 percent
mortality of the larvae was observed after eight weeks at 95° F. The
rate of development is highest at 90° F. in this test. Mbrtality of
all immature stages, however, is lowest at the intermediate temperatures
of 76° F. and 80° F. and it gradually increases as the temperature
deviates from this range.

TABLE 3.-—Duration of development and mortality of the cereal leaf
beetle at various constant temperatures

 

 

Z Mortality

 

Duration of Development in Days

 

 

Larva
Temp. °F. Egg Larva Pupa Total Egg and Pupa
48 No hatching No complete development 100 100
58 18i4 27i§ 47i5 92:14 74 64
67 11:2 161? 25:3 52:7 59 34
76 7.5:l.5 13.5:d.5 18i2 39i§ 28 40
8O 5.5:15 9.5:1.5 12.5:1.5 27-5i4-5 21 47
85 Si} 8.5:0.5 10.5i0.5 24:2 38 67
90 4.51} 81d lOid 22.5:2.5 40 59
95 4.5:1 No complete development 41 100

100 No hatching 100

 

The data shown in Table 3 are generally in agreement with those
reported by Knechtel and Manolache (1936) and Castro_g£”al. (1965)
in Table 2. Durations of pupal stage reported by the former, however,
are significantly shorter than those in Table 3. The differences were

apparently due to the difference in measurement of the duration of

25
pupal stage. The author measured the duration of pupal stage as the
period from the day prepupae enter the soil for pupation until the day
they emerge as adults. Knechtel and Manolache (1936) apparently
measured the true pupal period within the pupal cases.

Analyses of the Data: The reciprocal values of the days required

 

for egg, larval, and pupal stages to develop at different constant
temperatures denote the rate of development and form an S-shaped veloc-
ity curve when the values are properly plotted. Davidson's (1944)

equation of

was used to show the relationship between temperature and the time re-

quired for development in the cereal leaf beetle. A brief explanation

on this formula is already given in a section of literature review and

the details on computation of K, a, and b values are given by Davidson
1 . . . 100

(1944). When §-is multiplied by 100, the product —§—-represents

average percent development of a given stage per unit time. The values

 

of y and 100 for each corresponding temperature are shown in Table 4.
The graphic representations of the equations derived from
Davidson's formula (Davidson, 1944) for the development of egg, larval,

pupal, and entire immature stages are shown in Figures 2, 3, 4, and
5 respectively. The equations used for drawing the curves, along with

linear regression equations for the rate of development, are summarized

in Table 5.

26

TABLE 4.--Number of days required for a complete development (y) and

the speed of development in terms of percent development in one day

(lOO/y) of egg, larval, pupal, and entire immature stages of the
cereal leaf beetle at different constant temperatures

 

 

 

 

 

 

Temp. °F. Larva Pupa All Stages
192 .122 ya 22
X Y Y Y Y Y Y Y Y
58 18. 5.556 27.0 3.704 47.0 2.128 92.0 1.087
67 11. 9.091 16.0 6.250 25.0 4.000 52.0 1.923
76 7. 13.333 13.5 7.407 18.0 5.556 39.0 2.564
80 5. 18.182 9.5 10.526 12.5 8.000 27.5 3.636
85 5. 20.000 8.5 11.765 10.5 9.524 24.0 4.167
90 4. 22.222 8.0 12.500 10.0 10.000 22.5 4.444
95 4. 22.222
varience 37.405 9.970 15.661 1.476

 

227

35r

1*8 mus-mun:
0.2500

Y

A.\oo_c

2 5 O 01
l + elem-alum

.1911 -
y

  

>8 25 E «553.33 2.3:... 3222

/

  

A>L mxao

5

I5
'I l0
5

IO’
5

5

uo__om =o_.~n=u=_

9O

80

7O

60

50

 

Temperature, F.

Fig. 2 - Temperature-time (closed circles) and temperature-velocity (open circle) curves for

the egg stage.

28

2x8: to 25 5 233.38 .58: 3222

 

 

l3.33l2

'+ e VOOIV'AHOIX

 

32.
Y
/
O

O O

I +e7..017-O~H§!X

 

  

IO-"|'--"-"|'|'-'T'I"""""|'"O'l""'--‘O'I'O'--"l-"-""'l---l

90

50

80

7O

60

Temperature, F.

 

7O
60

w 4 w.»

A: :3 E 32» .23.. 3 .3223

 

Fig. 3 - Temperature-time (closed circles) and temperature-velocity (open circles) curves for

the larval stage.

29

 

23:: 3o 25 E 225933 2.33.. out»:

 

 

 

 

w m 5
‘I ‘ ‘t it I‘ d
llllllllllllllllllllllllllllllllllllllllll A
x o
u u
M O O. 1%
3a
9...
6N
'5. o . A
0”
l».
+
l O
O A
. me
0
0V. ee
. F.
e:
w
x o t.
u 47. m
u / w
a? o o m
.l T
4.0 I
"'
JO
8 LO
+ 6
l o
.w

I20 '
IOO '
8
6
4

t: :8 5 82m .32 .0 522.5

 

Fig. 4 - Temperature-time (closed circles) and temperature-velocity (open circles) curves for

the pupal stage.

30

23°: >3 25 5 23.5233 233.. 3222

6 4. 2

1 1‘ 4 ‘ 1

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
l

4 6757
He 0 ens-anus
/.....cu0
\.

  

 

IOO
Y

0.010.! ~e.rcux

I+e
00468

 

y.

I20r
BOI

m m m

A: 18 5 3:5 223:... .23 .o 322.5

I40 '
IOO '

 

90

80

7O

6O

50

Temperature, F.

Fig. 5 - Temperature-time (closed circles) and temperature-velocity (open circles) curves for

the entire immature stage.

31

 

m
» xmwNH.o i momm.w + H m

 

 

 

 

 

 

“meoeo.o
eqmm.o «mme.m - xmoHH.o u . u u a Hmuoa
m+
ooH Hmeo s 00H xmmNH.o . monm.m H
m xmmoH.o - eHem.HHm + H a mmoHoH.o
mmwm.o wemq.mH u me©N.o u ooH mmoH.oH u 00H m + H u a «mum
xmmoH.o . «Hum.HH
» xquH.o - HmHm.Hm + H a NHmmmH.o
Nmmm.o cowo.mH . xoowm.o u ooH NHmm.mH u 00H m + H u » m>umH
quHH.o . mNHm.n
% xmqu.o . oomq.em + H % mHoomN.o
comm.o «om.om - xmnem.o u ooH mHoo.mN u ooH m + H u a wwm
xeeoH.o . coae.n
ucmwoauwmoo mumm mnu How mumm coHumusa mwmum
:oHumHmuuou coHumsvm conmmuwmm
mafia uzwwmuum m>uso oflumfiwoq

 

 

maummn mama Hmmnmo
mzu mo mmwmum ucmummwww mo ucmEQon>mw mnu How mcofiumavw mafia uswfimuum cam m>u=u oHumfiwoqii.m mqm<a

In Figure 2, the observed points lie very closely along calcu-

32

lated curve lines except points at 58° and 760 F.

Apparently the

temperatures in these particular growth chambers were not adjusted

properly.

58° or 760 F. because the same trend is observed in Figures 3, 4, and

The actual temperatures could have been somewhat lower than

5 and in Table 6 which shows the deviation between observed and cal-

culated 100

 

values.

other temperatures.

The deviation is largest at 76° F.

TABLE 6.--A comparison of observed and calculated

 

than at any

0 values

 

 

 

 

 

 

 

 

 

Egg Stage Larval Stage
Temp. °F. Obs. Calc. Obs.-Ca1c. Obs. Ca1c. Obs.-Ca1c.
58 5.556 4.867 +0.689 3.704 3.110 +0.594
67 9.091 9.557 -O.466 6.250 6.133 +0.117
76 13.333 15.327 -1.994 7.407 9.395 -1.988
80 18.182 17.672 +0.510 10.526 10.521 +0.005
85 20.000 20.056 —0.056 11.765 11.582 +0.183
90 22.222 21.833 +0.389 12.500 12.292 +0.208
Pupal Stage Entire Immature Stage
Temp. °F. Obs. Calc. Obs.-Ca1c. Obs. Calc. Obs.-Ca1c.
58 2.128 1.358 +0.770 1.087 0.853 +0.234
67 4.000 4.106 -0.106 1.923 1.944 -0.021
76 5.556 7.601 -2.045 2.564 3.246 -0.682
80 8.000 8.651 -O.651 3.636 3.706 -0.069
85 9.524 9.440 +0.084 4.167 4.108 +0.059
90 10.000 9.835 +0.165 4.444 4.359 +0.086

 

33

At 95° F., the rate of development of the egg remains same as
that observed at 900 F. although the curve values are constantly in-
creasing. This would indicate that there is a break point between
90° F. and 950 F. Davidson (1942) described this break point as the
peak temperature at which the embryo develops at the fastest rate.
The peak temperature for the cereal leaf beetle egg is 92.50 F. As
Figure 2 shows, the velocity curve is straight between 650 F. and 800 F.
and this temperature range corresponds to an optimum range for the
development of the cereal leaf beetle.

The rate of development in larval stage (Figure 3) is consider-
ably lower than that in egg stage, still lower in pupal stage
(Figure 4), and the lowest when entire immature stages are lumped to—
gether (Figure 5). Obviously this is because the incubation period
is the shortest compared to any other stages. In general, the curves
follow closely along the observed points in every stage except points
at 58° and 760 F.

It was mentioned earlier that the rate-of—development or veloc-
ity curve is S-shaped. In medium range of temperatures, however, the
curve is very straight. Assuming a linear relationship between tem-
perature’and the rate of development, a linear regression equation was
computed for each stage (Figure 6 and Table 5).

As Figure 6 shows, all the observed points fall surprisingly
close to the calculated equation lines. A further checking of the
values revealed that an accurate estimation on the duration of develop-
ment of a given stage could be made with these straight lines within a
temperature range of 550 F. to 90° F. Below 55° F. and above 900 F.,

Davidson's curve lines gave more accurate estimations.

AVERAGE PERCENT DEVELOPMENT IN ONE DAY (loo/7)

28*

20.

34

 

l A/ L ‘ l I L L A A

 

 

50 60 7O 80 90

Temperature, F.

Fig. 6 - The rate of development of egg, larval, pupal, and entire immature stage at different
constant temperatures.

35
A method for estimating threshold of development is to locate
the point at which the velocity line crosses the temperature scale.
The temperature at this crossing point is an estimation of the thresh-

old (Matteson and Decker, 1965). Another method is to use Uvarov's

dt - DT

(1931) formula, K = d _ D .

Using 67° F. for t and 850 F. for T the
threshold of development for each stage was calculated. The thresholds
of development of the cereal leaf beetle, using both methods, are
given in Table 7.

TABLE 7.-—Ca1culated thresholds for development of the cereal leaf
beetle.using two different methods

 

 

 

Stage Uvarov's Equation Velocity Line
Egg 52.00 F. 49.10 F.
Larva 46.6 45.7

Pupa 54.0 51.1

All stages 51.6 49.2

 

Table 7 indicates that the larval stage has the lowest thresh-
old, the egg stage intermediate, and the pupal stage the highest
threshold value for development. The threshold values obtained from
Uvarov's equation, however, seems to be more closer to the actual
values in the cereal leaf beetle. Knechtel and Manolache (1936) re-
ported the thresholds for the development of the cereal leaf beetle as
53.6° F. for the egg and larva and 48.2° F. for the pupa. The thresh-
old for the egg and larva seem to be somewhat higher while that for
the pupa is considerably lower than the calculated thresholds obtained

from this study.

36
Experiment 2. Egg Production and Development of Pupae at 80° F.
and 85° F.

Methods: It was learned from previous experiment that the
cereal leaf beetle is capable of developing from an egg to adult within
a temperature range of 52° F. to 92.50 F. It was, however, desirable
to determine an optimum temperature level at which the largest number
of the beetle could be reproduced within a relatively short period of
time. Two temperatures, 800 F. and 85° F., were selected to conduct
this study.

In the first test, 30 adults that had been stored for 50 days
at 380 F. were placed in each lamp chimney cage containing "Clintland
60" oat seedlings. Three cages with a total of 90 adults were held in
each of two growth chambers adjusted to 800 F. and 850 F. In both
chambers relative humidity and light period were set at 75 percent and
16 hours respectively. The plants were changed every other day and
the number of eggs deposited was counted. The egg counts were made
until the last female laid the last eggs.

In Test 2, the methods employed were exactly the same as in
Test 1 except that the adults used in the second test had been stored
at 38° F. for 90, 155, and 250 days prior to the test. Thirty adults
were randomly selected from each group and they were placed separately
in each lamp chimney cage. This set of three cages were then held at
800 F. and 850 F.

Until Dr. W. C. Myser of Ohio State University developed a
method of sexing the adult beetles in 1966, the sexing was done by

either 1) picking up mating pairs before they start laying eggs or

37

2) picking up a given number of pairs by their general appearance.
All the beetles were dissected for sexing after they died and the
number of eggs laid per replication was calculated by equating the
number of females present to a predetermined number.

Survival of the pupae at 800 F. and 850 F. was also investigated.
Three petri dishes, each containing 30 pupae, were placed in each
growth chamber and the number of adults emerged was counted. The data
were analyzed using an F-test.

Results: Table 8 shows a greater egg production at 80° F.
than at 850 F. The difference, however, is not significant according
to an F-test.

TABLE 8.--Egg production at 80° F. and 85° F. by the adults that had
been stored for 50 days at 38° F.-—Test 1

 

 

Total number eggs laid
per cage per 15 females

 

 

Temp. °F. I II III Total Mean Std. dev.
80 564 2,235 1,273 4,242 1,412 686.96
85 624 210 675 1,509 503 208.23

 

F = 2.2590 (N. Significant)

A considerable variation in the number of eggs among three
replicated cages exists and the high standard deviation values in-
dicate the magnitude of variation. Such variation was frequently
observed among the beetles that were not completely out of diapause.
It can also be attributed to the individual difference existing among

the beetles.

38
The data obtained in the second test were analyzed using a
Chi—square method (Table 9). The number of eggs produced by three
different groups of adults at 800 F. is significantly greater than
that at 850 F. From these tests it appears that 80° F. seems to be
more favorable for egg production in this beetle.

TABLE 9.--Egg production at 800 F. and 850 F. by the adults that had
been stored at 38° F. for 90, 155, and 250 days--Test 2

 

 

Total Number Eggs Laid
per Cage per 15 Females

 

 

 

 

Temp. oF. Freq. 90 155 250 Chi2
80 Obs. 1,005 724 452
Exp. 1,038.5 693.8 448.7
Chi2 1.081 1.315 0.024 2.420
85 Obs. 652 383 264
Exp. 618.5 413.2 267.3
Chiz 1.815 2.207 0.041 4.063
2

Chi = 6.483 (Signif.)

The development of pupae was also tested at 800 F. and 850 F.
The difference in the number of adults emerged at 800 F. and 85° F. is
not statistically significant. The results of this test is shown in

Table 10.

39

TABLE 10.--Development of pupae at 800 F. and 850 F.

 

 

No. New Adults Emerged
per 30 Pupae

 

 

Percent
Temp. oF. I II III Total Mean Emergence
80 14 13 21 48 16 53.3
85 9 18 18 45 15 50.0

 

F = 0.1071 (N. Significant)

Experiment 3. Development of Larvae and Pupae at 730 F. and 800 F. on
Oats and Barley

 

 

Methods: General rearing procedures for the larvae have al-
ready been described in Experiment 1. TWenty first-instar larvae were
transferred into each lamp chimney cage containing about 50 seedlings
of "Clintland 60" oats or "Hudson” barley. Five cages each of oats
and barley were held in each of two growth chambers set at 73° F. and
80° F., 75 percent relative humidity, and 16 hours light period. The
young larvae were allowed to develop inside the cage until they reached
the adult stage and the number of adults emerged was counted. The
data were analyzed using a Chi-square method.

Results: The experimental results are shown in Table 11.

The association between food plants and temperatures, that is
the development and emergence of the beetle under any particular com-
bination of temperature and food plant, is not significant according
to a 2 x 2 Chi-square test shown in the table. Individual test, how-
ever, indicated that at 73° F. the number of adults emerged from barley
was significantly higher than that from oats when a "t" test was used.

It was observed in the laboratory that barley is generally more

4O
tolerant than oats against feeding damage done by larvae and adults.
The amount of food, 50 plants per 20 larvae per cage, was supposed to
be enough for the larvae to complete their development.

TABLE ll.--Number of adults obtained from larvae reared on oats and
barley at 73° F. and 800 F.

 

 

 

 

 

 

 

Oats Barley Total
,2 2 ,2
Temp. OF. Obs. Exp. Chi Obs. Exp. Chi Obs. Chi
73 33 39.23 0.989 69 62.77 0.618 102 1.607
80 42 35.77 1.085 51 57.23 0.678 93 1.763
Total 75 120 195 3.370
(N. Signif.)

The difference in adult emergence on oats and barley may be due
to the following reasons. 1) The larval development was better on
barley at 73° F. 2) Oat seedlings break easily from a little injury
or weight and this might have caused an excessive larval movement
within a cage and consequently caused a higher mortality of larvae
and pupae.

Experiment 4. Egg Production under Fluctuating and Constant
Temperatures

 

 

 

Methods: Adult beetles that had been stored for 110 days at
38° F. were used for this experiment. Ten pairs of adults were placed
in each lamp chimney cage with "Clintland 60" oat seedlings. Three
cages were held in the first growth chamber that was initially adjusted
to 700 F. for the day and 50° F. for the night. The initial tempera-

tures of 700 - 50° F. were selected because they approximate the mean

41
day and night temperatures under field conditions in mid-May near
Galien, Michigan. Two other cages with 20 adults in each were held in
the second growth chamber that was set at a constant 800 F. Relative
humidity and light period in both growth chambers were set equally at
75 percent and 16 hours respectively. The plants were changed every
other day for egg counts.

Since egg production was extremely poor under fluctuating
temperatures, the temperature in the first growth chamber was even-
tually raised to 800 F. constant after 36 days at 700 — 500 F. and
again after 25 more days at 750 - 650 F.

Results: It is apparent from Table 12 that fluctuating day and
night temperatures are not favorable for the female beetles to lay
eggs consistently.

In the growth chamber with fluctuating temperatures, the adult
beetles laid very few eggs. When temperature was raised to constant
800 F., the beetles laid as many eggs as those produced by the beetles
that had been held at 800 F. from the beginning of the test. Under
low fluctuating temperatures egg laying was extremely poor but the
beetles survived for much longer period than those at constant 800 F.
After the beetles were exposed to a constant 800 F., their total egg
production nearly equalled that of the adults which had been maintained
at 80° F.

During an initial 36-day period, the beetles laid a significantly
greater number of eggs at constant 800 F. than at 700 - 500 F. The
difference in mean egg production under these two different conditions
was highly significant according to a "t" test. The difference in mean

total egg production during entire testing period at constant 800 F.

42
and under fluctuating temperatures, however, was statistically not
significant.

TABLE 12.--Egg production by overwintered adults under constant 80° F.
and fluctuating day and night temperatures

 

 

No. Eggs Laid per
Cage per 10 Females

 

 

 

 

 

 

Temp. °F.: Duration
Initial Temp. Day-Nighta in Days I II III Total Mean
70 - 50 Initial 36 111 28 35 174 58
FIUCtuating 75 - 65 Second 25 167 0 0 167 56

Temp.
80 Const. Last 154 557 1,135 1,804 3,496 1,165
Total 215b 835 1,163 1,839 3,837 1,279
80 Initial 36 1,126 1,057 --- 2,183 1,092
Constant

80° F. 80 Second 25 127 411 —-- 538 269
80 Last 49 90 0 --— 90 45
Total 110b 1,343 1,468 --- 2,811 1,405

 

a16-hour light and 8-hour dark periods.

bAlso LB.

99 for the adults.

It is believed from this experiment that under normal field con-
ditions the spring adults could survive for a considerable period of
time in cold spring of Michigan and lay most of their eggs when weather,
especially temperature, becomes favorable. Later observations indicated
that the beetles lay eggs at constant temperature of 60° F. and fairly
consistent number of eggs when temperature reaches a constant 70° F.

The mean temperature of 75° - 65° F. is 70° F., and yet the egg laying at

these fluctuating temperatures is poor and erratic. The slowing effect

43
of low night temperature on sexual activity seems to be much greater

than was anticipated.

