'r

‘L
I};
5}

”I

C‘.
{5"
‘{
I
l

'1‘
I
I_IHJ*
'- l
. .'
1%Q.‘[
. u ~
L'n.,..'
I. I. I

#IF‘”7

I"
V'Lf Q:

._"T

n.1,“?! '

I 4. din. .
.fltafivwga . 1.
fight» .. I ..

In. .‘I. ctvrb .l .

t.7 F“... I

.tmlthufl‘H-

U

l
I

v
ll.
9!)

’9.

l
I

7?”
I

v: :
o. . nu i...{¢
Av .|~.~‘ 99‘ .
.. «Hitskzv
‘ t . ‘v ‘ I
5... 4n. thaw”; um...»
u v.
. . . 30.1.“)...2... In

.4 .flv. 4:31.?41

‘QUI. 0- ‘i “u.

I ¢ I a n .. .
. ‘ .Q ‘ V 1
(1 U :. I .
u. .l I :- 0. 1 ¢ I
V .u‘Vfi—i {”0‘Olllo Icn.< I.

In! ‘ 11....A: Lyn-00.:f9 I n{
' 004‘»? cot. l... vv.<.-u00.1¢...00u
o . v. $4 .ll.vlfr..’A3Iv9)1-:u..rhv a
. .- 10 1.0 I
p o 1.9 s 11.. . 51011:...ILD). f9p\1§.al.<l£oo|l’ or”... vs
.. .I : ... v ., ‘0”..1 00“. -.¢_l.-AFv-’V’.ot In...
‘4 I a , I .l. A "'. . I III‘ I
.7." . .. . I _ .4I.. u, n , ‘ a . Llohdunn‘l o 34301...th
. , . . I. r. VI. in...
. I. y 4 . .. . I _. . .. A I . . I on...
n . .I. . I” «1.1- A.‘ . 1..)th

, LN.rA1I. . . .

v1 LEAH!“ -

O .
a. I!!! q .
..\ Hun... av. .-
.IoIn.ul.II- .
!!.4.:‘l‘I-.. ..
u . .7 . o .
AOHIFflio-l o- .VR...\ ~ .
A - 71...... . c n.
u I v n u
‘ I. .14 . . A. c , . .N.
1: c.- .. . .. c .
‘ ' ' U ‘
19.1.." Yfibvvvo»11l\.0£| w .-
: '"fl‘."..“ 5“.”5'“ I § 9‘
I‘Voflfil “fl. 3.! v
'0. . ‘90“ Vigil. I‘V‘OI 00!:701‘
$0.1m- . 5.1! . ‘II..NVV4..'~II\.
. c “Vokoo . .rv fl... V. 001!
I... 9ft! 3 u u
2 q.
x

3

. u .-
. .053". I n
.
. H-.:a.,..r$MII .
u a 10‘ I. 0"! §
v).,\ua '30.. .outdx purl-ix vs.
QUV‘iI‘c‘v‘éfific r”: .ulvr . he flfl'fl‘
L.J’lfl ‘t‘o M! . . n
a o 14 o
I o

SCI
. 4;;
o n n u

2.?

H

M

n
D‘.
V!
1
Ivan

ID!
.
pl-
I
v.4.
i:

n
.-

I)! ’5‘.- .
O N .
ll n¢vtbti
ons Q.
.4 \mA.
." fl

 

 

V t
v u
0 v ‘1 t
.. .O’n
0.00 c kvzjunfi.1¢i‘n.
....' 1"... ‘ II 9. .- v.1 ll‘.t
t . . . , I . . .I II .4 1
I li‘hl'r I .- I'r I III: Illa.”

MICHIGAN STATE UNIVERSITY 8
H
I

I!l”‘ll“”“’illll'I”

 

 

 

 

 

III I III

3 1293 00558 3921

LIBRARY
Michigan State
University

 

If m " ‘ mm

 

 

 

 

 

 

 

 

 

This is to certify that the

dissertation entitled

BEHAVIOR AND FIELD DYNAMICS OF THE POTATO
LEAFHOPPER (EMPOASCA FABAE (HARRIS)):
THE INFLUENCE OF TOMATO AND BEAN
INTERCROPPING.

presentedby
WILLIAM JAMES ROLTSCH

has been accepted towards fulfillment
of the requirements for

Ph . D . degree inENTOMOLOGY

 

S III/H any

 

Major professor
STUART H. GAGE

Date BK“ AZ /759

 

MS U is an Waive Action/Equal Opportunity Institution 0-12771

 

 

MSU

LIBRARIES
-;—.