Experiment 5. Mortality of Different Stages of the Beetle at
Extremely High and Low Temperatures

 

 

 

Methods: Numerous preliminary trials were made using a small
number of insects to obtain a lethal temperature range. After this
range was obtained, eggs, larvae, pupae, and adults were exposed
directly from room temperature to various extreme temperatures for
different lengths of time. A minimum of two replications of 60 in-
dividuals was used for determining each percentage mortality value.
Mortality of a given stage at room temperature was used as a check in
computation of Abbott (1925) Percentage mortality. Freezers for low
temperatures and modified incubators for high temperatures were used
in this study. Relative humidity in these cabinets ranged from 60 to
80 percent and no light was provided.

Results: Table 13 shows percent mortality of eggs, larvae,
pupae, and spring and summer adults at various extreme temperatures.
The eggs are the most resistant stage against cold temperatures and 100
percent mortality occurred within 2 hours at -100 F. and in 4 hours at
0° F. The egg stage is then followed by pupae, larvae, active summer
adults, and lastly by active spring adults. Unfortunately overwintering
adults have not been tested and it is quite possible that these hiber-
nating adults might be the most resistant of all stages against the
cold. Castro e£_al, (1965) reported that 100 percent mortality of the.
diapausing adults occurred after 25 days at 0° F.

At higher temperatures of 1100 F. and 1200 F., inactive summer

adults were most resistant, and followed by larvae, egg, pupae and

44

 

 

 

 

om on 0m 0 953 m H
ooH Ha mm wwm
ooH me 6N mane
ooH mm He HH m>umq
ooH om mm nu am we UHso< .aam
o>fiuo<

ooH ow uHsb< .umm o
ooH me n wwm
ooH om mm 0 mean
OOH mm ma m>umq
ooH om nu 58 mm o uHsv< .asm
m>wuo<

ooH an oH ane< .anm oH-
w e N .6; H we oe om om mH oH m e m e N .cHa H ammum .mo .nana

 

muamomxm mo cofiumusa

 

 

mousumuanou oEonuxm msofium> um uasva mam .masd .m>umH .wwm mo hufiamuuoa ucoouomii.MH mqm<a

 

00H om mm ufiau< .adm

 

45

 

m>HuomcH
oo~ mm am 0 m>umq
OOH on o mwm
ooH an em ma 0 6H56< .aam
o>Huo<
ooH mm om mane
ooH mm om m UH=6< .unm oNH
ooH mm o 6H8e< .asm
m>wuomcH
ooH mH o wwm
ooH cc 0 n>unH
00H 04 NH 6H66< .unm
ooH mm o maam
ooH mm o 6H=6< .aam
6>Hun< oHH
m man 4 6 m e m N .4; H on oe om om mH oH .cHa m amnom .mo .asne

 

anamoqu mo cofiumuam

 

 

.e.ucoo--.mH mHm<a.

46
active summer adults, and spring adults. In the larval stage 100 per-
cent mortality occurred in 4 days at 110° F. and 3 days at 1200 F. A
complete kill of inactive summer adults was observed within 6 hours at
1200 F. and in 5 days at 1100 F. Mr. John T. Hayward of Plant Pest
Control Division, A.R.S., USDA reported that inactive adults can be
killed by a 20-minute exposure to 120° F. which is considerably shorter
than the author's observation of 6 hours at the same temperature

(personal communication with Mr. Hayward).

Experiment 6. Effect of Different Photoperiods on Egg Production

 

 

Methods: Two separate tests were conducted in the laboratory
to determine an optimum light period for oviposition by field-collected
summer adults that had been stored at 380 F. in the laboratory. In
the first test six growth chambers were adjusted to give 0, 8, 12, 16,
20, and 24 hours of light. Temperature and relative humidity were set
equally at 80° F. and 75 percent respectively in all the chambers.
Fifteen pairs of adults which had been stored 50 days at 38° F. were
placed in each lamp chimney cage with "Clintland 60" oat seedlings.
Three replicated cages were placed in each growth chamber and the
plants were changed every other day for egg counts.

It was learned from the first test that the egg production was
highest around a l6-hour light period. For the purpose of refining
the results obtained in the first test, l4-, l6-, and l8-hour light
periods were used in the second test. Ten pairs of adults that had
been stored at 38° F. for 77 days were placed in each lamp chimney
cage. The plants were changed once every four days and the number of

eggs deposited on the seedlings in each pot was counted. The test

47
was terminated after 63 days when no further egg production was ob-
served. The data were analyzed using an F—test.
Results: The results of the first test are shown in Table 14.
Egg production was highest under a l6-hour light period.

TABLE l4.--Egg production under different photoperiods during a 56-day
test period—-Test 1*

 

 

No. Eggs Laid per Cage
per 15 Females

 

Photoperiod in Hrs.

 

 

per 24-hr. Cycle I II 111 Total Mean
0 ll 12 5 28 9
8 0 2 4 6 2
12 O 34 l 35 12
16 881 1,101 968 2,950 983
20 1,040 502 413 1,955 652
24 174 0 O 174 58
F = 23.3875 (H. Significant) LSD 01 = 394
LSD 05 = 277

*Adults had been stored at 38° F. for 50 days prior to the test.

The differences between the number of eggs produced under 16 or
20 hours photoperiod and that under 0, 8, 12, or 24 hours light period
were highly significant according to an F-test. The egg production
under a l6-hour light period was again significantly greater than that
under 20 hours of photoperiod. At least in this experiment, a l6-hour
light period seems to be the most favorable region for the maximum
egg production in overwintered adults. Castro,_g£_al. (1965) have

already indicated that the beetles responded more readily and produced

48
more eggs'under 16 hours than under 12 hours of photoperiod and this
test confirms their results.

In the preceding test, a l6-hour photoperiod has been shown to
be a close estimate of the optimum light period for the spring adults.
In order to obtain more detailed information regarding the optimum
photoperiod, 14, 16 and 18 hours of light periods were selected in the
second test. The results are shown in Table 15 and Figure 7.

TABLE 15.-—Egg production under l4, l6, and 18 hours of photoperiods
during a 63-day test period——Test 2*

 

 

NO. Eggs Laid per Cage
per 10 Females

 

Photoperiod in Hrs.

 

per 24-Hr. Cycle I II III Total Mean
14 65 581 347 993 331
16 1,339 936 496 2,771 924
18 1,397 441 932 2,770 923

 

F = 1.8811 (N. Significant)

*Adults had been stored at 38° F. for 77 days prior to the test.

The beetles held under either 16 or 18 hours of light produced
nearly three times as many eggs as those laid under a l4-hour light
period. The number of eggs laid under three different light periods,
however, was not significantly different from one another according to
an F-test. As Figure 7 indicates the rate of oviposition was higher
under 18 hours than under 16 hours of photoperiod during an initial 32—
day period. This seems to indicate that a l8-hour photoperiod could
be the more accurate estimation of the true optimum photoperiod for

the spring adults.

EGGS PER CAGE

N0.

MEAN

I,OOO

800

600 "

400

200

I

 

49

1Entire 63‘doy period

 

\\ Presumed direction of
\ the curve

 

l4 l6 l8 20

Photoperiod (Hrs.)

Fig. 7 — Mean total number of eggs laid per 15 females under l4, 16, and l8 hours

of light periods.

50

Experiment 7. Development of Immature Stages under Different
Photoperiods

 

 

 

Methods: TWO pots of "Clintland 60" oat seedlings with known
number of eggs were held in each growth chamber adjusted to 0, 8, 12,
16, 20, and 24 hours photoperiods, 80° F., and 65 percent relative
humidity. The number of eggs hatched was later counted and percent
egg-hatching was calculated.

Forty newly eclosed larvae were randomly selected from the above
egg samples and were divided equally into two lamp chimney cages con-
taining fresh "Clintland 60” oat seedlings. These two cages were held
in the same growth chamber from which the larvae were taken. The
number of adults emerged in each cage was later counted and it was con-
verted to percent adult emergence.

Results: As Table 16 indicates the development of the egg stage
is not directly influenced by different light periods. It is rather
influenced by temperature. The egg hatching ranged from 71 percent
under an 8-hour light period and 82 percent under complete darkness.
The larval development, however, varied considerably. There were no
apparent differences in larval and pupal growth when the light period
was 16 hours or more. The adult emergence was fair under a 12-hour
photoperiod, poor under 8 hours of light, and no adults emerged under
complete darkness. The poor adult emergence under 0 and 8—hour photo—
periods was not due to a direct effect of the short light periods on
the insect growth but it is rather due to a poor plant growth under
the 0 and 8-hour photoperiods. Under a 24-hour light period, the larval

and pupal development seems to be slightly hastened.

51

 

 

m.am o.o¢ o¢\oH 5.8m omH\NeH em
o.¢m o.o¢ oq\oH m.Ho Hoa\mm om
m.mm m.m¢ oq\uH w.mm omH\mNH 0H
o.mm o.mm oq\¢H o.mm moH\mHH NH
m.¢H 0.0m oq\w H.Hm mmH\oa w

o o o «.mw mmH\HHH o

wwm ecu Eouw wocmwuoem ucommum om>umq wcfinoumm mammmum wwwm .oz ooHquODOSm
oompoEm quo< ucoouom maso< ucoouom \wowuoem moadp< .oz ucmonom \omnoumm wwwm .oz

 

 

mooHHoQODOLQ unonHMHo woman woman mam .mm>HmH .mwwm mo ucoEmon>ini.oH mqm<H

52

Experiment 8. Egg Production during Day and Night Hours

 

 

Methods: Twenty—five adults that had been stored at 38° F. for
104 days were placed in each of three lamp chimney cages containing
"Clintland 60" oat seedlings. All of the cages were held at 80° F.,
75 percent relative humidity, and 16 hours photoperiod. The plants
were changed twice a day, once at the end of a l6-hour light period
and again at the end of an 8-hour dark period, and the number of eggs
deposited on the plants was counted. The data were analyzed using a
t-test.

Results: Table 17 shows that the majority of the eggs (93.1%)
were laid during a 16-hour light period and only 6.9 percent of the
eggs were deposited during the 8 hours of dark period.

TABLE l7.--Number of eggs laid during day and night hours for a 10-day
period on oats

 

 

 

 

Repl. (day) Day (16 hr.) Night (8 hr.) Total

1 178 18 196

2 248 18 266

3 266 25 291

4 265 14 279

5 263 22 285

6 252 15 267

7 233 10 243

8 218 19 237

9 209 14 223

10 175 16 191

Total 2,307 171 2,478
Z Eggs 93.1 6.9

 

t = 3.1255 (Significant)

53
A ”t" test showed that the number of eggs laid during day hours
is significantly greater than that deposited during night hours. The
oviposition activity in this insect, therefore, is strongly affected
by the presence or absence of light and most of the eggs are laid
during day time.

Experiment 9. Effect of Different Relative Humidities on Egg
Production

 

 

 

Methods: Sixty adult beetles that had been stored for 123
days at 38° F. were placed in each plastic screen cage (9-1/2 x 9-1/2 x
12 inches) with two pots of ”Clintland 60" oat seedlings. Two cages
were held in each of three growth chambers that were set at 45-55
percent, 70—80 percent, and 95-100 percent relative humidity. Tempera-
ture and light period in all three chambers were equally adjusted to
800 F. and 16 hours respectively. The plants were changed once every
four days and the number of eggs laid was counted during the 62-day
test period. The data were analyzed using an "F" test.

Results: An F—test shows that the number of eggs laid by the
adults that had been exposed to different relative humidities is
significantly different from each other. The least significant dif-
ference (LSD) of 175 in Table 18 indicates that the beetles that had
been exposed to 95-100 percent relative humidity laid significantly
greater number of eggs than the beetles that had been treated at the
other relative humidities.

It was observed during the test period that some beetles re-
mained quite inactive especially among the beetles that had been ex-
posed to 45-55 percent relative humidity. Along with other environ-

mental factors such as temperature and photoperiod, relative humidity

54
seems to be an important factor affecting the reproductive activity

and egg production in the spring adults.

TABLE 18.-—Egg production under different relative humidities*

 

 

No. Eggs Laid per Cage
per 30 Females

 

Percent Relative

 

 

Humidity I II Total Mean
45-55 0 0 0 0
70-80 88 258 346 173
95-100 972 926 1,898 949
F = 78.9322 (Significant) LSD 05 = 175

*Adults had been stored at 38° F. for 123 days prior to the test.

Experiment 10. Effect of Different Soil Moistures on Development of
Pupae and Emergence of Adults

 

 

 

Methods: This study consists of three separate tests. In
Test 1, twenty third-instar larvae were placed in each lamp chimney
cage containing "Clintland 60” oat seedlings. The larvae were allowed
to feed and pupate in the same cage. All the cages were held at
80° F. and 12 hours light period. The soil moisture was roughly ad-
justed in four different ways as follows.
1) Dry: No water was added to the soil after all the larvae
entered the soil for pupation.
2) Moist: Caged plastic pots were placed in a water tub after
all the larvae entered the soil. The water level in
the tube was maintained up to the same level of the

soil surface in the pot.

55

3) Wet: Caged pots were placed in the water tub from the

beginning of the test.

4) Normal: The soil was watered once every three days with a

watering can.

In Test 2, fifty grams of oven—dry white silica sand was poured
into each 9—ounce glass jar. The sand was then mixed with a proper
amount of water to give a desired percentage moisture by dry weight
basis. The white sand was used simply because of its ease of handling.
The moisture contents of the sand were maintained in three different
levels, 0, 12.5, and 25 percent. Thirty pupae in their pupal cases
were placed on the sand surface in each jar.

In Test 3, twenty pupae were suspended in the air above the
sand surface by means of a piece of copper screen in each jar. Five
different moisture contents, 0, 12.5, 25.0, 37.5, and 50 percent were
used in this test. Both Tests 2 and 3 were conducted at 85° F. and
16 hours light period. In all three tests the number of adults
emerged in each cage or jar was counted and the results were analyzed
using an F-test.

Results: As shown in the third treatment (wet) of Table 19,
all the mature larvae were unable to pupate in the flooded soil and
consequently there was no adult emergence. The larvae in these
flooded pots were found dead from the excess water in the soil.

When the soil was flooded after all the larvae entered the soil
(moist), the pupation apparently took place without any appreciable
mortality of the pupae. An F-test, however, indicates no significant
difference in the number of adults emerged from cages with different

soil moistures. Sample size used in this test seems to be too small

56
to detect any significant differences in the number of adults emerged
from different cages. However, the results of this test generally in-
dicate that an excess water in the flooded soil is detrimental for the
prepupae entering the soil for pupation. Dry and moist soil or the
soil flooded after the pupal case is formed do not seem to affect the
pupation process.
TABLE 19.--Development of pupae and emergence of adults from larvae

that were allowed to pupate in the soil with different moisture
contents--Test l

 

 

No. Adults Emerged
per 20 Larvae

 

 

Percent
Soil Moisture I II III Total Mean Emergence
Soil 7 13 2 22 7.3 29.3
Moist 7 7 7 21 7.0 28.0
Wet 0 0 0 0 0 0
Normal 8 4 5 17 5.7 22.7

 

F = 3.7835 (N. Significant)

The results of Test 2 shown in Table 20 are generally similar
to that of the previous test.

When the data were analyzed using an F-test, the differences in
the number of adults emerged from different jars were highly significant.
The less the moisture content of soil, the higher was the percentage
of adult emergence. There was a 100 percent mortality of the pupae in
jars with 25 percent moisture. An appreciable amount of free water
existed on the sand surface in these jars and this excess water was be—

lieved to be the cause for the complete kill of the pupae. The pupae

57
used in this test were collected from the cereal leaf beetle rearing
room and many pupal cases were apparently damaged during the collection
process. The excess water on the sand surface then penetrated into
the pupal case causing suffocation and death of the pupae.

TABLE 20.--Emergence of adults from pupae that were placed on white
sand with different moisture contents--Test 2

 

 

No. Adults Emerged
per 30 Pupae

 

 

 

Percent Percent
Soil Moisture I II III Total Mean Emergence
0 22 24 19 65 21.7 72.2
12.5 7 4 11 22 7.3 24.4
25.0 0 0 0 0 0 0
F = 39.7457 (H. Significant) LSD 05 = 6.9

As Table 21 indicates the higher relative humidity resulting
from higher soil moisture content seems to favor the pupal development.
The differences in the adult emergence from differently treated jars,
however, are not significant according to an F-test.

The wet soil seems to be detrimental for the larvae entering
the soil for pupation. Flooding of the soil during peak prepupal
period, if it is feasible, may be effective for control of the summer
adult population. Knechtel and Manolache (1936) reported that spring
rain in May and JUne caused a heavy mortality to the larvae in Europe

and this experiment partially acknowledges their report.

58

TABLE 21.--Emergence of adults from pupae that were suspended above
white sand with different moisture contents--Test 3

 

 

No. Adults Emerged
per 20 Pupae

 

 

Percent Percent
Soil Moisture I II III Total Mean Emergence
50.0 16 18 19 53 17.7 88.3
37.5 14 20 18 52 17.3 86.7
25.0 15 15 6 36 12.0 60.0
12.5 16 17 10 43 14.3 71.7
.0 16 8 8 32 10.7 53.3

 

F = 1.9059 (N. Significant)

Experiment 11. Effect of Different Soil Types on Oviposition

 

 

Methods: A wooden flat, 20 x 14 x 3 inches, was about two-
thirds filled with regular potting soil and was visually divided into
four equal sections. In the middle of each section a row of 15
"Clintland 60" oat seedlings were allowed to grow until they reached
about 5 inches tall. The top one-third portions of the four sections
were then filled with 1) white silica sand, 2) muck, 3) potting soil,
and 4) fine sand.

Thirty adults (15 pairs) that had been stored for 128 days at
380 F. were placed in the flat and they were covered with a wooden
frame screen cage with a plexiglas top (20 x 14 x 14 inches). The
plants were changed daily for six consecutive days and the number of
eggs deposited was counted. The data were analyzed using an "F" test.

Results: The results of this experiment are summarized in

Table 22. The number of eggs deposited on oat seedlings planted in

59
four contrasting soil types is not significantly different from one

another according to an F-test.

TABLE 22.--Oviposition of eggs on oat seedlings planted in different
types of soil

 

 

No. Eggs Laid per Day

 

Percent Eggs

 

Soil Type I II III IV V VI Total Mean Deposited
White Sand 24 14 25 23 27 35 148 24.7 27.8
Muck 16 25 34 17 25 24 141 23.5 26.4
Potting Soil 16 27 16 22 21 34 136 22.7 25.5
Sand l4 l4 9 23 26 22 108 18.0 20.3

 

F = 3.2874 (N. Significant)

The soil type, especially color, apparently does not exert any
influence on oviposition behavior of the cereal leaf beetle as long as
preferred host plants are available to the beetle.

Experiment 12. Effect of Different Soil Types on Pupation and
Emergence of Adults

 

 

 

Methods: Three contrasting soil types, muck, fine sand, and
regular potting soil in plastic pots were used for this test. For the
muck and fine sand, the bottom half of the pots were first filled with
regular potting soil and the upper half with muck or fine sand.
"Clintland 60" oat seedlings were grown in these pots and 25 third-
instar larvae were placed in each pot before they were caged with a
lamp chimney. All the pots with the larvae were held at 78° F., 65
percent relative humidity, and 16 hours photoperiod. The larvae were

allowed to feed and pupate in the same cage and the number of adults

60
emerged in each cage was counted. The results were analyzed using an
F-test.

Results: The number of new adults emerged in each pot is shown
in Table 23. The adult emergence was generally poor in all three soil
types. Although the difference in the number of adults emerged among
three different soil types was statistically not significant, a loose
muck soil seems to be more favorable for pupation than the other two
soil types. From the regular potting soil, which contained the largest
amount of clay, only 8 adults emerged.

TABLE 23.-—Development of pupae and emergence of adults from larvae in
different types of soil

 

 

No. Adults Emerged
per 25 Larvae

 

 

Percent
Soil Type I II III IV Total Mean Emergence
Muck 4 4 6 19 33 8.3 33.0
Sand 0 0 8 6 14 3.5 14.0
Potting Soil 2 1 3 2 8 2.0 8.0

 

F = 1.667 (N. Significant)

From the author's own experience, the ideal soil type for pupa—
tion of the cereal leaf beetle seems to be the one which is a rela—
tively light and well aerated soil. A soil which contains a large
amount of clay has a high water adsorbing capacity during the rainy
season and would become hardened during the drought season. This type
of soil would obviously drown and suffocate the beetle when it is wet

and would block the way out for newly formed adults when dry.

61

In Galien, Michigan where the heaviest infestation occurs, the
soil is generally heavy yet the beetle population remains at high level.
The primary reason would be probably due to a relatively dry weather
in the area during pupation period. In the case of dry heavy soil, the
prepupae enter the soil following the stem of host plant or through
cracks or any openings on the soil surface. As long as weather remains
relatively dry the cracks would remain opened and the new adults would
emerge without any difficulty through the same route they chose when
entering the soil as prepupae. The amount of precipitation during the
peak pupation period would undoubtedly alter the physical property of
the soil and this in turn seems to influence the abundance of beetle
population.

The soil type and soil moisture also influence the soil tempera—
ture. A heavy wet soil would absorb the solar heat more readily than
a light dry soil. It was demonstrated in an earlier test that the
cereal leaf beetle pupae could not develop at 95° F. and above in the
laboratory. In the field, however, the soil temperature can reach
128° F. at the surface (Ruppel gpual. 1965), and yet the pupae somehow
managed to survive and the new adults emerge. The temperature is
usually highest at the soil surface but it seems to drop considerably
l to 2 inches below the soil surface where the beetles pupate.

The author believes that the soil type along with soil moisture
and soil temperature can influence the distribution and abundance of
the cereal leaf beetle. A sandy-loam type soil that is well aerated
and stays relatively dry during the pupation period would definitely

favor the population increase in the cereal leaf beetle. Unfortunately

62
the soil types that are apparently favorable for the cereal leaf

beetle are also desirable types for most of the agricultural crops.

Experiment 13. Effect of Different Cage Sizes on Egg Production

 

 

Methods: This study consists of two separate tests. In Test 1,
field-collected summer adults that had been stored for 100 days at
38° F. while in Test 2 field-collected active spring adults were used.
In both tests three different types of cages l) a lamp chimney (3 inches
in diameter at the bottom and 7 inches in height), 2) a "medium"
plexiglas cage (8 x 8 x 12 inches), and 3) a "large” plexiglas cage
(15 x 15 x 15 inches) were used.

Thirty adults (15 pairs) were placed in each cage along with a
pot of ”Clintland 60" oat seedlings. All the cages were held in the
rearing room at 760 F., 75 percent relative humidity, and 16-hour
photoperiod. The plants were changed every other day and once every
three days in Tests 1 and 2 respectively and the number of eggs deposited
was counted. Test 1 was terminated after 23 days while Test 2 continued
for 37 days. The results were analyzed by means of an "F" test.

Results: Table 24 shows the results of the two tests during the
first 23-day period. An F-test indicated no significant difference in
the number of eggs produced in cages of three different sizes in both
tests.

In Test 1, however, the small lamp chimney cage seems to be
more effective in inducing earlier and more consistent egg production
in the case of overwintering adults. In a small cage the beetles are
kept close to the food plants and potential mates while they are fully

exposed to the light. Under such conditions, the beetles seem to become

63
more quickly reactivated. The same effect with lamp chimney cage has
been previously reported by Castro (1964).
TABLE 24.-—Effect of different cage sizes on egg production by field-

collected beetles stores in the laboratory and by field-collected
active spring adultsa

 

 

No. Eggs Laid per Cage
per 15 Females

 

 

 

 

Adults Cage Size I II Total Mean
Laboratory- Lamp Chimney 911 645 1,556 778
stored
adultsb Medium 8 457 465 233

Large 391 131 522 261
Field- Lamp Chimney 254 580 834 417
collected
spring Medium 611 779 1,390 695
adultsC

Large 521 639 1,160 580

 

F = Not significant in both tests.
aTest ended after 23 days.
bAdults had been stored at 380 F. for 100 days prior to the test.

CAdults had been collected in April in the field.

In the second test with field-collected active spring adults,
more eggs were laid in medium and large cages than in small lamp
chimney cages. For the active adults a larger space is apparently

needed for their various activities.

Influence of Biological Factors

 

The biological factors cited in this chapter include all the

"living organisms” such as predators, other individuals of the same

64
species, and host plants. Interactions occurring within and between
these organisms were studied. The results of the studies and analyses
of the results are presented below.

Experiment 14. Effect of Different Plant Densities on Development
of Larvae through to the Adults

 

 

 

Methods: The number of "Clintland 60" oat seedlings grown in
plastic trays of 5 x 8 x 2-1/2 inches in size was adjusted to 5, 10,
20, 40, and 80 plants per tray. The soil in each tray was first
covered with plaster of Paris and then with white silica sand following
the method of Connin, g£_§l: (1966b).

TWenty newly eclosed larvae were placed in each tray and they
were caged with a plexiglas cover of 5 x 8 x 11 inches in size. Three
replications were made for each treatment and all the cages were held
at 80° F., 70 percent relative humidity, and 16 hours photoperiod.

The number of adults emerged in each cage was recorded and the data
were analyzed using an F-test.

Results: The number of adults emerged from cages with original
ratios of 0.25 and 0.50 larvae per plant was significantly greater than
those emerged from the other three groups of cages. The difference is
highly significant according to an F-test (Table 25).

When the larval density in terms of the number of larvae per
seedling was transformed into logarithm and percent mortality into
probit, an apparent linear relationship was obtained. The details of
the transformations and a graphic representation are shown in Table 26

and Figure 8. According to the equation, LD occurs at the original

50
density of 0.5 larvae per plant or two 4—inch tall seedlings per

larva.

65

TABLE 25.--Effect of different larval densities on development of

larvae through to the adults

 

 

No. Adults Emerged
per Cage per 20 Larvae

 

 

 

No. Larvae Percent
per Plant 1 II III Total Mean Survival
0.25 20 8 16 44 14.7 73
0.50 16 16 10 42 14.0 70
1.00 O 2 9 11 3.7 18
2.00 2 O 0 2 0.7 3
4.00 0 0 0 0 0 0
F = 9.5337 (H. Significant) LSD 01 = 11.1

LSD 05 = 7.6

mmnm.o n u "ucmwowwmoOU coHuMNmuuoo

NomN.N + xwmmo.m u % uwooum “coHumdvm aowmmmuwmm

 

66

emw.n ooH Noo.H e nN.o ON m

wmw.o n.0m Hom.H N m.o ON ON
«om.m N.Hw ooo.~ H H oN ON
omq.¢ 0.0m mmo.0 om.o N ON 0%
wmm.¢ m.oN wmm.o mN.o e oN ow

 

Amv muHHmuuoz unmoumm muwaouuoz AxvoH mod Axv uanm Hod m>umq Hod om>uma .oz muamam .oz
nuanoum unmouom om>umq .oz muamHm .oz

 

ammo nod .02

 

 

 

ll ll

mufiamuuoa can mufimaoo Hm>uaH ammauoo awnmaoHumaomii.oN mqm<a

PROBIT : PERCENT MORTALITY (Y)

 

 

67

Probit Ya 3.0938X + 2.7962

1 A L 1 1 1 1 1 I

0.4 0.8 l.2 l.6 2.0
Log Density: No. Larvae per Seedling

Fig. 8 - Relationship between larval density and mortality.

68

The results of this study may not hold true under field condi-
tions because the plants usually outgrow the larvae. It was observed
in the field that young oat seedlings carrying more than one larva per
seedling were still able to grow. In the laboratory, however, original
number of at least two 4-inch tall seedlings per larva have to be pro—
vided at the beginning of the test to bring 50 percent of the first-
instar larvae through to the adult stage.

There were considerable individual differences among the larvae.
Certain individuals fed vigorously and were able to reach the adult
stage even at an original density of two larvae per seedling or 0.5
plants per larva. Intraspecific competition, in this sense, exists
among the larvae of the cereal leaf beetle especially when the amount
of food is limited. No cannibalistic behavior was observed among the
larvae even at the highest density.

Klomp (1964) stated that competition for food is generally re-
garded as the most common type of competition. Sang (1949) reported
occurrence of such competition among the larvae of Drosophila. Crombie
(1944) and Andersen (1960) listed increase of the mortality rate among
larvae and pupae as one of the consequences resulting from an increasing
competition among larval insects. Figure 8 clearly shows the increase
in mortality among the larvae with decrease in the amount of available

food per larvae.

Experiment 15. Effect of Different Adult Densities on Egg Production

 

 

Methods: Three separate tests were involved in this study.
General procedures employed in all three tests were about the same.

Fifty 4-inch tall ”Clintland 60” oat seedlings per pot and thirty

69
4-inch tall "Hudson" barley seedlings per pot were used in Test 1 and
Tests 2 and 3 respectively. Adults used in Test 1 had been stored at
38° F. for 110 days prior to the test while those used in Tests 2 and
3 were collected in the field in late April of 1966 when a few eggs
were observed.

Five different adult densities, 10, 20, 30, 40, and 50 adults
per lamp chimney cage were chosen for this study. Each cage contained
an equal number of males and females. A11 prepared cages were held in
the rearing room at 78° F., 75 percent relative humidity, and l6-hour
light period. The plants were changed every other day in Test 1 and 2,
and once every four days in Test 3. The number of eggs deposited on
the plants and the mortality of the adults were recorded. The data
were analyzed using an F-test.

Results: The total number of eggs laid per cage and per female
in three tests are shown in Tables 27, 28, and 29. The differences in
egg production at five different adult densities were not statistically
significant in all three tests according to an F-test.

An earlier observation indicated that an active spring adult
required at least one 4-inch tall fresh seedling supplied in every two
to three days for an adequate feeding and oviposition. Theoretically
with an average of 50 seedlings per pot and two-day renewal intervals,
50 adult beetles could be supported without hindering their egg laying
capacity as far as plant factors, the amount of available food and
oviposition sites, are concerned.

The adults used in Test 1 had been stored in the laboratory and
were unmated prior to the test. Table 27 shows that the total egg

production per cage as well as that per female is highest at the

70

TABLE 27.-~Tota1 number of eggs laid per cage and that per female at
different adult densities-:Test la

 

 

No. Eggs per Cage
or per Female

No. Adults

 

 

 

Measure per Cageb I II Total Mean
Per Cage 10 838 631 1,469 735
20 1,229 2,190 3,419 1,710
30 736 1,259 1,995 998
40 1,142 1,403 2,545 1,273
50 1,126 552 1,678 839
Per Femalec 10 209 179 388 194
20 197 330 527 264
30 150 159 309 155
40 83 136 219 110
50 112 34 146 73

 

F = 3.3466 (N. Significant)

aField-collected summer adults after 110 days of storage at
38° F. Plants changed every other day. Test ended after 106 days.

b .
1:1 sex ratio.

CEgg counts based on female days.

71

TABLE 28.-—Tota1 number of eggs laid per cage and that per female at
different adult densities—-Test 2a

 

 

No. Eggs per Cage
or per Female

 

 

 

No. Adults

Measure per Cageb I II Total Mean

Per Cage 10 376 666 1,042 521
20 854 539 1,393 697
30 1,387 1,047 2,434 1,217
40 389 913 1,302 651
50 823 551 1,374 687

Per Fema1ec 10 100 224 324 162
20 160 164 324 162
30 159 131 290 145
40 32 106 138 69
50 64 52 116 58

 

F = 2.5611 (N. Significant)

aField-collected active spring adults collected in April, 1966.
Plants changed every other day. Test ended after 42 days.

b .
1:1 sex ratio.

CEgg counts based on female days.

72

TABLE 29.—-Tota1 number of eggs laid per cage and that per female at
different adult densities--Test 3a

 

 

No. Eggs per Cage
or per Female

 

 

 

No. Adults
Measure per Cageb I II Total Mean
Per Cage 10 478 842 1,320 660
20 637 1,209 1,846 923
30 779 696 1,475 738
40 453 238 691 346
50 527 467 994 497
Per Femalec 10 112 213 325 163
20 119 150 269 135
30 92 90 182 91
40 56 18 74 37
50 37 51 88 44

 

F = 4.5802 (N. Significant)

aField-collected active spring adults collected in April, 1966.
Plants changed once every four days. Test ended after 72 days.

b1:1 sex ratio.

cEgg counts based on female days.

 

 

73
second lowest density and original density of 20 beetles per cage. An
increase in fecundity of the female with an increase in density from
10 to 20 adults per cage is probably due to a stimulatory effect re—
sulting from a slight crowding in the case of unmated adults. At the
lowest density the total egg production per cage is lowest of all but
the fecundity of individual females is second highest. As the density
increases from 20 to 30, 40, and 50 adults per cage, the fecundity of
females decreases accordingly. This decrease in fecundity is not due
to the shortage of food, but apparently due to overcrowding of the
adults in a limited area and space.

The fecundity of females in Test 1 is generally higher than that
in Tests 2 and 3 at all density levels. The reason is simply that the
laboratory-stored adults survived much longer than the field-collected
spring adults that had been exposed to variable natural environment
prior to the test and brought into a confined laboratory conditions.
With the unmated laboratory-stored adults and about 50 seedlings with
two—day renewal intervals, the optimum density level of the adults for
the maximum egg production seems to be 20 adults per lamp chimney cage
that has approximately seven square inches of area and 49 cubic inches
of space.

The adults used in Tests 2 and 3 were active spring adults col—
1ected in the field. They had apparently mated in the field. The
only difference in Tests 2 and 3 was the renewal period of food plants.
Fresh seedlings were supplied every other day in Test 2 and once every
four days in Test 3. The largest egg production per cage was observed
at the medium density of 30 adults per cage in Test 2 and at 20 beetles

per cage in Test 3. The egg production per female was greatest at the

74
two lowest density levels in Test 2 and at the lowest density in
Test 3. The fecundity of females gradually decreases as the density
increases up to 40 adults per cage and then it seems to level off.
The fecundity is generally higher in Test 2 than in Test 3 except at
the lowest density. This difference is obviously due to the difference
in renewal period of food plants in the two tests. A slight crowding
did not seem to favor egg production with the adults that had already
mated prior to the test.

Surprisingly, even under highly crowded conditions, only a few
eggs deposited on the plants were damaged by the adults. The damage
to the eggs was purely accidental and no egg cannibalism was observed
in this insect. The main causes of the decrease in fecundity with
increased density level seem to be: 1) a proportional reduction in
the amount of available food and oviposition sites and 2) a distur-
bance of copulation and oviposition act resulting from more frequent
body contact. A decrease in the rate of copulation, a disturbance of
the oviposition act, an excessive contact between individuals, and
reduction in the amount of food available to individual insects have
been reported by MbLagan (1932) and Crombie (1942) as contributing to
reduced egg production by Tribolium sp.

Survival of the adults was slightly better at the lowest density
than at the rest of the densities in all tests. However, no significant
adult mortality due to high adult density was observed. The majority
of females died after mating and laying eggs. A few adults survived
for much longer period than the others. These surviving ones were
found to be either males or unmated females. A small number of field-

collected spring adults in Test 3 survived for over 100 days; beyond

75
the 10th of August. These beetles, therefore, may be able to survive
for two years as was reported by Megalov (1927) and Hodson (1929) in

Europe.

Experiment 16. Amount of Feeding, Egg Production, and Survival of

 

 

the Adults on Oats and Barley

 

Methods: This study consists of two separate tests. Adult
beetles that had been stored at 43° F. for 65 days and two different
host plants, "Clintland 60” oats and "Hudson" barley were used in
Test 1. Thirty adults were placed in each lamp chimney cage containing
30 seedlings of oats or barley. Three replicated cages were made for
each host plant. Three additional caged pots without beetles were also
prepared for oats and barley and these pots were later used as check
pots for computation of the amount of feeding. All the pots were then
held in a growth chamber adjusted to 800 F., 70 percent relative
humidity, and 16 hours light period.

The plants were changed once every two to three days and the
number of eggs deposited on the plants and that of live and dead
beetles in each cage were counted. The amount of feeding on fresh
weight basis was calculated by measuring the difference in the weight
of seedlings that had been fed and that had not been fed by the beetle.
The seedlings were cut uniformly at the level of soil surface for
weighing.

In Test 2, the same two varieties of oats and barley were used
to test oviposition preference by field-collected active spring adults.
Three pots each of oats and barley were placed side by side in an
oviposition cage (14-1/2 x 16 x 16 inches) that contained about 150

adults. Exactly twenty—five 4-inch tall seedlings were left in each

76
pot. The oviposition cage was held at 78° F., 75 percent relative
humidity, and 16 hours light period. The plants were changed daily
for ten consecutive days for egg counts and the data were analyzed
using a t-test.

Results: The results of this experiment are shown in Table 30.
The amount of feeding and the egg production were greater in oats than
in barley. The differences, however, are not statistically significant
according to a t—test.

The total amount of feeding per beetle was 860 mg. in oats and
466 mg. in barley on fresh weight basis. The amount also includes the
water loss and other weight losses due to the feeding damage. The
method employed, however, would satisfy the preliminary nature of this
test. The amount of feeding per beetle roughly corresponds to eight
oat and 5.4 barley seedlings of 4-1/2 inches in height.

More than twice as many eggs were laid on oats as on barley
even though the difference is not statistically significant. More
detailed study on oviposition preference between oats and barley were
conducted in the second test. The egg production seems to be correlated
with the amount of feeding. Table 30 also indicates that a greater
number of eggs was laid between the 10th and 20th days in this group
rearing. The mortality of adults at the end of a 45-day test period
is much higher in oats than in barley. This is probably due to a
greater egg production on oats than on barley since the majority of
adults usually die when oviposition activity ceases.

The total amount of leaf tissue consumed per beetle in this
test is considerably lower than that estimated by Castro_g£ual. (1965).

Their report of 25.9 mg. of leaf tissue per beetle per day is nearly

 

onEom Hod mHumoo you mHmEmm you mHumoo you

 

77

 

 

 

 

 

wwwo O.NN mmcHHOmmm ¢.m wwwm «.0m mwcHHpoom w
m.OH¢ owe O.mow Oow Hmupa

m.Ho O.m in m.wm O.HH mN me

m.oo O.mH NH N.Ne O.N¢ mu O8

m.mo O.mN mN w.mq O.Nm mo mm

N.NN 0.0m mo H.Hm m.wm no on

N.ON m.mo mm w.mm m.nNH ON mN

m.mw N.ON co m.mo N.OOH HmH ON

n.0w n.mNH OHH 0.0m m.qu mON mH

m.mw O.Hn eHH 0.0m 5.5m OeH OH

H.Hm O.m Om ¢.ww m.wH No m
Ha>H>u5m owmo Hod A.w8v oHumom you Hm>H>Hom ammo Hod A.wav mHuoom you msz
unmouom mwwm .oz mom .us< unmouom mwmm .oz pom .u8<

onumm mono
ammo no you

.m one on monoum moHuooo wmoH Hmouoo mo Hw>H>usm mam .coHuosooum wmo .wcHooow mo ucooa<ii.om MHm<H

78

twice as much as 13.2 mg. per beetle per day in this test. The reasons
for such difference could be due to the facts that l) the beetles used
in this test were not as active as field-collected spring adults and
2) the feeding activity sharply decreased after the 20th day.

In the second test the adult beetles were exposed to both oats
and barley in the same cage. The results of the test are presented in
Table 31.

TABLE 31.--Oviposition of eggs on oats and barley by female cereal
leaf beetles

 

 

 

 

Days
Host 1 2 3 4 5 6 7 8 9 10 Total Mean
Oats 172 200 166 152 119 89 265 140 65 95 1,463 146.3

Barley 115 129 131 128 88 44 204 86 47 87 1,059 105.9

 

t = 8.5885 (H. Significant)

A t-test showed a highly significant difference between the
number of eggs deposited on oats and that laid on barley. The number
of eggs on oats is consistently higher than that on barley throughout
a ten-day test period. This test clearly indicates that the cereal
leaf beetle prefers oats to barley for oviposition. The results con-
firm the report made by Wilson and Shade (1964a) that oats are pre-
ferred to barley or wheat for oviposition.

Experiment 17. Oviposition of Eggs on Oat Seedlings with Different
Heights and Densities

 

 

Methods: "Clintland 60” oat seedlings of three different size

groups, 2, 4, and 6 inches in height, were obtained by adjusting the

79

planting date. For each size group, three pots containing different
numbers of seedlings were prepared. In the first pot 25 seedlings, in
the second 50, and in the third pot 75 seedlings were allowed to remain.
All nine pots were placed in an oviposition cage that contained about
150 active spring adults. The cage was held at 78° F., 75 percent rela-
tive humidity, and a l6-hour light period. The plants were changed
daily for five consecutive days and the number of eggs laid was counted.
The data were analyzed using a Chi—square test.

Results: The results on the number of eggs deposited on plants
with different combinations of height and density are shown in Table 32.

TABLE 32.--Oviposition of eggs on oat seedlings of different heights
and densities

 

 

Plant Height in Inches

 

 

 

No. Plants

per Pot 2 4 6 Total
25 98 95 98 291
50 78 82 96 256
75 74 159 111 344
Total 250 336 305 891

 

Chi2 = 1.57 (N. Signif.)