 

 

RETURNING MATERIALS:
Place in book drop to
remove this checkout from
your record. FINES will
be charged if book is
returned after the date
stamped below.

 

 

"0010 a 40 non

 

 

BEHAVIOR AND FIELD DYNAIICS OF THE POTATO

LEAFHOPPER (Euzgasga EABAE (HARRIS)):
THE INFLUENCE OF rouaro AND BEAN
INTERCROPPING.

BY

WILLIAH JAIES ROLTSCH

A DISSERTATION

Sub-ttted to
Itchtgan State Unlverslty
tn partial fulfill-ant ot the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Depart-ant of Ento-ology

1988

:3 /’/ ch 0%

ABSTRACT
BEHAVIOR AND FIELD DYNAIICS OF THE POTATO
LEAFHOPPER, (Eureasca EABAE (HARRIS)):
THE INFLUENCE OF BEAN AND TOMATO
INTERCROPPING
BY

WILLIAI JAMES ROLTSCH

Intercropping is considered to be an agricultural
practice which can reduce insect pest damage to food crops.
Lower pest densities in intercrops versus monocultures have
been commonly Observed, but few studies have attempted to
quantify the mechanism behind such differences. This study
investigated the population dynamics Of the potato leafhop-
per (PLH). amneasca iibi: (Harris), on its bean host plant
in monoculture and on bean intercropped with tomato.

Studies Of this system were conducted under field and
laboratory conditions. Field studies investigated PLH
abundance in relation to companion plant (tomato) density,
host plant (bean) canopy density, and host plant quality.
Laboratory studies quantified leafhopper movement, feeding
and oviposition on bean with the inclusion Of various
companion plant leaves.

PLH egg and nymph field densities on bean foliage were
significantly different between treatments, being inversely
related to tomato density. Based upon the similarity in PLH
egg and nymphal density patterns throughout the field

season, the analysis showed that lower levels of oviposition

on bean interplanted with tomato were responsible for
treatment differences. Adults did not respond to differ-
ences in bean canopy density, however they did responded
positively to bean quality, defined by total foliar nitro-
gen. In laboratory studies, PLH feeding was reduced 43% in
the presence Of tomato. Feeding on bean was reduced because
PLH resided extensively on tomato, yet fed very little on
it. In oviposition choice tests there were significantly
(P<0.05) fewer eggs laid on bean in treatments including
tomato or cabbage. PLH arrestment and frequency of
movement within the Observation cages were not markedly
changed in the presence of bean with tomato leaves versus
the bean leaf control. However, an overall pattern of
increased movement frequency did occur with the inclusion Of
leaves of other companion plants.

Results support a dual hypothesis regarding the basis
for lower PLH densities on bean and tomato intercrops. PLH
utilization Of bean, including feeding and oviposition, is
directly reduced by tomato, and changes in host plant (bean)

quality resulting from bean/tomato interactions.

ACKNOWLEDGMENTS

I wish to extend my sincere thanks to: my advisor, Dr.
Stuart H. Gage for his support and patience during the
course of this project; and my thesis committee members,
Drs. Thomas Edens, Alan Putnam, Gene Safir, and Mark Vhalon
for their helpful suggestions regarding my research, and
thesis review. I also which to thank Dr. James Bath, former
departmental chairperson, for his interest and support of my
research and assistantship.

Thanks is also given to Mr. Gregory Anderson for his
many diligent hours of field and laboratory assistance, as
well as to Mr. Jose Velarde for his help in maintaining the
field site at the Kellogg Biological Station, through thick
and thin.

A very special thanks is given for the love, support,
and patience Of my wife, Irene; and encouragement by my
parents, William H. and Amy J. Roltsch, and sisters and
their families.