A Chi-square test indicated no significant difference in the
number of eggs found among different combinations of plant height and
density. However, the total number of eggs deposited on plants with
75 seedlings per pot and that on 4-inch tall plants are slightly greater
than the others. Castro,_g£nal. (1965) reported that more eggs are

deposited on 4 to 4-3/4-inch tall seedlings than on smaller or taller

80
plants. This experiment, however, does not show any definite relation-

ship between plant height and egg deposition.

Experiment 18. Effect of Different Male-Female Combinations on Egg_
Production

 

Methods: This study consists of two separate tests. Adults
used in Test 1 were field-collected summer adults that had been stored
at 38° F. for 130 days and were not mated prior to the test. The
beetles used in Test 2 were field-collected active spring adults and
'most of them had probably mated before they were collected for the
test.

Six different sets of female—male combinations, 4/1, 2/1, 1/1,
1/2, 1/4, and 1/0 were used in both tests. The first set of 4/1 in-
dicates that four females and one male were placed together in a lamp
chimney cage containing about 30 "Clintland 60" oat seedlings. Each
set was replicated twice in both tests. All the cages were then held
at 780 F., 75 percent relative humidity, and a 16-hour light period.
The plants were changed every other day until the last female died and
the number of eggs deposited was recorded. The data were analyzed
using a F-test.

Results: Table 33 and 34 show the results of the first and
second tests respectively. The results on the total number of eggs
laid per combination and that per female for field-collected beetles
that had been stored in the laboratory and field-collected active
spring adults are presented graphically in Figure 9.

The difference in the number of eggs laid per female in cages
with different male-female combinations is statistically not significant

in both tests. The total egg production per combination as well as

81

TABLE 33.--Fecundity of females in cages with different male-female

combinations

 

 

 

 

 

 

 

 

 

 

 

*Normal eggs.

No. Eggs Laid per Female
per Cage
No. Female/Male
per Cage I II Total Mean

4/1 37 46 83 41.5
2/1 170 152 322 161.0
1/1 631 505 1,136 568.0
1/2 172 98 270 135.0
1/4 43 38 81 40.5
1/0 129* -- 129 129.0
F = 15.1431 (N. Significant)
*All eggs did not hatch.

TABLE 34.--Fecundity of field-collected active spring females in cages

with different male-female combinations
No. Eggs Laid per Female
per Cage
No. Female/Male
per Cage I II Total Mean

4/1 190 157 347 173.5
2/1 195 204 399 199.5
1/1 127 127 254 127.0
1/2 240 126 366 183.0
1/4 122 355 477 238.5
1/0 42 211 253* 126.5

8 8

N
O
0

Mean Total No. Eggs per Combination

82

r _.° Mated

... Unmated

 

 

 

 

. C b)

g 400 ~

11’

i h

a"! O.

‘25 200 . ..................

E ....‘.,.' "no“... .................... . ................... . Ma'ed

,2 ..-' ........ . .......

g i- \ /

2 . ° Unmated

IIO I24 l:? 1" Zil 4”

Female: Male Combination per Cage

Fig. 9 — Mean total number of eggs produced per combination (a) and that per female (b) in cages
with different male-female combinations in previously mated and unmated adults.

83

that per female for unmated adults, however, are largest in cages con—
taining one female and one male (Table 33). Fecundity of the female
decreases as the ratio deviates from 1/1 to either direction.

The trend of the curves shown in Figure 9 is difficult to ex-
plain. One logical explanation for a gradual decline in fecundity in
2 female/1 male and 4 female/l male combinations compared to that in
1 female/l male could be as follows. Possibly only one female out of
2 or 4 females in 2/1 and 4/1 combinations did mate and the total
number of eggs laid per cage actually represents the number of eggs
laid by one female and not by all 2 or 4 females. The reason for a
decline in egg production with increased males in 1 female/2 male and
1 female/4 male combinations is probably due to a decreased chance for
an effective copulation from disturbances by other males or there might
have been an excessive copulation of a single female by 2 or 4 males
in the same cage. A total of 129 eggs were produced by an unmated
virgin female but none of them hatched. Mr. Patrick Brennan of Michigan
State University also reported his observation on unfertile eggs pro-
duced by virgin females (personal communication).

The trend observed in the second test with field-collected
spring adults is quite different from that in the first test. The
egg production per female remained steady in all cages while the number
of eggs produced per cage increased with the increase in the number of
females from 1 to 2 to 4 (Figure 9). An average of 126 eggs were pro-
duced by an isolated female. All of the eggs were normal in viability.

A further investigation on the influence of different sex
ratios on fecundity of individual females is needed. The results

obtained from this experiment, however, seem to indicate that different

84
sex-ratio combinations in a given unit area or space prior to the
initial mating influence the fecundity of individual females while it
is no longer influential in the mated females.

Experiment 19. Predation of Cereal Leaf Beetle Eggs by a Native
Coccinellid Predator

 

 

 

Methods: Eight pots of oats containing fresh cereal leaf
beetle eggs were obtained from the rearing program (Connin, 35.31:,
1966a). The number of eggs in each pot was counted and the plants
were caged with lantern globes. One coccinellid was placed in the
first cage, two in the second, four in the third, and eight coccinellids
in the fourth cage. Each treatment was replicated twice and the
number of eggs remaining in each cage was counted after 1, 2, and 4
days.

Results: A native coccinellid predator, Coleomegilla maculata

 

_lgggi Timberlake, has been reported as an important predator of the
cereal leaf beetle eggs in Michigan by Castro (1964) and Castro, g£_§l,
(1965). The results of this experiment are shown in Table 35.

A single coccinellid consumed an average of 19 to 76 eggs during
the first 24-hour period. The table indicates that the number of eggs
consumed per coccinellid per unit time decreased as the time progressed
from 1 to 2 to 4 days and also with a gradual increase in the number
of coccinellids per cage from 1 to 2, 3, and 4. In both situations the
number of eggs available per coccinellid gradually decreased thus
causing a decline in predation efficiency by the coccinellid.

Even with a single coccinellid per cage, 82 to 86 percent egg
[Predation occurred in 4 days. With 2 and more coccinellids per cage

853 to 99 percent egg loss was observed in 2 days and 99 to 100 percent

85

egg consumption by the coccinellid in 4 days. 9: maculata lengi

 

Timberlake seems to be an efficient predator of the cereal leaf beetle
eggs under a confined laboratory condition. It was also observed to
feed on the cereal leaf beetle larvae in the laboratory when no other
prey was available. Its feeding habit of possessing a variety of prey,
however, would certainly reduce its efficiency as a predator of the
cereal leaf beetle eggs under field conditions.

TABLE 35.--The number and percent of cereal leaf beetle eggs consumed
by a coccinellid predator

 

 

No. Coccinellid per Cage

 

 

 

 

 

 

l 2 3 4
Days after -————-———- ——-—-——-—-
Test Began I II I II I II I II
1 A 125 139 74 79 42 42 23 24
B 44 76 48 56 21 32 19 22
C 35 55 65 71 51 76 84 93
2 A 81 63 26 23 21 10 4 2
B 17 14 25 20 16 9 3 1
C 49 65 99 96 89 97 97 97
4 A 54 49 1 3 5 1 1 l
B 46 24 1 2 4 l l 1
C 86 82 100 99 99 100 100 100

 

A: No. eggs available per coccinellid.
B: No. eggs consumed per coccinellid per given period.

C: Percent eggs consumed per coccinellid per given
period (cumulative).

86

Diapause Studies

 

According to Castro E$_§13 (1965) the cereal leaf beetle seems
to have only one generation a year with an obligatory diapause under
field conditions in Michigan. This implies that the beetle remains
inactive for nearly nine months a year in the field.

To find a means by which the newly emerged summer adults can
be prevented from going into diapause or the diapausing beetles can
be quickly reactivated for continuous reproduction is essential for
rearing of the beetle in a year-round research program. The author was
mainly interested in the influence of physical factors, especially
temperature and photoperiod, on the induction and termination of dia-
pause in this insect.

Experiment 20. Egg Production by Newly-Emerged Summer Adults After
a Brief Egposure to Extreme Temperatures

 

 

 

Methods: Newly emerged summer adults were treated in the
following ways.

A. -10° F. for 1 minute followed by 1200 F. for 2 minutes.

B. -lO° F. for 1 minute.

C. 120° F. for 2 minutes.

D. 120° F. for 2 minutes followed by -100 F. for 1 minute.

T. No treatment (80° F. constant).

Each treatment consisted of two replicated lamp chimney cages
each containing 20 summer adults (10 pairs). After the treatments
were made all the beetles were held at 80° F., 75 percent relative
humidity, and 16-hour photoperiod during a 60-day test period. The

"Clintland 60" oat seedlings used as host plants were changed once

87
every four days, the number of eggs deposited was counted, and the
data were analyzed using an F-test.
Results: As Table 36 indicates the egg production in all treat-
ments is extremely irregular and inconsistent.

TABLE 36.-—Egg production by newly emerged summer adults after a brief
exposure to extreme temperaturesa

 

 

No. Eggs per Cage
per 10 Females

 

Days First Eggs

 

Treatmentb I II Total Mean Observed
-10°/120o F. 0 470 470 235 50
-10° F. 470 0 470 235 25
120°/-10o F. 203 0 203 101.5 37
1200 F. 103 0 103 51.5 54
80° F. Const. o 1 1 0.5 60

 

F = 0.3846 (N. Significant)
aTest terminated after 60 days.

bExposure time: 1 minute at -100 F. and 2 minutes at 1200 F.

Egg production by the treated adults seems to be somewhat
higher than the untreated adults at 800 F. constant. An F-test, how-
ever, indicated no significant difference in egg production among the
five different treatments. The first eggs were observed in 25 to 60
days depending on the treatment. In general, the total egg production
in all treatments was low and inconsistent, and no conclusive evidence
of continuous and consistent egg laying by newly emerged adults could

be observed from this experiment. All the eggs laid by the newly

88
emerged adults were normal in a sense that the percentage hatching is

comparable to that of the eggs laid by spring or overwintered adults.

Experiment 21. Egg Production by Field-Collected Summer Adults After
a 30—Day Storage Period at Low Temperatures

 

Methods: The summer adults used in this experiment were col-
lected in the field on July 18, 1965. The beetles were exposed to
different low temperatures for varying period of time as follows.

A. 380 F. for 15 days followed by 320 F. for 10 days followed

by 150 F. for 5 days.

B. 38° F. for 15 days followed by 32° F. for 15 days.

T. 38° F. constant for 30 days.

Thirty adults (15 pairs) were placed in each of three replicated
cages for each treatment. Following the treatments all the cages were
held at 80° F., 75 percent relative humidity, and l6-hour photoperiod.
The plants (oats) were changed every other day and the number of eggs
laid was counted. The data were analyzed using an analysis of
varience method.

Results: The results presented in Table 37 show that the egg
production in this experiment is considerably greater and more con-
sistent than that observed in previous experiment. This is probably
caused by the fact that the beetles used in this experiment had been
subjected to low temperatures for 30 days prior to the test.

The mean egg production in all treatments is not significantly
different from one another when the data were analyzed using an F-test.
Castro,_g£ El. (1965) reported that the hibernating beetles were
successfully induced to reproduce by subjecting them to temperatures

of 25° - 43° F. for 15 - 25 days prior to exposing them to higher

89
temperatures of 750 - 800 F. In fact, some of the newly emerged adults
can be induced to lay eggs even without subjecting them to low tempera-
tures as it is shown in Tables 43, 44 and 45. An important question is
how soon the beetles would start laying eggs and how consistently they
would lay. The egg production in this experiment is obviously low
compared to that by spring adults and other beetles that had been
stored at 380 F. for more than 30 days (Table 38).

TABLE 37.——Egg production by field-collected summer adults after an
exposure to low temperatures for 30 daysa

 

 

No. Eggs Laid per Cage
per 15 Females

 

 

Cold First Eggs
Treatment I II III Total Mean Laid in Days
38°/32°/15° F.b 761 744 223 1,733 578 7
38°/32° F.C 480 564 643 1,687 562 8
38° F.d 360 209 992 1,561 520 11

 

F = N. Significant
aTest ended after 30 days.

b15 days at 380 F., 10 days at 32° F., followed by 5 days
at 15° F.

C15 days at 38° F. followed by 15 days at 32° F.
dEntire 30 days at 380 F.

Experiment 22. Egg Production by Summer Adults after varyingiPeriods
of Storage at 38° F.

 

 

 

Methods: This experiment consists of two separate tests. In
Test 1, the summer adults stored at 38° F. were taken out after 30, 50,
70, 90, 130, 160, and 220 days. Fifteen pairs of adults were placed

in each lamp chimney cage and two replicated cages were made for each

90
storage group. All the cages were then held at 800 F., 75 percent
relative humidity, and 16 hours light period. "Clintland 60" oat
seedlings were used as host plants and they were changed every other
day for egg counts. The data on cumulative egg production during the
first 30-day period were analyzed using an F—test.

In Test 2, only one pair of beetles were kept in each lamp
chimney cage. The beetles used in this test had been stored at 38° F.
for 50, 80, 110, and 130 days prior to the test. Also used in this
test were field—collected overwintering adults and active spring
adults that had been collected in the field in February and April
respectively. The number of eggs laid during their life time was re-
corded. Adl the rest of the procedures were exactly the same as in
Test 1. The data were analyzed using an F-test and 95 percent confi-
dence limits for the mean egg production per female for each group
were calculated.

Results: Table 38 shows the total egg production per cage per
15 females that had been held at 38° F. for varying periods of time.

As the storage period increases from 30 to 90 days the egg
production also increases accordingly. The peek egg production is at
90 days of storage at 38° F. and the egg production gradually decreases
from there on. An F-test indicates that the mean egg production is
significantly different from one another at the 5 percent level. The
least significant difference (LSD) also shows that the egg production
at 90 days is significantly greater than that at 30 days at the l per-
cent level and that at 50 and 70 days at the 5 percent level. The egg
production at 90, 130, 160, and 220 days is not significantly different

from one another. Active spring adults collected in the field laid as

91
many eggs as the others that had been stored at 38° F. for 130, 160,
and 220 days. From this analysis it is apparent that at least 90 days
of storage period seems to be required for the summer adults to com-
plete their diapause development at 380 F.

TABLE 38.--Egg production by summer adults after varying periods of
storage at 38° F.

 

 

No. Eggs per Cage
per 15 Females

 

 

 

 

Storage at Days First
38° F. in Days I II Total Mean Eggs Laid

30 361 222 583 292 11

50 515 358 873 437 13

703 570 831 1,401 701 7

90 1,263 1,983 3,246 1,623 6

130 1,632 848 2,480 1,240 5

160a 1,620 1,218 2,838 1,419 4

220a 1,026 1,134 2,160 1,080 5

Spr. Adultsb 1,383 1,044 2,427 1,213 3
F = 4.3846 (Significant) LSD 01 = 1,265
L8005 = 835

aLaboratory-reared adults. All the rest were field-collected
and laboratory-stored adults.

bField—collected active spring adults collected in early April.

Data not included in analysis.
In order to obtain more detailed information regarding egg
laying capacity of individual females, the beetles were raised singly

or in pairs in lamp chimney cages. The results of this test shown in

92
Table 39 are generally in agreement with those observed in previous
test with group culture (Table 38).

Again the egg production increases with an increase in storage
period up to 110 days and it declines with further increase in the
storage period. The largest egg production was observed among the
beetles that had been stored for 110 days at 38° F. and one female in
this group produced 1,251 eggs during a 153—day period. This may
well be considered as an exceptional case but it indicates a high re—
productive potential possessed by this species.

Although the multiple mating is the rule in this species
(Castro, SE 31., 1965; and Merino, 1966), a single mating seems to be
generally sufficient for a full production of eggs. One isolated
female after the first mating laid 465 eggs while another female pro-
duced 629 eggs. In the latter egg hatching was normal in the first
400 eggs, the rest of over 200 eggs were unfertilized, and egg laying
stopped completely after laying a total of 629 eggs. By reintroducing
an active male into the cage the same female laid additional 293 eggs
of normal viability. This observation generally confirms an earlier
report made by Dr. R. F. Ruppel of Michigan State University that
there were no significant differences between the number of eggs nor
the viability of the eggs produced by the isolated females and
isolated pairs (unpublished data in 1965). The multiple matings, how-
ever, seem to increase egg production as well as viability in some
females that survive for a long period of time.

One isolated virgin female laid 129 sterile eggs without mating
while the other female did not lay eggs until an active male was in-

troduced into the cage. Normally the female beetles produce about 35

93

.cmwfinoflz .cmwamu Home ooafi mo kum< maumo cw wouooafioo mufiovm magnum o>wuu<o

.cmmwnoflz .coHHmw ammo coma .m humounom co wouoofiaou muasum wcwuoucw3uo>o

n

.vwma whoa ammo mam HmcoHuwvvm .mama m>wuom cm wcwosuouucfimu

 

 

 

hm .mwwm mmo mcwmmfi Houwm commmo wcwmma wwm .wcwuma umun man “down woumaoma mamaomm
m.mom u mo.amq
q.¢a¢ u Ho.nmq Auamowwwcwwm .mv mmom.¢ u m
mqum -- w.6NH H65 .. o4 me am ooH NmN 6mm 66436< manuam
am-om 03-3 0.5Hm Nom.H -- Nmfi «Hm HAN own mo¢ owe 66H=6< 666603
6m-oH m m.moq w-.H -- -- -- -- mm mom fine omfi
mmfiumo NNIm m.Hmo 0mm.m u: «m mom mod mam mmmm Hmm.~ OHH
wauoa m 0.05H Nmm I: I: In :1 In mmH mam om
Hman wuq m.mo wm¢ «H mm oq Hm qm mm meg on
mama CH mamaom was; wwwm and: amuoH HH> H> > >H HHH HH H mama cw .m can
mo huH>owcoA umuflm mama um omeOum

mwmo nod mumsmm won mama wwwm .oz

 

4'

TI,

 

 

mmfimaow woumHOmH was mufimm woumHOmw kn vaH ammo mo Hogans Houoall.mm mqm<H

94
percent of unfertilized eggs even in the presence of males in the
laboratory (Table 46).

The data presented in Table 39 were analyzed using an F-test.
The differences in the mean egg production by adults of different age
groups are highly significant. As the least significant difference
(LSD) values indicate the adults after 110 days of storage at 38° F.
laid significantly greater number of eggs than those laid by winter and
spring adults and by the adults that had been stored at 380 F. for 50
and 80 days. The difference between the mean egg production by the
adults stored for 110 days and that by the adults after a l30-day
storage period is not statistically significant.

Table 40 shows 95 percent confidence limits for the mean egg
production per female. According to the table the adults that had been
stored for 110 days are capable of laying from 163 to 1,099 eggs per
female while active spring adults would lay from 28 to 225 eggs per
female. A wide range in the number of eggs produced by different in-
dividuals is reflected in exceptionally large coefficient of variation
values. Such high values could be resulted from individual differences
in egg-laying capacity and longevity and also due to inadequate samples.
Ninety-five percent confidence limits for the mean egg production by
the adults that had been stored at 38° F. for 80 and 130 days are not
presented in Table 40. The calculated values for these two groups of
adults did not reasonably represent the mean egg production because of
small number of samples.

The mean egg production of 126 eggs per female in the spring
adults is slightly higher than 96 eggs per female reported by

Dr. R. F. Ruppel of Michigan State University (unpublished data). The

95

 

 

0.363 v 1 v 6.00 0.00 0.603 660-06 63100 000010
0.006 v 1 v 3 603 0.60 0.030 006-003 60104 666003
0666350 0.36 0.006 306-00 003
0.000.3 v 1 v 6.063 6.00 0.306 360.3-60 033
0666050 6.60 0.603 03~-mm3 00
0.603 v 1 v 0.60 6.00 0.06 663-63 06
quHQ mUCmUHNCOU o\6mm COHumHHm> NO Cmmz mwcmm umHmEmm .2an C..." .m own

60636000600

nod wwwm .02

um owmuoDm

 

 

mamsmm Hod coHuuscoum wwm some you muwsfia mucmcwwcoo ucmoumd o>0m|mumcwzlu.o¢ mqm<H

96
latter's report of 96 eggs per female, however, was based on his field
data. Castro, e£_gl: (1965) reported that approximately from 150 to
400 eggs per female is expected in the laboratory. In Europe, it is
reported that one female lays up to 50 eggs during a season in England
(Hodson, 1929), 50 to 150 eggs in Rumania (Knechtel and Manolache,
1936), and 100 to 150 eggs in Italy (Venturi, 1942).

The oviposition rate of the female was relatively constant
during an entire egg-laying period. The rate of 15 to 20 eggs per
female day is most common. One female produced up to 27 eggs in a
24-hour period. These figures are generally higher than those reported
by Hodson (1929) of l to 3 eggs a day, by Knechtel and Manolache (1936)
of 2 to 18 eggs, by venturi (1942) of 3 to 12 eggs, and by Borg (1959)
of 5 to 6 eggs per female day in Europe.

Diapause development in the cereal leaf beetle seems to be com-
pleted by the end of December under field conditions in Michigan.
Hibernating adults collected in the field in early January of 1966 for
an observational purpose became immediately active and produced a con-
siderable number of eggs in the laboratory. Tables 38 and 39 seem to
indicate that once their diapause development is completed younger
adults are more vigorous and produce more eggs than older ones whose
reproductive activities are hindered and delayed by unfavorable envi-
ronmental conditions. Therefore, in the region where spring comes
early in March the adults would lay more eggs and the subsequent larval
damage would be much more severe than in the region where spring comes
late in May. Even in a given region, the same phenomenon would be
observed in a particular year when spring comes early. Kadocsa (1916)

Iffikarted that early warm spring favors population build—up in this species.

97

Experiment 23. Mortality of Field-Collected Summer Adults Stored
at 38° F.

 

 

Methods: A large number of summer adults were collected in the
field during their peak emergence period. TWO hundred adults were
placed in each plastic container (3—1/2 x 3—1/2 x 3 inches) with a
piece of moist paper towel. These containers were then stored for
later uses in a cooler that was adjusted to 38° F. The date the
beetles entered the cooler, the date they were removed from the cooler,
and the number of dead and live beetles were all recorded in a record
book.

The collection and maintenance of the beetles were done by
Messrs. David L. Cobb and George Lawson of Entomology Research Divi-
sion, USDA, and Mr. John C. Arnsman of Michigan State University. The
writer is grateful for their aid in furnishing valuable data for this
study.

Over 180—day period, a total of 264 containers having 52,800
beetles have been examined. For each duration-of—storage category a
median duration in days was calculated and this was converted to
logarithm (X). The conversion was made because the observed points
fit better on a semi-log scale. The percentage mortality for each
category was converted to Probit using a table provided by Finney
(1952). A linear regression equation was calculated from logarithm
time (X) and Probit mortality (Y).

Results: The time—mortality relationship at a constant storage
temperature of 38° F. for field-collected summer adults is shown in
Table 41 and Figure 10. All observed points fall very closely to the

Eflnpirical regression line. LD 50 was calculated to be 146.8 days at

00mm.o n u "0:000000000 :0006000060
0Nm0.6 I xN00N.6 u M 000000 "c00umsvm a00mmouwmm

 

 

98

 

 

 

0N.06 0NO0.00 60m 0muoH
mm.0 0.00 060N.N 0.mw0 06 @001000
wm.0 0.60 0N6N.N m.600 00 0001000
mm.0 0.N0 0moN.N 0.m00 06 m00|000
mw.6 6.06 N000.~ 0.660 mm 0001060
m0.6 0.0m 00N0.N 0.mm0 O6 O60I0N0
60.6 N.Nm 0mmo.m 0.000 0N om0u600
00.6 0.00 060m.0 N.6m 00 OO0IN0
mm.m o.N0 6000.0 0.00 m 00:00
N0.m o.m 0000.0 o.~0 N N0

va 00006000: 0u00muuoz x .mo0 Axv mmmn c0 voc0amxm mmma :0
"00noum unmoumm coHumudm :M0noz muoc0muaoo .02 .m 000 um c00umusa

.m own

ucmumcoo 06 000006 mu0svm 008536 now m0£mCO0uw0ou hu00MuuoEImE0u 0006030060 0cm wm>uomnoll.06 mqm<H

99

@N

.u_ can 0:223 8 032m 3.300 .2555 of 50 £02281. 05258-05: .33an 0:0 003300 I o— .3".
.1600 8 8060 06.3

6N NN O.N 0.. w._ 6... N._

4 1 1 1 4 ‘ J I 1 1 ‘ 4 I

 

 

(A) AlllVlUOW 1N3033d21|808d

100
38° F. and other time-mortality values obtained from the equation are

presented in Table 42.

TABLE 42.--Empirical time-mortality values for summer adults stored at

 

 

 

380 F.
Percent Duration at 38° F. Percent Duration at 38° F.

Mbrtality in Days Mortality in Days
5 59.7 50 146.8

10 72.8 55 157.2
15 83.3 60 168.6
20 92.6 65 181.2
25 101.5 70 195.5
30 110.2 75 212.2
35 118.9 80 232.6
40 127.7 85 258.7
45 137.1 90 295.9

 

The survival of the adults at 38° F. seems to be better than
that at 43° F. Castro, gt_al: observed 30 percent mortality after 90
days and 50 percent after 160 days of storage at 43° F. Their percent
mortality figures are obviously higher than those shown in Table 42
during the same periods of storage at 38° F. The higher percent
mortality at 43° F. seems to be due to a higher metabolic activity
than at 38° F. A further investigation is obviously needed to improve
the present storage methods so that a greater number of summer adults

could be preserved for much longer period of time.

101

Experiment 24. Egg Production by Field—Collected Summer Adults under
Different Photoperiods

 

 

Methods: The summer adults used in this test were collected in
the field in early July. Thirty beetles (15 pairs) were placed in each
lamp chimney cage and two of these cages were placed in each of six
growth chambers that were adjusted to 0, 8, 12, 16, 20, and 24 hours
light periods. All the chambers were maintained at 800 F. and 75
percent relative humidity. "Clintland 60" oat seedlings used as host
plants were changed every other day for egg counts. The data were
analyzed using an analysis of varience method.

Results: The total egg production per cage during a 38-day
period and the mortality of adults at the end of the test period are
shown in Table 43.

The table indicates that the egg laying pattern under different
photoperiods is very much similar to that observed in the overwintered
adults (Table 14). The largest egg production was again observed in
the region of 16 hours photoperiod. Under a constant 12—hour light
period no eggs were produced by the beetle. The results of this experi-
ment confirms an earlier report made by Castro, 35 31. (1965). The
differences in the mean egg production by the adults under different
photoperiods, however, were not significant according to an F—test.
Use of three or more replicated cages could have yielded more con-
clusive results.

The summer adults collected on the same day did not lay eggs
in a large screen cage (15-1/2 x 15-1/2 x 15-1/2 inches) even under
the favorable environmental conditions. The author was unable to

detect the causes for such difference in reproductive activity in the

102

00660000000 .z u 0

 

 

0.NN I: o o o 0 6m
6.0m om mm 00 00 o om
6.0m 00 ~00 6N0 060 606 00
0.0a II o o o 0 N0
0.00 6 m0 000 00 600 0
0.00 0 00 m00 M6 000 o
0000 mm 00000 0000 00 0002 00000 00 0 00000 .0zu6m 000

00330600: 0300< 0 0360 6000 06000

 

.003 00 00000000000

m00080h 00 00a 0w00
00a 0000 wwwm .oz

 

 

000000 0000

000100 0 w00030 000000000000 000000000 00003 000300 008830 00w00s0 0030: 00 0000030000 wwmul.06 mqm<e

103
summer adults. The amount of light penetrating through the cage or
the light intensity inside the cage as well as the cage size as was
demonstrated in Experiment 13 (Table 24) seem to have at least some
effect on inducing egg production in the summer adults. Even in the
small lamp chimney cages the adults are extremely sluggish and all the
activities remain at the minimum level.
Experiment 25. Egg Production by Newly-Emerged Summer Adults for

Three Successive Generations under Different Photo—
period Combinations

 

 

 

 

Methods: The eggs laid by summer adults under a 16-hour light
period in a preceding experiment were divided into three groups. The
first group of eggs was held under lZ-hour light period, the second
group under 24-hour light, and the third group under a l6-hour light
period. Temperature and relative humidity in all three growth chambers
were maintained equally at 800 F. and 75 percent respectively. Larvae
hatching from these eggs were allowed to develop in each growth chamber
until they reached the adult stage.

All the newly emerged adults under 12- and 24-hour light periods
were immediately transferred to a constant l6-hour light period. Thirty
adults (15 pairs) were placed in each lamp chimney with fresh "Clintland
60" oat seedlings. The plants were changed every other day and the
number of eggs laid and adult mortality were recorded. When the first
generation adults started laying eggs in their respective cages, the
eggs were transferred back to 12- and 24-hour light periods under which
the parent beetles were raised. As in the first generation, the
immature stages were raised under 12—, 24-, and l6-hour light periods

and all the adults were held under a constant 16-hour photoperiod.

104
The same procedure was used for the third generation and the data were
analyzed using a Chi-square test.

Results: The overall results of egg production by three con-
tinuous generations of summer adults are shown in Table 44. The first
generation adults were raised from the eggs laid by field-collected
summer adults. Only those eggs that were laid early in their egg
laying period were kept for further investigation on possible non-
diapausing strain of the beetle.

TABLE 44.--Egg production by newly-emerged summer adults for three
continuous generations under different light periods

 

 

No. Eggs Laid per 15
Females per Generation

 

 

 

Photoperiod in Hrs. 50% Mortality of
per 24-Hr. Cycle 1st 2nd 3rd Total Females in Days
12-16a 2,104 730 312 3,146 56-41-44b
24-16 1,077 532 435 2,044 30-53-53
16 Const. 640 167 11 818 89-61-60
Total 3,821 1,429 758 6,008

 

Chi-square = 302.1006 (H. Significant)

aImmature stages raised under 12-hour light and adults under 16-
hour light period.

bPercent mortality for the lst, 2nd, and 3rd generations
respectively.

A Chi-square test indicates that there are significant differ-
ences in the number of eggs produced by three successive generations
under three different light period combinations. The table shows that

the egg production decreases from one generation to the next and also

105
with a change in light period from a 12—16-hour combination to l6—hour
constant. The adults seem to be more responsive to the changing light
period than to the constant photoperiod. General vigor of the newly-
emerged adults seems to decrease from one generation to the next. Even
though some of the adults did oviposit viable eggs, all of the adults
remained very much inactive throughout entire test period. A non-
diapausing strain of the beetle did not exist, at least in a sample
of population dealt in this experiment.
Experiment 26. Egg Production by Field-Collected Summer Adults in

Laboratory and Natural Environment with and Without
Hiding Places

 

 

 

 

Methods: The summer adults used in this experiment were col-
lected in the field near Galien, Michigan on July 11, 1966. Fifteen
pairs of adults were placed in each of six lamp chimney cages. Hiding
places were provided in three cages by means of a piece of rolled
paper towel that was suspended above the soil surface. No hiding
places were provided in the other three cages. All six cages were
then held at 780 F., 75 percent relative humidity, and a 16-hour light
period.

Another set of six cages with and without hiding places were
held outside the laboratory building in East Lansing, Michigan until
October 11, 1966. "Clintland 60" oat seedlings used as host plants
were changed once every four days for egg counts and the data were
analyzed using a t—test.

Results: Table 45 shows quite obvious results of this experi-
ment. The summer adults collected on the same day from the same field
produced eggs in the laboratory but not in the natural environment

during the period from July 11 through October 11, 1966.

106

TABLE 45.——Egg production by the summer adults in the laboratory and
natural environment with and without hiding places

 

 

No. Eggs Laid per Cage
per 15 Females

 

 

 

Hiding
Environment Place I II III Total
Laboratory With 0 124 45 169
Without 5 61 82 148
Outdoor With 0 0 0 0
Without 0 0 0 0

 

With 23: without hiding places: t = 0.4000 (N. Significant)

Laboratory vs: Outdoor: t = 2.5046 (Significant)

Castro, 35 El. (1965) reported that egg production by summer
adults can be more easily induced in lamp chimney cages with a minimum
of hiding places. As the table indicates the egg production was not
influenced by the presence or absence of hiding places. Even under
the laboratory conditions a considerable variation in the numbers of
eggs produced among replicated cages, especially between the first and
the remaining two replicates. Such variation could be caused by
difference in the number of females that were actually laying eggs and
also by the individual differences existing among the females. Approxi-
mately 10 percent of the adults remained moderately active in all cages
even when hiding places were provided. The author's observation in-
dicated that there was a small proportion of summer adults that were a
little more active than the others and these active adults seemed to
be the ones that produced eggs. Egg production by these small number

of adults, however, was extremely irregular and inconsistent.

107

The difference in egg production between indoor and outdoor
cages was apparently due to the differences in environmental conditions.
Day length gradually decreased from 13:56 hours on August 15 to 12:31
hours on September 15. This range of light period is apparently not
favorable for the summer adults to produce eggs (Expt. 24). Average
minimum temperature also decreases considerably from 55.70 to 47.20 F.
respectively on the same dates.

The existence of the second generation under field conditions
has been reported by Averin (1914) in Russia and by Wilson and Toba
(1963) in Indiana. The author's experimental results, however, show
that the presence of the second generation in Michigan is very unlikely.
A univoltine life cycle with an obligatory diapause reported by

Castro 35 21: seems to be the rule in this species.

Life Tables and Net Reproduction Rates

 

Experiment 27. Age-Specific Life and Fertility Tables Based on
Laboratory and Field Mortality Data

 

 

 

Methods: This experiment was conducted in the laboratory that
was adjusted to 78° - 80° F., 65 - 75 percent relative humidity, and
l6-hour light period. The first table is a generalized life table of
the beetle under present rearing conditions in the laboratory. The
table form was adapted from Morris (1963) and Embree (1965). A total
of 3,987 eggs were examined for hatchability. These eggs were obtained
from the rearing room. Only 670 larvae were kept for further studies
because of handling difficulties. The larvae, pupae, and newly emerged
adults were reared in lamp chimney cages. Inactive summer adults were

stored at 38° F. for 90 days following the method developed by

108
Connin, gt_§1: (1966a). The age interval was divided into six distinct
categories, egg, larva, pupa, newly emerged active adult, diapausing
adult, and post—diapause active adult. The number of individuals
dying during each age interval and possible causes for the mortality
were investigated.

The second and third tables were constructed to estimate the
net reproduction rate for the laboratory and field populations of the
cereal leaf beetle. The table form was adapted from Birch (1948) and
Laughlin (1965). The second table was constructed for the laboratory
population of adults stored at 380 F. for 90 days. Information on the
mortality rate was derived from the first table. The age-specific
fertility column (mx) was computed by multiplying a constant 0.324 to
each of the corresponding numbers in preceding fx column. The con-
stant 0.324 was derived by dividing the survival rate of the eggs
0.648 by two. Assuming 1:1 sex ratio, 32.4 percent of the eggs laid
per female would be the fertile female eggs.

The third table was made for the field population. The active
spring adults were collected in April of 1966 in the field before they
started laying eggs. The adults were brought into the laboratory and
their fecundity and survival were recorded under the laboratory con-
ditions. An important assumption made before constructing this table
was that the survival and fecundity rates observed in the laboratory
approximate sufficiently close to that would occur in the field. The
following estimates on survival rates of different stages of the beetle
at Galien, Michigan were made by Dr. R. F. Ruppel of Michigan State

University (unpublished data in 1965).

109

 

Stage Survival Rate
Egg 0.50
Larva 0.34
Pupa 0.91
Summer Adult 0.85
Overwintering Adult 0.40

Table 48 is based on Dr. R. F. Ruppel's estimates on the sur-
vival rates under field conditions in 1965 season. A constant used in
this table was 0.25 which is exactly one—half of 0.50, the survival
rate of the egg stage in the field. In other words, only 25 percent
of the total number of eggs laid by a female would be viable female
eggs. The net reproduction rate (R0), the rate of multiplication in
one generation, was calculated by simply adding all lxmx values.

Results: Table 46 shows a generalized age-specific life table
for the cereal leaf beetle that was reared under the laboratory condi-
tions of 780 - 800 F., 65 - 75 percent relative humidity, and a l6-hour
light period (Connin, g£_§l:, 1966a). It was assumed that a 90-day
storage period at 380 F. is necessary to break a diapause in this
beetle.

As the table indicates the highest mortality was observed in
the egg and pupal stages. Most of the egg mortality was simply due to
the production of unfertilized eggs by female beetles and it accounted
for about 35 percent of the total number of eggs produced by the females.
Approximately 24 percent mortality occurred in the larval stage from
unknown causes. The larval mortality could have been due to a mis-
handling of young larvae and a slightly crowded condition in small

cages. Thirty-nine percent of prepupae entering the soil for pupation

110

 

 

Now sage< manuam
o>fluo<
mam.o o.wa ms czoaxas new .eaoe
.oHSDmHoa 304
new uH3n<
wswmsmdmwa
Hmm.o m.mH qn c30cxc:
Hon ufisn< uoassm
m>wuo¢
o~o.o o.mm NmH czoaxcs new
coHumasa muaumamum
mm¢ mmsm
Hem.o m.mm mmH czochD
mqo m>umq
mqo.o N.mm Nmm czocxcs pom
voNHHHuummaD
ooo.~ wmm
x awcuwz xH mo x wcfiuso xv you x mo mafiaawwmm Hm>umucH mw<
mumm Hm>w>usm owmucoouom mm xv magma .oz manwmcommom nobomm om m>HH< .02
x
Aullmule "xm H\e ooH xv axe xa x

H + xH

 

 

mcofiufivcoo kHOumuoan nova: manomn mama

Hmouoo mcu you wanna

mung onwaumAm-mw<--.oq mamas

111
died during the pupal stage. One positive cause for the mortality was
premature pupation. Most of these partially developed prepupae con-
structed complete pupal cases in the soil but failed to make further
development into pupae and adults inside the pupal cases.

During a two-week feeding period, about 18 percent of the newly
emerged summer adults died from unknown causes. Again the confined
caged condition could be one of the contributing factors for the
mortality. There was a negligible number of deformed adults that died
in a few days after emergence. The mortality of diapausing adults
during a 90-day storage period was approximately 19 percent. The
mortality in the diapausing adults was mainly due to low moisture level
and development of molds in storage containers. Some of the dead
adults contained unidentified species of nematodes. Starting with a
convenient number of 1,000 eggs, 202 post-diapause adults can be ob-
tained under the present laboratory conditions.

Table 47 shows net reproduction rate for the laboratory popula-
tion under above mentioned rearing conditions. The table is based on
the mortality data given in previous table (Table 46) and a 90-day
diapause period at 380 F. was assumed. It indicates that the laboratory
population increases about four times in one generation. The net re—
production rate, however, can be increased to some extent by 1) im-
proving rearing techniques and 2) shortening of diapause period using
a synthetic hormone reported by Connin §£_§13 (in press), for instance.

Table 48 was constructed using the field mortality data prepared
by Dr. R. F. Ruppel (unpublished data in 1965). Active spring adults
collected in the field in early April were brought into the laboratory

and the survival and fecundity rates of the females were measured in

112

 

 

 

 

om u omm.m amm.m~ mm.~m annoy
o¢o.o o¢N.H oo.¢ mmo.o mmnwm
Hmo.o wo~.~ oo.m oqo.o wmumm
omo.o «mw.a mo.m mqo.o mNaoN
qofi.o mma.m ¢o.m omo.o omumm
moo.o mmo.~ mm.m coo.o mmlqm
moo.o NNo.o mm.H doH.o #Nnmm
Hom.o wmo.o mn.wH w¢H.o mmumm
Nmm.H omm.~ qm.¢m #mH.o NNIHN
q~o.~ mwo.m em.ma me.o HNION
o~o.o 0mm.o mo.H mmH.0 omlma

.m omm um coauma mmmuosm Nom.o mauo
nowumd wcfimmow moaowumaolumom n¢m.o 01¢
mowmum manumEEH Hom.o «Io
ooo.H o
x comm aw x um mHmEmm x um mama x mw< um
mama mwmm mamEom you mama wwwm wwwm mamamm mamamm onu mo mxooz ca

mfiwuumm .oz HmuOH onEmm mHHuumm .02 now mam: .oz oumm ~m>H>usm Hm>uouaH ow<

xsxa Aemm.o x xu uvxa xm xH x

 

 

muOumuoan mno CH whom om How .m omm
um concum coon pm: umsu maumon mama ammumo onu How manmu huwfiwuumm mam mafia owmfiuommlmw<ul.m¢ mqm<H

113

 

 

 

 

om u Ham.o mma.mm Hm.oma Haney
«Ho.o mmm.~ qu.m moo.o mm|¢m
mNH.o mmn.w mfi.mm «Ho.o qmlmm
mmm.o mHN.oH mw.o¢ mmo.o mmnmm
«mm.o omo.w o~.mm ¢m0.o mmlam
mom.o mm~.o mm.¢m mqo.o anion
voHumd mmsmmmwn €mo.o omloH

wofiuma wcwpoom mocowumEolumom «m~.o oHuw

mowmum musumEEH me.o wlo

ooo.H o

x comm a“ x on onEmm x on mama x mw< um

mama mmwm mfimsmm you mama wwwm wwwm mamaom mamaom mnu mo mxmo3 :«

maauumm .oz Haney

xExH

onEwm oHHuuwm .02 com mam:

X

Aqmm.o x xm uvxa m

mumm Hm>w>usm

xa

Hm>umucH mm<

an

 

 

moan mufiflmunos vawww

magma coHumHSQOQ UHmHm mnu How mfinmu huwuwuumw new mafia oamwommmlmw<ul.m¢ mqm<H

114
the laboratory. Assuming the survival and fecundity rates in the
laboratory approximate sufficiently close to those under the field
conditions and the mortality data reported by Dr. R. F. Ruppel are
relatively accurate, then the calculated net reproduction rate for the
field population in Galien area is close to one. This means the popu-
lation size remained very much constant in one generation from 1965 to
1966.