PREFACE

This study began because of an interest in alternate
approaches to agricultural pest management. The premise was
that insect herbivores were more likely to be maintained at
acceptable levels if certain plant assemblages were selected
to foster appropriate community interactions. Background
knowledge of insect life histories, and information on the
potential influence of non-host vegetation on herbivores
were necessary to initiate research in this area. Except in
a few isolated situations, such information was unavailable,
particularly that relevant over large geographic areas. The
potato leafhopper, bean, and tomato system was selected
based upon information obtained through a screening process
of several plant combinations. Results indicated that
tomato was responsible for reduced numbers of potato
leafhoppers on bean interplanted with tomato.

All field studies were conducted at the Kellogg
Biological Station, near Hickory Corners, Michigan.
Laboratory studies were conducted on the Michigan State
University campus.

This dissertation is presented in manuscript form. A
general introduction discusses issues of ecosystem divers-
ification, the role of intercropping in pest control, and
chemical ecology of Solanaceous plants. It is followed by a
manuscript reviewing the life history and phylogeny of the
potato leafhopper. Two subsequent manuscripts pertain to

field and laboratory investigations of the potato leafhopper
v

within the context of intercropping. All manuscripts are
written in accordance with the journal guidelines of the

Entomological Society of America.

w

TABLE OF CONTENTS

LIST OF TABLES
LIST OF FIGURES

INTRODUCTION

MANUSCRIPT I. A review of the leafhopper species

EMEQASQA_EABAE (Harris) (Homoptera: Cicadellidae),
with respect to its biology, and phylogenetic and
taxonomic standing

Introduction

The biology of the genus Empgasga
The Biology of W tam

MANUSCRIPT 11. Influence of bean/tomato intercrop-
ping on population dynamics of the potato leaf-
hopper, annasca tibia (Homoptera: Cicadellidae)

Abstract
Introduction
Methods
Results
Discussion

MANUSCRIPT III. Potato leafhopper, Empgaaga fabae
(Homoptera: Cicadellidae), movement, oviposition
and feeding response patterns in relation to host
and non-host vegetation.
Abstract

Introduction

Materials and methods

V“

Page
IX

XI

15
24

28

45
47
52
63

81

90
91

94

Results

Discussion

CONCLUSIONS

BIBLIOGRAPHY

APPENDICES

A. Potato leafhopper field study

B. Potato leafhopper behavior study

wn

105

117

124

128

141

156

LIST OF TABLES
Page
MANUSCRIPT I

Table 1. A list and evolutionary ranking of 19
the generally recognized subfamilies
of Cicadellidae (based on Nielson 1985).

MANUSCRIPT II

Table 1. ANOVA tables for potato leafhopper . 67
nymph densities versus tomato density.
Data are presented for 1985 and 1986
field studies over successive julian
dates.

Table 2. Insect and spider predators on bean and 71
tomato plants sampled throughout 1985
in bean monoculture and four intercrop
treatments representing different den-
sities of tomato interplanted with bean.

Table 3. Mean adult potato leafhopper counts per 76
20 plants in bean plots representing
three different canopy densities.

Table 4. Greenhouse study of potato leafhopper 78
oviposition in relation to bean plant
total nitrogen; conducted as four
separate trials.

Table 5. Average bean and tomato yields in 1985 79
and 1986 studies consisting of a bean
monoculture and four intercrop treat-
ments representing different densities
of tomato intercropped with bean.

MANUSCRIPT III

Table 1. Species, variety and size of plants 98
used in experiments.

a

Table 2.

Table 3.

APPENDIX A
Table 1.

Table 2.

APPENDIX B

Table 1.

Table 2.

Average time leafhoppers spent on
leaves, and excreta production
(droplets) over 12 h, in small cages
containing two bean or tomato leaves,
or one bean and one tomato leaf.

Potato leafhopper oviposition choice
tests. Paired comparisons represented:
bean with companion plants compared to
a bean control.

Data from 1985 intercrop field study.
Data from 1986 intercrop field study.