The calculated net reproduction rate of .941 for the field
population is surprisingly low. It is, however, quite possible that
the field population is actually increasing from one generation to the
next but the reproduction rate is underestimated because of following
reasons. 1) The adult sample used in this test did not adequately
represent the field population, 2) the survival and fecundity rates
were more or less suppressed in laboratory cages, 3) an excessive
handling of the adults, or 4) the survival rates made by Dr. R. F.
Ruppel could have been somewhat too low. Obviously more studies on

this phase of population dynamics are needed.

General Behavior and Sex Ratio

 

Laboratory observations showed that the overwintered adults
require a minimum of 550 F. for an effective initial mating and ovi-
position. This observation confirms the report made by Castro, g£_31,
that the adults seem to be active when the temperature reaches 55° F.
or more. Knechtel and Manolache (1936) reported 500 F. as the thresh-
old for the initiation of adult activity in spring. The flight of
overwintered adults was observed when temperature reached about 680 F.

in the laboratory. Hodson (1929) and Balachowsky's (1963) reports of

115
flight occurring at 620 F. seems to be somewhat lower while 720 F.
reported by Castro, gt_al, (1965) is slightly higher than the author's
observation at about 680 F.

The adult beetles after 110 days of storage at 380 F. laid their
first eggs in 4 days at 800 F., in 10 days at 700 F., and in 16 days
at 600 F. The egg laying was extremely poor and irregular at 600 F.
while it was fairly consistent at 700 F. Multiple mating seems to be
the rule in this species as was mentioned by Castro, EELEE: (1965) and
Merino M. (1966). The existence of definite homosexual behavior in the
males has been reported by Merino M. (1966) but the author was unable
to observe any mating activity taking place between two males. Fre-
quently an active male mounts on the back of another male, attach
its protruded aediagus below the elytra of the second male, and remain
in that position for some time. Some other males even mount on dead
beetles. Homosexual behavior in this sense does exist in this beetle,
however.

Oviposition behavior of the female beetle is as follows. Prior
to oviposition the female while maintaining the sternum about 2 mm.
above the leaf surface moves up and down apparently to locate a proper
oviposition site. When the egg laying is imminent the female lowers
the abdominal tip to the leaf surface and an egg is deposited. If
the leaf width is relatively narrow as in oats (3-4 mm.), the ovi-
positor falls right on the midvein of the leaf. This is the main
reason why majority of the eggs are deposited along the midvein in
oats.

The first egg is usually laid on the basal portion of the

leaves. The female upon depositing the first egg moves about 1/2 inches

116
up and deposits the second one, and so on only when the plant is in
single-leaf stage. When the second leaf appears the female tends to
deposite the eggs in a chain-like fashion one right next to the other
near the lower portion of the first leaf. The eggs are usually laid
singly or in pairs when enough host plants are provided. One female
was observed to lay four eggs in a row one after another in the
laboratory in about five minutes. It requires from approximately 30
seconds to two minutes from pausing for oviposition to actual deposi-
tion of an egg. If the female continues to lay eggs at this speed,
the rate would be from 30 to 120 eggs per hour. The highest oviposition
rate observed in the laboratory, however, was 27 eggs a day per female
and normally from 10 to 20 eggs per female per day during the peak
oviposition period. These figures are generally higher than those re-
ported by European workers. It has been stated that one female in
spring lays l to 3 eggs a day in.England (Hodson, 1929), 3 to 12 eggs
in Italy (Venturi, 1942), 5 to 6 eggs in Sweden (Borg, 1959), and 2

to 18 eggs per day in Rumania (Knechtel and Manolache, 1936).

Experiment 28. Distribution of Eggs on Oat and Barley Seedlings

 

Methods: Thirty active spring adults were placed in each lamp
chimney cage containing "Clintland 60" oats or "Hudson" barley. The
seedlings were at a growth stage where the second leaf was about to
emerge at the time of the test. Three replicated cages were used for
each host plant. All the cages were held at 800 F., 75 percent rela-
tive humidity, and 16 hours photoperiod. The plants were changed
every other day and the number of eggs deposited on the apical, central,
and basal third of the leaves and those occurring singly, in twos, in

threes, in fours, and in fives or more were recorded.

117

Tests with oats and barley were conducted at different times
using different beetles and a direct comparison of the original data
for oats and barley could not be made. However, the percentage figures
for one host could be reasonably compared with those for the other
host plant.

Results: As Table 49 indicates over 99 percent of the eggs
were deposited on the upper leaf surface in oats while about 62 per-
cent of the eggs were laid on the same leaf surface in barley. Nearly
68 percent of the eggs were laid singly and about the same proportion
of the eggs were deposited on the basal third of the upper leaf surface
in oats. In barley, on the other hand, about 45 percent of the eggs
occurred singly and also on the basal third of the upper leaf surface.

The proportion of eggs laid on the lower leaf surface was con-
siderably greater in barley than in oats. A Chi2 test showed that
significantly greater number of eggs were laid singly and on the basal
third of the two host plants. This experiment clearly demonstrates
that the female beetles prefer the basal third of oat and barley leaves
for oviposition. The reason why the female beetles prefer a particular
leaf surface or portion of a particular host plant is not clearly
understood. Oviposition behavior of the females seems to be at least
partly influenced by density of the beetle and physical conditions of
the host plant. The physical conditions include such factors as stage
of growth, condition of the leaf surface, and width and shape of the
leaves. At higher density, the basal third of the plants are usually
less damaged compared to the upper portion of the leaves and the ovi-
position activity of the female is less disturbed at the basal region

of the plant.

118

TABLE 49.—-Number and percent eggs occurring in different numbers on
different parts of oat and barley leaves

 

 

No. Eggs in a Upper Leaf Surface Lower Leaf Surface

 

 

Row and Part

 

 

Host of Leaves No. Eggs Z Eggs No. Eggs Z Eggs
Oats 1 1,254 67.86 10 0.54
2 444 24.03 2 0.11
3 93 5.03 0 0
4 40 2.16 0 0
5 or more 5 0.27 0 0
Basal 1/3 1,255 67.91 1 0.05
Central 1/3 446 24.13 7 0.38
Apical 1/3 135 7.31 4 0.22

 

Chi-square = 22.7142 (H. Significant)

 

 

 

Barley l 485 44.62 342 31.46
2 154 14.17 76 6.99
3 30 2.76 0 0
4 0 0 0 0
5 or more 0 0 0 0
Basal 1/3 489 44.99 179 16.47
Central 1/3 152 13.98 168 15.45
Apical 1/3 28 2.58 71 6.53

 

Chi-square

11.3247

(H. Significant)

 

119
The author's results are generally in agreement with those re—
ported by Castro, g£_31, (1965). The latter's figures are slightly
lower than those in Table 49 in that they found 98.5 percent of the
eggs on the upper surface of oat leaves, about 60 percent on the basal
third, and about 42 percent occurring singly on the upper leaf surface.

Experiment 29. Oviposition Behavior of Female Beetles on Oats with
Different Leaf Postures

 

Methods: It was learned from the preceding experiment that the
cereal leaf beetle lays a greater number of eggs on the upper surface
than on the lower surface of oat leaves. This experiment was intended
to see if such oviposition pattern would be influenced by different
leaf postures.

Exactly 25 "Clintland 60" oat seedlings of the same age group
were allowed to grow in each plastic pot of four inches in diameter.
The following pretest treatments were made on the oat seedlings in
three pots. 1) Leaves in the first pot were slightly broken at the
base and maintained horizontally to show their upper surface up,

2) leaves in the second pot were also maintained horizontally but with
their upper surface down, 3) leaves in the third pot were maintained
in normal upright posture.

Above three pots were then placed in an oviposition cage that
contained actively ovipositing spring adults. The oviposition cage
was held at 78° F., 70 percent relative humidity, and a 16-hour
photoperiod. The plants were changed daily for four consecutive days
and the number of eggs deposited on the upper and lower surfaces of

the leaves was counted. The data were analyzed using an F-test.

120
Results: Table 50 shows that different leaf postures did not

influence oviposition behavior of the female beetles.

TABLE 50.--Oviposition of eggs on upper and lower surfaces of oat
leaves with different leaf postures

 

 

No. Eggs Deposited

 

 

Leaf Leaf
Posture Surface I II III IV Total Mean
Horizontal, Upper 18 27 21 31 97 24.3
Upper Surface

Up Lower 4 0 1 0 5 1.3
Horizontal, Upper 32 31 16 76 155 38.8
Upper Surface

Down Lower 0 0 0 0 0 0

NOrmal Upper 23 24 10 31 88 22.0
Upright Lower l 0 0 0 l 0.3

 

2.0566 (N. Significant)

Leaf posture: F

Leaf surface: F 34.7238 (H. Significant)

No matter how the leaves stand and what direction the upper
surface of the leaves are facing, a significantly greater number of
eggs are laid on the upper leaf surface than on the lower surface in
oats. The difference in the number of eggs deposited on the upper
leaf surface and that on the lower leaf surface is highly significant
according an F—test.

Experiment 30. Sex Ratios of Laboratory-Reared and Field—Collected
Adults

 

 

Methods: A total of 1,781 spring and summer adults, laboratory-
reared and field-collected, were dissected under a binocular scope for

sex determination. The laboratory-reared spring adults denote the

121
beetles that had been stored at 380 F. for 145 days after their emer-
gence from the soil. A Chi2 test was used to analyze the data.
Results: Table 51 shows the results of analyses on the sex
ratio of four different samples.

TABLE 51.-—Sex ratios of field—collected and laboratory-reared spring
and summer adults

 

 

Source of Stage of

 

 

Samples Adults No. Female No. Male Total Chi2
Field Spring 361 239 600 24.806 (H.S.)
Summer 139 116 255 1.579 (N.S.)
Laboratory Spring 179 156 335 1.579 (N.S.)
Summer 322 269 591 4.753 (Signif.)

 

The number of females is consistently greater in all four
samples. The sex ratio of field—collected spring adults and laboratory-
reared summer adults was found to be significantly different from one
to one while that of the other two samples was proved to be not signif-
icant according to the Chi2 test. The reason why the former two
samples contained significantly greater number of females is not known.
It could be due to a "chance” factor such as a particular time of

collection or due to a larger sample size than the other two samples.

DISCUSSION

As in any other living organisms the development and multiplica-
tion of the cereal leaf beetle are directly and indirectly influenced
by the conditions of physical and biotic environments in which they
live.

Hibernating adults seem to be most resistant to cold temperatures
since they were able to survive for a prolonged period of time at 380 F.
(Table 42) while the eggs and larvae were unable to survive at 480 F.
for more than 5 and 11 weeks respectively. Diapause development can
take place at moderately low temperatures above 32° F. Castro 35 31.
(1965) reported that the winter survival of the overwintering adults
was highest at the ground level and no adults survived at 4 feet above
the ground. Mr. M. S. Gomulinski of Michigan State University (personal
communication) has reported that the temperature at the snow-covered
ground level near Galien, Michigan stayed around 32° F. during winter
months and did not drop far below 32° F. The author observed a con-
siderable number of adults under the roadside grasses in early March of
1964 when the temperature was still too low for the adults to fly.

Mr. John T. Hayward of Plant Pest Control Division, USDA, found a large
number of overwintering adults in the litter and duff samples near
Galien, Michigan in late winter of 1967 (unpublished report).

Based on these observations the most probable site for the

majority of overwintering adults seems to be the ground level that is

122

123
covered with snow. The layer of snow on the ground serves as an effec-
tive barrier and insulator and it protects the beetles from direct
exposure to the excessive cold during winter months. The adults over-
wintering under the loose bark or inside the cracks of fence post would
be directly exposed to freezing winter temperatures and a prolonged
exposure to such extreme temperature would eventually result in a high
overwintering mortality. The adults were unable to hang on to the
plants when temperature was dropped to 38° F. in the laboratory.

The heaviest winter mortality is expected in the area where
there is only a little snow on the bare ground and temperatures stay
well below 32° F. during the winter months. The winter kill will be
relatively low in the area where winter temperatures stay around 32° F.
and the right amount of moisture or free water is available to the
beetle. Diapause development in the cereal leaf beetle seems to be
completed by the end of December under the field conditions in Michigan
because the mating and oviposition activities of the overwintering
adults collected in January was comparable to those of active spring
adults in the laboratory (Table 39). Diapause development, therefore,
apparently proceeds during late fall and early winter months as was
indicated by Zolotarev (1947).

Fecundity of the female seems to be highest immediately after
the completion of its diapause development and it decreases gradually
as time progresses (Tables 39 and 40). In the area where the spring
comes early, the individual female would lay more eggs than in the
area where the winter is long and a cold spring prevails. In the

former area an early warm spring would certainly favor the population

124
build-up as was mentioned by Kadocsa (1916) while in the latter area
the maximum fecundity or egg production cannot be realized.

The overwintering beetles become active during the first warm
days in spring (Castro 35 31. 1965). From the author's observation it
is believed that at least some mating can take place in the overwintering
site before they move into the green grasses or other cultivated crops.
In the laboratory the mating often preceded the feeding activity. The
flight of the spring adults occurred freely when temperatures reached
680 F. or more in the laboratory. The flight temperatures of 620 F.
reported by Hodson (1929) and 62.60 F. by Balachowsky (1963) seem to
be a little lower than that observed by the author.

The multiple mating without any noticeable courtship behavior is
reported as the general rule in this beetle (Castro 35.31:: 1965 and
Merino, 1966). In the laboratory one female that was isolated from
the male after the first mating laid up to 629 eggs in an isolated
cage (Table 39). Out of 629 eggs about 400 eggs were normal in hatch-
ability and the rest of the eggs were all unfertilized. When a male
beetle was introduced into the cage, the same female laid an addi-
tional 293 eggs and the hatchability gradually increased. Another
female laid 465 eggs in an isolated cage. From these observations it
was concluded that the single mating would be sufficient for average
females to lay normal eggs during their life time. The multiple mating,
however, apparently stimulates oviposition activity and increases
hatchability of the eggs in some cases. There is a report of homosexual
mating behavior in this beetle (Merino, 1966) but the author was

unable to detect any incidence of actual copulation by two males.

125
An active male would mount on the back of another male, insert its
aedeagus below the elytra of the other male, and remain in that posi-
tion for some time. Such apparent copulatory behavior between two
males can be frequently observed upon a close look at the pair of the
beetles.

A complete cessation of movement by the larvae and adults
occurred at 38° F. but a slight movement was observable at 45° F. in
the laboratory. A noticeable feeding activity was observed at 500 F.
but it was negligible at 450 F. A.minimum of 55° F. seems to be re-
quired for an effective initial mating and egg deposition and at least
of 700 F. for more consistent egg deposition.

The reproductive activity of the spring adults is largely in-
fluenced by temperature, photoperiod, and relative humidity. The egg
production by the spring adults is greater at 80° F. than at 850 F.
(Table 9) and the optimum temperature for the spring adults seems to
be 800 F. The mean monthly temperatures recorded at Eau Claire Station
in Michigan are 48.3° F. in April, 59.10 F. in May, and 69.50 F. in
June. Majority of the eggs are laid in May (Castro SE 31., 1965) and
it is quite reasonable to assume that most of them are laid during day
light hours when temperature modified by the sunlight are sufficiently
high.

Photoperiod also influences the egg production in the spring
adults. The range of photoperiod favorable for the spring adults is
between 16 and 18 hours but the maximum oviposition rate was observed
under 18 hours of light period in the laboratory. Under field condi-

tions, however, the photoperiod never reaches 18 hours. Photoperiods

126
in Kalamazoo, Michigan are recorded as 13:22 hours on April 15, 14:36
hours on May 15, and 15:16 hours on June 15 and majority of the eggs
are laid between 14 and 15 hours of light period in the field. As
Table 15 shows egg production under l4-hour photoperiod is relatively
low compared with that under 16 and 18 hours of light periods. From
the fact that the spring adults lay most of their eggs during day hours
(Table 17) and the largest quantity under 16-18 hours indicate that the
cereal leaf beetle is definitely a diurnal and long-day insect.

The egg production by the spring adults is also significantly
influenced by relative humidity. The higher the relative humidity the
greater was the egg production in the laboratory test. The mean rela-
tive humidities are recorded at South Bend, Indiana as 57% in April,
46% in May, and 48% in June at 12:00 noon and those recorded at
Muskegon, Michigan are 58, 56, and 60% respectively at 1:00 P.M. These
data might be considerably different from the actual values that can
be expected near the micro-environment the cereal leaf beetle chooses.
The relative humidity as well as temperature in the actual habitat of
the beetle are expected to be somewhat higher than those recorded at
weather stations. The mean percipitation is highest (4.18 inches) in
June and followed by 4.08 inches in May and 3.88 inches in April
according to the data recorded at Eau Claire, Michigan.

The optimum environmental conditions, therefore, seem to be
800 F., 18 hours of photoperiod, and 95 percent of relative humidity.
Obviously such ideal constant conditions will never be attained in
nature and consequently a full reproductive potential of the cereal

leaf beetle will not be realized. The beetles may, in fact, be more

127
adaptive under such ”sub-optimum” conditions of natural field environ-
ment. The "sub-optimum" conditions could allow more flexibility and
this would provide a selective advantage for the maintenance of entire
population.

Fecundity and longevity of individual females vary widely.
Laboratory reared females after 110 days of storage period at 38° F.
laid from 34 to 1,251 eggs with an average of 631 eggs per female.
Field collected summer adults after 130 days at 38° F. deposited from
92 to 631 eggs with an average of 409 eggs per female. Overwintering
adults collected on February 9, 1966 in the field and stored for 48
days at 38° F. produced from 182 to 480 eggs with an average of 317
eggs. Lastly active spring adults collected on April 28, 1966 when a
few eggs were observed in the field laid from 40 to 256 eggs with an
average of 126 eggs per female under laboratory conditions of 800 F.,
16-hour photoperiod, and 75 percent relative humidity (Table 40).
Average number of eggs per female per season is reported as 50 by ‘
Hodson (1929), 50 to 150 by Knechtel and Manolache (1936), and 100 to
150 by Venturi (1942). The author's observation of 40 to 256 eggs per
female for active spring adults includes the figures presented by above
European workers. A report by Castro 35 31. of 150 to 400 eggs per
female per season at 800 F. is also confirmed by the author's labora-
tory test.

Individual females in isolated cages in the laboratory laid from
5 to 27 eggs per female per day with an average of about 20 eggs during
their peak oviposition period. These figures are expected to be some-

what lower under the field conditions. The rates of oviposition in

128
terms of the number of eggs laid per female per day are reported as l
to 3 by Hodson (1929), 2 to 18 by Knechtel and Manolache (1936), 3 to
12 by Venturi (1942), and 5 to 6 by Borg (1959) (Table 2).

Temperature seems to be the most important single factor which
directly controls the development of the cereal leaf beetle. The
maximum range of temperature for the development of the immature stages
of the cereal leaf beetle seems to be between 54° F. and 92.50 F. where
540 F. is the threshold for the development of pupae and 92.50 F. the
peak temperature at which the embryo develops at the fastest rate.
Thresholds for the development of egg, larva, pupa, and entire immature
stage were calculated using Uvarov's (1931) formula and a straight
velocity line method used by Matteson and Decker (1965). Based on the
authors repeated tests, the thresholds obtained using Uvarov's formula
seem to be more accurate than those obtained by the latter method
(Table 7). Knechtel and Manolache (1936) reported the thresholds of
development as 53.6° F. for the egg and larva and 48.2° F. for the
pupa. According to the author's observation and calculation the pupal
stage requires a higher threshold for the development than the egg or
larval stage and this is exactly the opposite to the data presented by
Knechtel and Manolache (1936).

Both Davidson's (1944) logistic curves and straight velocity
lines were used to express the relationship between temperature and
the rate of development of the egg, larva, pupa, and entire immature
stage. The reciprocals of the days required for the development of a
given stage form an S—shaped velocity curve when they are properly

plotted. Observed points follow very closely to the Davidson's logistic

129
curves throughout most of the temperature range except at 95° F. for
egg stage and 760 F. for all stages (Figures 2, 3, 4, and 5). At 95° F.,
the rate of development of the embryo has slowed down because of an ex-
cessively high temperature. Temperature in a growth chamber that was
supposed to be set at 760 F. apparently had not been maintained properly.
When the linear regression equation was used, the observed points does
not follow as close to the calculated lines as in the case of Davidson's
logistic curves (Figure 6). However, computation involved is much
simpler in the case of straight lines and they still give considerably
accurate estimates on the rate of development of a given stage through-
out most of the temperature range.

The author's data on duration of the development of different
stadia at various constant temperatures are generally in agreement with
those reported by Castro 25 31, (1965) at 80° F. and by Knechtel and
Manolache (1936) except the duration of pupal stage (Table 2). The
latter's report on the pupal stage of 5 days at 30° C. (86° F.) and
6 days at 26° C. (78.80 F.) seems to be more accurate estimation of
the pupal period since the author's observation was based on the period
from the day a prepupa enters the soil for pupation until the day it
emerges from the soil as an adult.

It was observed in the laboratory that the cereal leaf beetle
eggs cannot develop at constant temperature of 48° F. One hundred
percent mortality of the eggs occurred within 5 weeks while a complete
kill of the larvae was observed in 11 weeks at 48° F. This would in-
dicate that a high percentage of egg mortality can be expected in the

field if an early warm spring is followed by a prolonged cold spell of

130
48° F. or below. Mr. M. S. Gomulinski of Michigan State University
has reported a high mortality of early eggs in the field in April of
1966 mainly due to a long unseasonably cold weather that followed
immediately after a brief warm days in early spring.

Among the four major requisites listed by Klomp (1964) food and
oviposition sites seem to be the two main items for which the cereal
leaf beetle competes under certain laboratory conditions. Adult beetles
compete for both food and oviposition sites while the larvae compete
mainly for food. With laboratory stored adults the greatest egg pro-
duction was observed at the second lowest density of 20 adults per lamp
chimney cage with about 50 seedlings that were changed every other day
(Table 27). As the adult density increased the fecundity of the individ-
ual female decreased. As Crombie (1942) mentioned a slight crowded
density of 20 adults per cage might have caused some stimulatory effect
on the rate of oviposition than at the lowest density of 10 beetles per
cage.

In spring adults that were collected in the field after mating
had already occurred, the fecundity of the individual female was
highest at the lowest density of 10 adults per cage with 30 seedlings
that were changed every other day (Table 29). As the density increased
from 10 to 20, 30, 40, and up to 50 adults per cage, the fecundity of
the female gradually declined. The fecundity was slightly lower in
cages where the plants were changed once every 4 days than in cages
where the plants were changed every other day. The main causes for
the decline in egg production with increasing adult density seem to be

due to l) a reduction in the amount of food available to individual

131
beetle, 2) a reduction in the oviposition sites, and 3) an excessive
contact between individual beetles. Similar phenomena were observed
in Tribolium sp. by Chapman (1928), Park (1932 and 1933), McLagan (1932),
and by Crombie (1942).

The total number of eggs produced per cage, however, was greatest
at the density of 30 adults per cage when the plants were changed every
other day and at 20 adults per cage when the plants were changed once
every 4 days. An active spring adult was observed to destroy one 4-inch
tall seedling in two days. It is estimated that at least one 4-inch
tall seedling per adult per day is required for the beetle to feed and
deposit an adequate number of eggs.

The amount of food available has a direct effect on the develop—
ment and survival of the larvae. The mortality rate among the larvae
increased with an increase in the larval density (Figure 8). At least
two 4-inch tall seedlings are necessary for a newly hatched larva to
complete its development (Tables 23 and 24). The rate of feeding in
terms of the amount of feeding per individual per unit time is more
intense in adults than in larvae. The larvae, however, cause more
damage to the plants than the adults in the long run simply because
they become more numerous than the adults in the field. Dr. R. F. Ruppel
of Michigan State university estimated the actual yield reductions in
spring grains at 15 to 35 percent in Michigan (unpublished data).

The development and survival of the pupae are apparently in-
fluenced by soil type and soil moisture. A light, well aerated but
slightly moist soil is apparently preferred to the heavy and wet soil

for pupation in the cereal leaf beetle (Tables 19 and 23). This soil

132
factor may have a significant effect on the distribution of the cereal
leaf beetle in a given geographical area.

Mesnil (1931) stated that some new adults emerge in summer while
others stay in the soil until the following spring. vassiliev (1913)
and Vereshtchagin (1914), on the other hand, reported that all of the
new adults stay within the pupal cases in the soil until the following
spring. The author has examined numerous pupal cases during his entire
study period and was unable to detect any sign of new adults remaining
in their pupal cases. Those remaining in the pupal cases were either
dead or deformed ones.

Exposures of different stadia of the beetle to various tempera-
tures and photoperiods have failed to prevent the majority of summer
adults from going into diapause. Egg laying by the summer adults,
however, can be induced by keeping the beetles in a lamp chimney cage
at 800 F., l6-hour photoperiod, and 75 percent relative humidity. This
has been already demonstrated by Castro, 35 31. (1965). The beetles
even in the lamp chimney cage remained quite inactive throughout the
oviposition period and the egg production was extremely irregular and
inconsistent. These eggs were apparently produced by a small number
of females. Mr. T. L. Burger of Plant Pest Control Division, ARS,

USDA at Niles, Michigan reported that he and his colleague have success-
fully isolated a non-diapausing strain of the cereal leaf beetle from
the eggs laid by field-collected summer adults (personal communication).
Further systematic studies on genetic constituents of natural population
and a critical evaluation of adaptive value of the non-diapausing in—

dividuals are needed.

133

De Wilde and Boer (1961) stated that diapause in adult insects
is generally characterized by an inhibition in the maturation of eggs
associated with corpus allatum failure. More recently Kumararaj (1964)
and Hoopingarner,_g£.al. (1965) reported that the gonads of the female
beetle do not normally develop until they have been subjected to a low
temperature. Their statements do not seem to hold true, at least in
some females that lay eggs without having a low temperature treatment.

From these observations and experimental results (Table 45), the
cereal leaf beetle seems to be a univoltine species with an obligatory
diapause in the adult stage. The existence of the second generation
reported by Averin (1914) in Russia and Wilson and Toba (1963) under
field conditions in Indiana is very unlikely to occur under natural
conditions in Michigan. Certain field-collected active spring adults
(Expt. 15) laid eggs in July and survived well beyond the 11th of
August in the laboratory. The author did observe small larvae in early
August in the field but it is hard to believe that they were the second
generation. Dr. D. L. Haynes of Michigan State university also reported
that he observed numerous spring adults, eggs, and larvae in a late-
planted oat field in late June and July in 1967 near Galien, Michigan
(personal communication). The surest way of breaking diapause in the
cereal leaf beetle is to hold the beetle at 38° F. for at least 90 days.
Another promising method by which diapause can be readily terminated
would be the use of a synthetic juvenile hormone described by Connin,
_g£.§l. (in press).

The summer adults seem to be highly sensitive to high tempera-

tures. A 50 percent mortality of the adults occurred after a 7-day

134
exposure to 1000 F. A 100 percent mortality of the inactive adults
occurred within 6 hours at 1200 F. A high temperature treatment in
this sense may be useful in disinfestation of grains and hay crops un-
less the cost involved is too high or the quality of the crops changes
appreciably from such treatment.

After a brief feeding period the summer adults show a photo-
negative behavior and go into an inactive stage (Castro, st 31., 1965).
The main factor that induces such hiding behavior seems to be heat, a
combined effect of temperature and photoperiod (sunlight). Many beetles
reappear in the fall when the weather becomes cool (personal communica-
tion with Mr. M. S. Gomulinski). The summer adults seem to go into
aestivation in July, move in and out during cool days in the fall, and
then move into hibernation sites.

An age-specific life table was constructed for the beetle under
laboratory conditions (Table 46). This type of life table is very
unrealistic because such natural mortality factors as parasitization,
predation, and winter kill are not included in this table. However,
it still provides some valuable information regarding the survival and
mortality of the beetles in their different stages of development.

Based on a fertility table for the beetles that had been stored for 90
days at 38° F., the cereal leaf beetle multiplies about 4 times per
generation under laboratory conditions (Table 47). The net reproduction
rate can be increased to some extent by more careful handling of the
insect. The net reproduction rate for the field population was estimated
at .941 (Table 48). If we assume all the mortality data are accurate

and the field-collected spring adults reproduced faithfully in the

135
laboratory as they would in the field, the figure indicates more or
less a steady density level. It is, however, quite probable that the
low net reproduction rate of .941 could be due to the underestimation
of mortality and fecundity rates and possibly due to a continued aerial
application of insecticides during the past several years.

The distribution of the cereal leaf beetle is highly spotty and
shows an extremely discrete pattern under natural conditions (Castro,
EE.El:: 1965). Such distributional pattern seems to be influenced by
a micro-climate or micro-environment of a given habitat. The density
of the beetle often varies widely among closely adjacent fields. The
major factors which seem to influence the distribution and abundance
of the cereal leaf beetle are 1) natural enemies, 2) availability of
preferred host plants, 3) temperature, 4) photoperiod, 5) moisture,

6) wind, 7) soil, and 8) presence or absence of woodlots in the vicinity.

As in any other phytophagous species natural enemies would
regulate the population density of the beetle and distribution of pre—
ferred host plants would largely determine the distribution of the
beetle itself. Such climatic factors as temperature, photoperiod,
moisture, and wind have a direct influence on the development and sur-
vival of the beetle by one factor modifying the others. The beetle
activities are strongly affected by the wind. The adult beetles
usually stay low near the ground on windy days and the population
density is generally low in open windy fields. The wind also influences
the distribution of the beetle. It carries the beetles for a consider-
able distance (Wilson and Ruppel, 1964; and Shade and Wilson, 1964).

Soil type and moisture would have a significant effect on the survival

136
of the pupae. Wbodlots would serve as an effective aestivation and
hibernation sites as well as an effective windbreak.

All the experiments presented in this paper were conducted in
the laboratory. The author hopes that the results of these experiments
would serve as the basis for future field experiments. Continuous
studies are obviously needed especially in the area of population
dynamics of this species. All mortality factors should be analyzed
more carefully and precisely in order to establish more complete life
tables under various conditions. A close evaluation of native enemies,
orientation system, soil factors, and perfection of artificial media

are highly desirable and would certainly facilitate future studies.

SUMMARY

During a two and a half year period from 1964 to 1966, a series
of laboratory studies were conducted on the reproduction, development,
and survival of the cereal leaf beetle under various specific conditions.

A large number of field—collected summer adults were stored at
38° F. for the year round rearing and research purposes in the labora-
tory (Connin,.gtnal., 1966a). A linear regression equation was cal-
culated to express the relationship between the storage period at 38° F.
in days and the mortality of the beetle. A LD.50 for the summer adults
stored at 38° F. was found to be 146.8 days (Table 42).

Diapause development in the summer adults seems to be completed
after 90 days at 38° F. The largest egg production was obtained with
the beetles that had been stored for 90 days at 380 F. Those which had
been held at 38° F. for 70, 50, and 30 days or 130, 160, and 220 days
laid progressibly fewer number of eggs (Table 38). Diapause development
of the field populations appears to be completed by the end of December
since the beetles collected in early January immediately started laying
eggs when they were held under the laboratory conditions.

The initial flight by the overwintered adults occurred freely
at 68° F. in the laboratory. A.minimum of 55° F. seems to be required
for an effective initial mating and egg deposition in the overwintered

adults. The egg laying was extremely irregular at 600 F. but it became

137

138
more consistent at 70° F. Laboratory observations showed that the
adults and larvae were completely immobilized at 380 F. but they were
able to hang on to the plants at 45° F. without any noticeable feeding
activity.

Random samples of field—collected spring adults and laboratory-
reared summer adults contained a significantly greater number of females
than males. The sex ratio in the samples of field-collected summer
adults and laboratory-reared spring adults was not significantly dif-
ferent from 1:1 (Table 51).

With unmated adults (unmated before the test), the egg produc—
tion, total number as well as per female, was greater in a lamp chimney
cage containing 1 female and 1 male than in cages with 2/1, 4/1, 1/2,
or 1/4 female/male combinations. With already mated adults (already
mated before the test), however, the total egg production per female
remained about the same in all female/male combinations and the total
egg production per combination increased almost proportionately with an
increase in the number of females from 1 female/1 male to 2 females/

1 male and to 4 females/l male. An unmated female laid as high as 631
eggs and the mated female laid up to 355 eggs per female. A.virgin
female laid 129 eggs but none of them hatched. A sex ratio of 1:1
prior to the mating seems to be ideal in the cereal leaf beetle

(Table 34).

A laboratory reared female after 110 days of storage period at
38° F. laid up to 1,251 eggs during her life time of 153 days. The
female was kept with a male in a lamp chimney cage at 800 F., 75 percent

relative humidity, and 16 hours photoperiod. Another female, isolated

139

from the male after the first mating, ceased egg laying activity after
depositing 629 eggs. Approximately the first 400 eggs, however, were
normal and the rest of the eggs were all unfertilized. When the same
female was paired with a male it laid an additional 293 eggs and the
hatchability of the eggs increased gradually up to the normal level of
65 percent. The oviposition rate remained fairly constant throughout
oviposition period (Table 39).

Field-collected active spring adults that were collected on
April 28, 1966 when a few eggs were observed in the field laid from
40 to 256 eggs per female in an isolated cage in the laboratory.
Considerable individual differences as to fecundity and longevity were
observed among the adults of the same age group. A 95 percent confidence
limit for the mean egg production per female was calculated to be from
163 to 1,099 eggs for the beetles that had been stored for 110 days at
38° F. and from 28 to 225 eggs for the field-collected active spring
adults (Table 40).

The cereal leaf beetle laid a significantly greater number of
eggs at 80° F. than at 85° F. (Table 9). In another test, the survival
of the larvae and pupae at 73° F. and 80° F. was not significantly dif-
ferent (Table 11). The egg laying was extremely poor under fluctuating
day and night temperatures of 70°—50O F. and 75°-65° F. A.maximum egg
production was apparently attained when the temperature was maintained
at 80° F. constantly (Table 12).

The largest egg production was observed under the photoperiodic
range of 16 to 18 hours, when the temperature was maintained at 80° F.

and relative humidity at 75 percent. The rate of oviposition, however,

140
was higher under 18 hours than that under 16 hours of photoperiod
(Tables 14 and 15).

Over 93 percent of the eggs were laid during l6-hour light
period and only 7 percent during 8-hour dark period. Thus oviposition
activity in the cereal leaf beetle seems to be confined only during
day light hours (Table 17). The photoperiod, however, had no influence
on the development of the immature stages (Table 16).

The overwintering adults were more readily reactivated and laid
a significantly greater number of eggs at the high relative humidity
of 95 to 100 percent than at 70 to 80 or 45 to 55 percent (Table 18).
The optimum environmental conditions for the development of the cereal
leaf beetle, therefore, seem to be 80° F., 18 hours of photoperiod, and
95 percent of relative humidity.

The wet soil containing free water seems to have a detrimental
effect on the prepupae entering the soil for pupation. Although a
slightly moist soil seems to favor the general pupation process, a
complete development of the pupae can take place in a completely dry
soil (Tables 19, 20, and 21).

Soil type and color did not seem to affect oviposition behavior
of the female (Table 22). The soil type, however, seems to be an
important factor affecting the pupation process in the cereal leaf
beetle (Table 23). A light, well aerated soil seems to be the best
soil type for the development of the pupae.

A small lamp chimney cage seems to be more effective than a
larger cage in inducing earlier and more consistent egg laying in over-
wintering adults. For active spring adults the egg production was

higher in a larger cage than in a lamp chimney cage (Table 24).

141

"Clintland 60" oats are apparently preferred to "Hudson" barley
for feeding and oviposition by the cereal leaf beetle. The adult
beetles, after 65 days of cooling period at 43° F., consumed an average
of eight 4 l/Z-inch tall oat seedlings and 5.4 barley seedlings per
beetle when they were exposed to either oats or barley during 45-day
test period. During the same period, the same beetles laid 56 eggs
per female on oats and only 22 eggs per female on barley (Table 30).
These figures seem to underestimate the actual figures because diapause
development in this beetle was apparently not completed at the time of
the test.

In another test, when the beetles were exposed to both oats and
barley and were given a choice of host plants, they laid a consistently
greater number of eggs on oats than on barley and the difference was
statistically highly significant (Table 31). The female seems to pre-
fer slightly rough and concaved leaf surface and the leaf width of
about 3 to 4 mm. for oviposition.

A slightly larger number of eggs was deposited on 4-inch tall
seedlings than on 2— or 6-inch tall seedlings and more eggs were found
in a pot with 75 seedlings than in a pot with either 50 or 25 seedlings.
The differences, however, were statistically not significant (Table 32).

In ”Clintland 60" oats over 99 percent of total eggs laid were
deposited on upper surface of the leaves and 68 percent of them were
found on basal third of the leaves. In "Hudson" barley, however, only
62 percent of the eggs were deposited on upper surface and 45 percent
of them were found on basal third of the leaves. Nearly 68 percent of

the eggs occurred singly on the upper surface of the oat leaves and 44

142
percent of the eggs were deposited singly on the same surface of the
barley leaves (Table 49). The cereal leaf beetle laid significantly
greater number of eggs on the upper surface of the leaves in oats re-
gardless of the posture of the leaves (Table 50).

A single spotted lady beetle, Coleomegilla maculata lengi

 

Timberlake, consumed up to 76 cereal leaf beetle eggs in 24—hour period.
A nearly 100 percent egg predation occurred with a pair of lady beetles
in 4 days when the lady beetles were confined in a lamp chimney cage
containing an average of 152 cereal leaf beetle eggs (Table 35).

In the laboratory test, the cereal leaf beetle was able to
complete its development within a temperature range of 58° F. to
90° F. The eggs, larvae, and pupae were unable to complete their
developments at 48° F. (Table 3). The calculated thresholds of develop-
ment, according to Uvarov's (1931) equation, are 52.00 F. for the egg,
46.60 F. for the larva, 54.00 F. for the pupa, and 51.60 F. for the
entire immature stage (Table 7). A complete development of the eggs
occurred at 95° F. but not at 1000 F. The larvae and pupae developed
normally at 90° F. but not at 95° F. The peak temperatures at which
the embryo develops at the fastest rate was 92.5° F. A.more complete
range of temperature for the development seems to be between 54° F.
and 92.5° F.

A complete development from an egg to adult requires an average
of 92 days at 58° F., 52 days at 67° F., 28 days at 80° F., and 23 days
at 90° F. Both Davidson's (1944) logistic and linear regression equa-
tions were used to express the relationship between temperature and

the rate of development in egg, larval, and pupal stages (Table 5).

143

Intra-specific competition among the larvae and adults was
tested in the laboratory. However, no aggressive behavior was observed
among the larvae and adults. At least two 4-inch tall oat seedlings
are required for a larva to complete its development (Table 26). A
decrease in fecundity of the females was observed as the adult density
increased. The egg production was highest in the laboratory stored
beetles at the initial density of 20 adults (10 females) per lamp
chimney cage with 50 fresh seedlings changed every other day. For
field—collected active spring adults, the greatest egg production was
obtained at the lowest density of 10 adults (5 females) per lamp
chimney cage with 30 fresh plants changed every two to four days. The
former (20 adults) laid as high as 330 eggs per female while the latter
(10 adults) laid 213 to 224 eggs per female (Tables 27, 28, and 29).

The egg is the most resistant stage against extremely cold
temperatures of 0° and -10° F. and it is followed by pupae, larvae,
active summer adults, and lastly by active spring adults. A 100
percent egg mortality occurred within 2 hours at -100 F. and in 4 hours
at 0° F. Although diapausing adults have not been tested in the
laboratory, it is most likely that the hibernating adults might be the
most resistant of all stages against the cold since the inactive summer
adults can withstand a considerable period of time at 38° F. At high
temperatures of 1100 F. and 1200 F., inactive summer adults were most
resistant. It is then followed by larvae, eggs, pupae and active
summer adults, and spring adults. A complete kill of the inactive
adults was observed within 6 hours at 1200 F. and in 5 days at 1100 F.

(Table 13).

144

Under normal conditions both in the laboratory and field, the
cereal leaf beetle seems to have an obligatory diapause. under field
conditions it seems to have a single generation per year and all of the
newly emerged summer adults go into diapause after a brief feeding
period (Castro, E£.§lx: 1965). Even in the laboratory, when the newly
emerged summer adults were held in a large screen cage (15-1/2 x 15-1/2
x 16 inches) with hiding places in it, all the adults hid inside the
hiding places after the post-emergence feeding period regardless of
the environmental conditions. When the summer adults were kept in a
small lamp chimney cage, they started laying eggs after varying period
of time. The egg laying is generally irregular and the egg production
is extremely low (Table 45).