Mean number of minutes a leafhopper
spent on each plant surface during
the 15 min. small cage, observation
study. A treatment contained two
leaves.

Mean number of minutes during an arrest-
ment bout on bean leaves, for those
treatments containing bean (i.e. bean
controls, and bean/companion-leaf treat-
ments). A treatment contained two leaves.

111

115

148

153

157

143

LIST OF FIGURES

INTRODUCTION

Fig.

MANUSCRIPT

Fig.

Fig.

Fig.

Fig.

Fig.

1c

1.

3.

An organizational diagram of the
research program components involved
in the study of the direct influence
of tomato and other non-host plants
upon the potato leafhopper (PLH), as
well as effects of variables created
through intercropping.

II

Plot diagram of apple orchard inter-
planted with tomato and bean in 1983.
Treatments were blocked within two
locations of the orchard. The treat-
ments were: bean monoculture, bean/-
tomato dicultures with two different
tomato densities "D 1” and ”D 2", and
tomato monoculture with two within row
spacings.

Bean and tomato intercropped in plots
forming increasing densities of tomato
over the length of each of four blocks.
Rows of bean are represented by stars,
and circles identify tomato plants.

Mean number of potato leafhopper nymphs
per three trifoliate bean sample in 1983
bean/tomato intercrop study.

Number of potato leafhopper nymphs per ma
bean leaf area on monoculture and tomato
diculture plots in 1985.

Number of potato leafhopper nymphs per

three trifoliate bean sample on monocul-
ture and tomato diculture plots in 1986.

xi

Page

11

53

55

64

66

Fig. 6.

Fig. 7.

Fig. 8.

MANUSCRIPT
Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Graphical analysis of the relationships

between bean, tomato and PLH nymph density
within the bean/tomato intercrop during
julian date 205, 1986. 1) nymph density
by tomato treatment, 2) bean plant leaf
area by tomato treatment, and 3) nymph
density by mean plant leaf area. Units of
measurement are: tomato plants per row
meter, nymph density per 3 trifoliate
sample, and leaf area (m’) per bean plant.

Mean number of eggs per potted bean plant
per week, in each treatment within the
intercrop study during 1985.

Mean adult potato leafhopper densities
per .3 ma soil surface in two alfalfa
strips. Sample SEM is (20% for each date.

III

A small cage for conducting PLH
observation studies in the presence
of leaves positioned at each end.

A cage with sticky, vinyl panels for
monitoring PLH residency on selected
plant environments.

Mean time spent on leaf surfaces during
15 min exposure, in observation cages
containing either two bean leaves, two
companion leaves, or one bean and one
companion leaf. Bars with same letters
are not significantly different in total
height (P<0.0S; Waller-Duncan preceded
by rank transformation and one-way ANOVA;
[F=5.0; df=l3,227; P<0.05]).

Mean number of surface to surface (leaf

1, leaf 2, or cage) transitions during 15
min, in observation cages containing
either two bean leaves, two companion
leaves, or one bean and one companion
leaf. Bars with same letter are not
significantly different (P<0.0$; Waller-
Duncan preceded by a one-way ANOVA (F22.9;
df=13,238; P<0.05]).

xfi

69

73

74

95

100

106

107

Fig. 5. Leafhoppers remaining on plant treat- 113
ments within cages containing bean,
tomato, or bean and tomato plants.
Fifteen female leafhoppers were released
into each cage and their rate of capture
on the sides of the cage was monitored
for 48 hr.

APPENDIX A

Fig. 1. Number of potato leafhopper nymphs per 141
bean plant in monoculture and tomato
diculture plots in 1985.

Fig. 2. Graphical analysis of 1985 intercrop, 142
E, fabae nymph populations and bean
plant growth by replicate over succes-
ive dates. 1) nymph density by tomato
treatment, 2) bean plant leaf area by
tomato treatment, and 3) nymph density
by bean plant leaf area. Units of
measurement are: tomato plants per row
meter, nymph density per leaf area (m’);
leaf area (m’) per bean plant.