The egg laying by the summer adults, however, seems to be in-
fluenced to some extent by 1) age of the beetle after emergence,

2) temperature, 3) photoperiod, and 4) light intensity. The newly
emerged adult seems to be the most responsive stage for a continuous
reproduction. As the summer adults get older the induction of egg
laying becomes harder. Exposures of eggs, larvae, pupae, and new
adults to various combinations of 12, 16, and 24 hours of photoperiods
have failed to prevent the summer adults from going into diapause.

A brief exposure of the summer adults to extremely low tempera-
tures of 0° or -100 F. and to extremely high temperatures of 1100 or
120° F. did not favor the egg production in the summer adults (Table 36).
The number of eggs produced by the summer adults that had been exposed
for 30 days to 330/320/150 F. or 38°/32° F. was not significantly dif-
ferent from that produced by the adults exposed for 30 days to 38° F.

constantly (Table 37).

145

Some of the early eggs laid by the summer adults were sampled
and reared under different photoperiods of 12, 16, and 24 hours for
three successive generations without subjecting them to a cold tempera-
ture. The egg production gradually decreased and no apparent non-
diapausing strain was detectable from the samples (Table 44).

An age-specific life table was constructed for the laboratory
population of the cereal leaf beetle. Starting with an imaginary
number of 1,000 eggs, 301 new adults were obtained and 202 adults sur-
vived after 2 weeks of post-emergence feeding period and 90 days of
cold storage period at 38° F. The 202 adults are comparable to the
spring adults and these are ready to mate and lay eggs of the following
generation. The apparent mortality was highest in the pupal stage
(39.0%) followed by the egg stage (35.2%) and the larval stage (23.9%)
(Table 46).

Based on an age-specific life and fertility table for the beetle
that had been stored at 380 F. for 90 days, the net reproduction rate
was calculated to be 3.936 under the laboratory rearing conditions
(Table 47). Using a similar table for the field-collected spring
adults, applying field mortality data prepared by Dr. R. F. Ruppel
(unpublished data), the net reproduction rate of the field population
was estimated at .941 (Table 48). Assuming all the data on fertility
and survival of the female and mortality of various developmental
stages of the beetle are sufficiently correct, the laboratory popula-
tion can multiply about four times per generation while the field

population remains relatively constant.

LITERATURE CITED
Abbott, W. B. 1925. A method of computing the effectiveness of an
insecticide. J. Econ. Entomol. 18:265-7.

Allee, W. C. 1931. Animal aggregations, a study in general sociology.
Univ. Chicago Press, Chicago. 431 pp.

Andersen, F. S. 1960. Competition in populations consisting of one
age group. Biometrics. 16:19-27.

Andrewartha, H. G. 1952. Diapause in relation to the ecology of
insects. Biol. Rev. 27:50-107.

Andrewartha, H. G. and L. C. Birch. 1954. The distribution and abun-
dance of animals. Univ. of Chicago Press, Chicago. 782 pp.

Averin, V. G. 1914. Review of the pests noticed in the Govt. of
Charkov during 1913. pp. 10-65. (Cited from Hodson, 1929.)

Balachowsky, A. S. 1963. "The family Chrysomelidae". Entomologie
appliquee 3_l'agriculture. Masson et Cia., Paris. Vbl. 2.

 

Balachowsky, A. S. and L. Mesnil. 1935. "Lema melanopa L." Les
insectes nuisibles aux plantes cultivees. Est. Busson, Paris.
pp. 788-95.

 

 

Beck, S. D. and W. Hanec. 1960. Diapause in the European corn borer,
Pyrausta nubilalis (Han.). J. Insect Physiol. 4:304-19.

 

Belehradek, J. 1930. Temperature coefficients in biology. Cambridge
Phil. Soc. Biol. Rev. 5:30—58.

Birch, L. C. 1948. The intrinsic rate of natural increase of an
insect population. J. Anim. Ecol. 17:15-26.

Borg, A. 1959. The grain leaf beetle, a common harmful insect.
vaxtskyddsnotiser. 23(5):63—7. (From an English translation
by M. K. Lien.)

Bowers, W. S. and C. C. Blickenstaff. 1966. Hormonal termination of
diapause in the alfalfa weevil. Science. 154(3757):1673-4.

Castro, T. R. 1964. Natural history of the cereal leaf beetle
Oulema melanopa (Linnaeus) and its behavior under controlled

environmental conditions. Ph.D. thesis, Mich. State Univ.
121 pp.

 

146

147

Castro, T. R. and G. E. Guyer. 1963. Notes on the biology, distribu-
tion, and potential importance of Oulema melanopa (L.) in the
Mid-West. Abst. in Proc. North Central Branch, Entomol. Soc.
Amer. 18:74.

 

Castro, T. R., R. F. Ruppel, and M. S. Gomulinski. 1965. Natural
history of the cereal leaf beetle in Michigan. Mich. Agr.
Expt. Sta., Mich. State Univ. Quart. Bull. 47(4):623-53.

Chapman, R. N. 1928. The quantitative analysis of environmental
factors. Ecology. 9:111-22.

Chiang, H. C. and A. C. Hodson. 1950. An analytical study of popula-
tion growth in Drosophila melanogaster. Ecol. Monogr. 20:
173-206.

 

Connin, R. V., D. L. Cobb, J. C. Arnsman, and M. S. Gomulinski. 1966a.
Laboratory rearing of the cereal leaf beetle, Oulema melanopa (L.).
Entomol. Res. Div., A.R.S., U.S.D.A. Special Rpt. W4222.

 

1966b. Plaster of Paris as an aid in rearing insects
pupating in the soil. J. Econ. Entomol. 59(6):1530.

Connin, R. V., O. K. Jantz, and W. S. Bowers. In press. Termination
of diapause in the cereal leaf beetle. J. Econ. Entomol.

Crombie, A. C. 1942. The effect of crowding upon the oviposition of
grain-infesting insects. J. Exptl. Biol. 19:311-40.

1944. On intraspecific and interspecific competition in
larvae of graminivorous insects. J. Exptl. Biol. 20:135—51.

Crozier, W. J. 1926. On curves of growth, especially in relation to
temperature. J. Gen. Physiol. 10:53-73.

Davidson, J. 1942. On the speed of development of insect eggs at
constant temperatures. Aust. J. Exptl. Biol. & Med. Sci.
20:233-9.

1944. On the relationship between temperature and the
rate of development of insects at constant temperatures.
J. Anim. Ecol. 13:26-38.

DeBach, P. 1958. The role of weather and entomophagous species in the
natural control of insect populations. J. Econ. Entomol.
51:474-84.

Deevey, E. S. 1947. Life tables for natural populations of animals.
Quart. Rev. Biol. 22:283-314.

Dickson, R. C. 1949. Factors governing the induction of diapause in
the oriental fruit moth. Ann. Entomol. Soc. Amer. 42:511-37.

148

Ditman, L. P., G. S. Weiland, and J. H. Guill. 1940. The metabolism
in the corn earworm. III. Weight, water, and diapause.
J. Econ. Entomol. 33(2):282—95.

Embree, D. G. 1965. The population dynamics of the winter moth in
Nova Scotia, 1954-1962. Mem. Ent. Soc. Can. 46. 57 pp.

Favinger, J. J. 1962. A new insect pest: cereal leaf beetle, Oulema
melanopa (L.). Outdoor Indiana. 6(5):2-4.

Finney, D. J. 1947. Probit analysis, a statistical treatment of the
sigmoid response curve. Cambridge Univ. Press.

Fry, F. E. 1947. Effects of the environment on animal activity.
Univ. Toronto Stud. Biol. 55:1-62.

Gallun, R. L. and R. F. Ruppel. 1963. Cereal leaf beetle resistance
studies. Agr. Res. Serv., U.S.D.A. Special Rpt. W4178, 36 pp.

Grison, P. 1947. Developpement sans diapause des chenilles de
Euproctis phaeorrhaea, L. (Lep. Liparides). Compt. rend. Acad.
Sci., Paris. 225:1089-90. (Cited from Wigglesworth, 1953).

 

Guyer, G. E. 1962. The bionomics of Oulema melanopa (L.) on small
grains in Michigan. Abst. in Bull. Entomol. Soc. Amer. 8(3):162.

 

Harvey, W. R. 1962. Metabolic aspects of insect diapause. Ann. Rev.
Entomol. 7:57-80.

Hodson, W. E. H. 1929. The bionomics of Lema melanopa L. (Criocerinae)
in Great Britain. Bull. Ent. Res. 20(1):5-14.

 

Hoopingarner, R. A., S. Kumararaj, and A. L. French. 1965. Gametogenesis
and radiation effects in the cereal leaf beetle, Oulema melanopa.
Ann. Entomol. Soc. Amer. 58(6):777-81.

 

Hoskins, W. M. and R. Craig. 1935. Recent progress in insect
physiology. Physiol. Rev. 15:525-96.

Huffaker, C. B. 1944. The temperature relations of the immature
stages of the malarial mosquito, Anopheles quadrimaculatus,
with a comparison of a developmental power of constant and
variable temperatures in insect metabolism. Ann. Ent. Soc.
Amer. 37:1-27.

James, R. L. and R. F. Ruppel. 1965. Cereal leaf beetle control.
Mich. State Univ. Ext. Bull. 443. 4 pp.

Janisch, E. 1932. The influence of temperature on the life history
of insects. Trans. Roy. Ent. Soc. London. 80:137-68.

149

Kadocsa, G. 1916. Criocerus melanopa (Lema melanopa) injurious to
oats and barley in Hungary. Mthly. Bull. Agr. Intel. Dis.
7(2):312—4. (Abst. in Rev. Appl. Entomol. 4:350.)

 

Kadocsa, J. Undated. The red-necked barley beetle, its life history
and control. (From an English translation by G. Angelet.)

Kevan, D. K. M. 1944. The bionomics of the neotropical cornstalk
borer, Diatraea lineolata Wlk. (Lep. Pyral.) in Trinidad.
Bull. Ent. Res. 35:23.

 

Klomp, H. 1964. Intraspecific competition and the regulation of
insect numbers. Ann. Rev. Entomol. 9:17-40.

Knechtel, W. K. and C. I. Manolache. 1936. Biological observations
on_L. melanopa in Rumania. Anal. Inst. Cerc. Agron. Roman.
7:186-208. (Abst. in Rev. Appl. Entomol. 24:678.)

Kogure, M. 1933. The influence of light and temperature on certain
characters of the silkworm, Bombyx mori. J. Dept. Agr. Kyushu
Imp. Univ. 4:1-93.

 

Kumararaj, S. 1964. Gametogenesis and radiation effects on the
reproductive tissue of Oulema melanopa (L.). M.S. Thesis.
Mich. State Univ. 77 pp.

 

Laughlin, R. 1965. Capacity for increase: a useful population
statistic. J. Anim. Ecol. 34:77-91.

Lees, A. D. 1955. The physiology of diapause in arthropods. Cambridge
Uhiv. Press, Cambridge. 151 pp.

Manolache, C. 1932. On the occurrence 0f.£: melanopa in Rumania in
1931. Pub. Soc. Nat. Romania, 10. 4 pp. (Abst. in Rev.
Appl. Entomol. 20:340.)

Matteson, J. W. and G. C. Decker. 1965. Development of the European
corn borer at controlled constant and variable temperatures.
J. Econ. Entomol. 58:344-49.

McLagan, D. S. 1932. The effect of population density upon the rate
of reproduction with special reference to insects. Proc. Roy.
Soc. London, B. 111:437-54.

Megalov, V. A. 1925. Report of the work of the Entomological Division
for 1920-1925. Saratov Reg. Agr. Expt. Sta. 31 pp. (Abst.
in Rev. Appl. Entomol. 14:29.)

1927. Lema melanopa L., a pest of oats, barley, and other
graminaceous plants. Ibid. 29 pp. (Abst. in Rev. Appl.
Entomol. 15:643.)

 

150

Mesnil, L. 1931. Contribution a'l'etude de trois coleopteres nusibles
aux cereales. Ann. Epiphyties. l6(3-4):190-208. (Abst. in
Rev. Appl. Entomol. 19:658.)

Merino M., L. G. 1966. Studies of the sexual behavior of the adult
cereal leaf beetle, Oulema melanopus (L.). M.S. Thesis,
Mich. State Univ. 25 pp.

 

Messenger, P. S. and N. E. Flitters. 1958. Effect of constant
temperature environments on the egg stage of three species of
Hawaiian fruit flies. Ann. Entomol. Soc. Amer. 51:109-19.

Morris, R. F. 1963. The dynamics of epidemic spruce budworm popula-
tions. Mem. Ent. Soc. Can. 31. 332 pp.

Mbrris, R. F. and C. A. Miller. 1954. The development of life tables
for the spruce budworm. Can. J. Zool. 32:283-301.

Park, T. 1932. Studies in population physiology: The relation of
numbers to initial population growth in the flower beetle,
Tribolium confusum Cuval. Ecology. 13:172-81.

 

1933. Studies in population physiology. II. Factors
regulating initial growth of Tribolium confusum populations.
J. Exptl. Zool. 65:17-42.

 

Pearl, R. and S. L. Parker. 1922. On the influence of density of
population upon the rate of reproduction in Drosophila.
Proc. Nat. Acad. Sci. 8:212—19.

 

Pearl, R. and L. J. Reed. 1920. On the rate of growth of the
population of the United States since 1790 and its mathematical
representation. Proc. Nat. Acad. Sci., Washington. 6:275-88.

Robertson, F. W. and J. H. Sang. 1944. The ecological determinants
of population growth in Drosophila cultures. I. Fecundity
of adult flies. Proc. Roy. Soc. London, B. 132:258-77.

Ruppel, R. F. 1964. Biology of the cereal leaf beetle. Proc. North
Central Branch, Entomol. Soc. Amer. 19:122—4.

Ruppel, R. F. and T. R. Castro. 1964. Cereal leaf beetle; life cycle,
biology and damage. Abst. in 16th Illinois Custom Spray Oper.
Training School. Urbana, Illinois. pp. 46-7.

Ruppel, R. F., David L. Cobb, and Melvin S. Gomulinski. 1965. Control
of cereal leaf beetle pupae. Mich. Agr. Expt. Sta., Mich.
State Univ. Quart. Bull. 47(3):328—3l.

Sang, J. H. 1949. The ecological determinants of population growth
in a Drosophila cultures. III. Larval and pupal survival.
Physiol. Zool. 22:183—202.

 

151

Sengupta, G. C. and B. K. Behura. 1957. On the biology of Lema
praeusta Fab. J. Econ. Entomol. 50(4):471-4.

Shade, R. E. and M. C. Wilson. 1964. Population build-up of the
cereal leaf beetle, Oulema melanopa (L.), in Indiana and the
apparent influence of wind on dispersion. Agr. Expt. Sta.,
Purdue Univ. Res. Prog. Rpt. 98.

 

Shelford, V. E. 1929. Laboratory and field ecology. Williams and
Wilkins Co., Baltimore. 608 pp.

Smith, H. S. 1935. The role of biotic factors in the determination
of population densities. J. Econ. Entomol. 28:873-98.

Southwood, T. R. E. 1966. Ecological methods with particular refer-
ence to the study of insect populations. Methuen and Co.,
Ltd., London. 277-310.

Squire, F. A. 1940. On the nature and origin of the diapause in
Platyedra gossypiella, Saund. Bull. Ent. Res. 31:1—6.

 

Urquijo, P. 1940. Una plaga de Lema melanopa entrigos de Galicia.
301. Pat. Veg. Ent. Agr. 9:147-163.

 

U. S. Department of Agriculture. 1958. A leaf beetle (Lema melanopa

 

L.) in "Insects not known to occur in the United States."
Coop. Econ. Insect Rept. 8(3):47-8.

. 1962. Survey reports on cereal leaf beetle. Ibid.
12(32):881.

. 1963. Coop. Plant Pest Cont. Programs, Fiscal Year 1963.
Plant Pest Cont. Div., A.R.S., U.S.D.A. pp. 8-9.

1964. Coop. Plant Pest Cont. Programs, Fiscal Year 1964.
ibid. pp. 9-10.

1965. Coop. Plant Pest Cont. Programs, Fiscal Year 1965.
ibid. p. 7.

1966a. Coop. Plant Pest Cont. Programs, Fiscal Year 1966.
ibid. p. 8.

1966b. Coop. Programs, Central Region, Fiscal Year 1966.
ibid. pp. 7-14.

1967. Coop. Econ. Insect Rpt. ibid. l7(31):720.

Utida, S. 1941. Studies on experimental population of the Azuki
bean weevil, Callosobruchus chinensis (L.). IV. Analysis of
density effect with respect to fecundity and fertility of
eggs. Mem. Coll. Agr. Kyoto Univ. 51:1-26.

 

152

. 1942. Studies on experimental population of the Azuki
bean weevil, Callosobruchus chinensis (L.). VII. Analysis of
the density effect in the preimaginal stage. Mem. Coll. Agr.
Kyoto Univ. 53:19-31.

 

uvarov, B. P. 1931. Insects and climate. Trans. Roy. Entomol. Soc.
London. 79:1-248.

Vassiliev, E. V. 1913. The chief remedies against the larvae and
beetles of Lema melanopa L., a pest of summer grown grain.
Studies from Expt. Sta. All-Russian Soc. Sugar-Ref. 1912, Kiev.
pp. 1-2. (Abst. in Rev. Appl. Entomol. 1:479.)

 

Venturi, F. 1942. La Lema melanopa L. (Coleoptera, Chrysomelidae).
Redia. 22:11—86.

 

Vereshtchagin, B. 1914. Experiments on the control of Lema melanopa
L. in Bassarabia. Agr. Bassarabia. 19. 4 pp. (Abst. in Rev.
Appl. Entomol. 4:218.)

 

Way, M. J. and B. A. Hopkins. 1950. The influence of photoperiod and
temperature on the induction of diapause in Diataraxia oleracea
L. (Lepidoptera). J. Exptl. Biol. 27:365—6.

 

Wigglesworth, V. B. 1953. The principles of insect physiology.
Methuen and Co. Ltd., London. 546 pp.

Wilde, J. de. 1962. Photoperiodism in insects and mites. Ann. Rev.
Entomol. 7:1-26.

Wilde, J. de and J. A. de Boer. 1961. Physiology of diapause in the
adult Colorado beetle II. Diapause as a case of pseudo-
allatectomy. J. Insect Physiol. 6:152-61.

Wilde, J. de, G. S. Duintjer, and L. Mook. 1959. Physiology of
diapause in the adult Colorado beetle. I. The photoperiod as
a controlling factor. J. Insect Physiol. 3:75—85.

Williams, C. M. 1956. Physiology of insect diapause. X. An endocrine
mechanism for the influence of temperature on the diapausing
pupa of the cecropia silkworm. Biol. Bull. 110:201-18.

Wilson, M. C. and R. F. Ruppel. 1964. Airplane trapping of the
cereal leaf beetle and the meadow spittlebug. Agr. Expt. Sta.,
Purdue Univ. Res. Prog. Rpt. 110. 7 pp.

Wilson, M. C. and R. E. Shade. 1964a. Adult feeding, egg deposition
and survival of larvae of the cereal leaf beetle on seedling
grains. Agr. Expt. Sta., Purdue Univ. Res. Prog. Rpt. 97.

7 pp.

153

. 1964b. The influence of various gramineae on weight gains
of post-diapause adults of the cereal leaf beetle, Oulema
melanopa (Coleoptera: Chrysomelidae). Ann. Entomol. Soc. Amer.
57(6):659-61.

1966. Survival and development of the cereal leaf beetle,
Oulema melanopa (Coleoptera: Chrysomelidae), on various species
of Gramineae. Ann. Entomol. Soc. Amer. 59(1):170-3.

Wilson, M. C. and H. Toba. 1963. Cereal leaf beetle. Coop. Econ.
Insect Rpt. 13(33):942.

Yun, Y. M. 1964. Laboratory and field studies of insecticides for
control of the cereal leaf beetle. M.S. Thesis. Mich. State
Uhiv. 76 pp.

Yun, Y. M. and R. F. Ruppel. 1964. Toxicity of insecticides to a
coccinellid predator of the cereal leaf beetle. J. Econ.
Entomol. 57(6):835-7.

Zolotarev, E. K. 1947. Diapause and development of puape of the
Chinese oak silkworm (Antheraea pernyi Guer.). Zool. Zhur.
26:539. (Cited from Lees, 1955.)