Fig. 3. Graphical analysis of 1986 intercrop, 145
a, fang: nymph populations and bean
plant growth by replicate over successive
dates. 1) nymph density by tomato treat-
ment, 2) bean plant leaf area by tomato
treatment, and 3) nymph density by bean
plant leaf area. Units of measurement
are: tomato plants per row meter, nymph
density per 3 trifoliate sample, leaf
area (m’) per bean plant.

APPENDIX B

Fig. 1. Mean duration of an arrestment bout 156
on bean leaves among the bean controls
and diculture treatments. Differences
between treatments were not significant
(P<0.05; rank transformation and one-way
ANOVA; IF=0.4; df=7,136; P<0.051).

xfii

INTRODUCTION

The theory that stability of plant and animal communi—
ties is a direct function of species diversity was consid-
ered dogma for many years in ecology (Risch 1980). It was
believed that as a result of food web interactions across
trophic levels, natural ecosystems were less likely to
fluctuate radically (a measure of stability) with progres-
sive increases in habitat diversity (MacArthur 1955, Graham
1956, Elton 1958). Investigations of predator/prey rela-
tionships and reports by foresters that pure, even-aged tree
stands.were subject to more insect outbreaks than their
diverse counterparts, were used to support the theory
(Huffaker 1958, Chumakova 1960, Gibson and Jones 1977). In
addition, consideration of the theory extended into agricul-
ture. It was believed that stability could be brought about
within agriculture systems through unspecified diversifica-
tion (Pimental 1961, Pimental et a1. 1963, van Emden 1965).

When the theory of "ecosystem diversity and stability"
was more closely evaluated, a lack of correspondence between
diversity and stability was noted (watt 1965, van Emden and
Williams 1974, May 1976). That is, it has been determined
that progressive increases in diversity do not necessarily
insure greater stability. Furthermore, there are two main

problems with the concept as it related to agriculture

(Risch 1980). First, it is of little importance that
populations are stable if densities are high enough to cause
economic damage. Secondly, the collection of evidence from
agriculture, comparisons between natural systems, laboratory
studies, and mathematical models, simply does not indicate
that species richness per se provides increased stability.
This is not to say that diversity is unimportant. There are
many examples in the area of biological control demonstrat-
ing significant reductions in pest abundance fostered by the
presence of various plant and animal species within a
habitat (De Bach 1964, Huffaker 1971, Huffaker and Messenger
1976, Tanigoshi 1983). However, the results are due to
specific interactions requiring specific system components.
In essence, the theory of stability being a direct function
of the degree of diversity, missed its mark by emphasizing
the number of interactions rather than the significance of
those interactions.

Studies of the influence of intercropping on herbivore
and natural enemy communities may provide important insights
into understanding the factors responsible for pest out-
breaks and the specific kinds of plant diversification that
may facilitate pest control. Intercropping (mixed-cropping)
involves the simultaneous growth of multiple crops or wild
plants in the same field (Perrin and Phillips 1978). The
different kinds of intercropping are: mixed intercropping
(plants are not in rows), row intercropping (one or more

crops planted in rows), strip intercropping (alternate

3

multiple row patterns), and relay intercropping (second crop
planted when the first crop approaches maturity). In part,
intercropping research has been pursued because it provides
a format for utilizing potentially important ecological
interactions for pest control. However, to date the most
clear advantage in intercropping lies in reducing the risk
of crop failure, particularly in subsistence farming (Kass
1978, Horwith 1985). Its potential value in modern mechan-
ized agriculture and as a means of controlling insect pests
has also been discussed (Risch et a1. 1983, Horwith 1985).
These authors believe that with significant changes in
mechanization, intercropping can be a viable alternative in
developed countries. Furthermore, it was noted that based
on a survey of pest abundance in 150 intercropping studies;
53% of the insect pests were less abundant in the inter-
crop, 188 were more numerous in the intercrop, 9% showed no
difference, and 20% showed a variable response (Risch et a1.
1983).

The basis for comparative research of intercropping
systems versus their monoculture counterparts has been
linked to several hypotheses (Root 1973, 1975). The
”enemies hypothesis" predicts that herbivore populations can
be better controlled in species-rich plant associations due
to greater numbers of natural enemies. The reasons for this
are related to the improved spatial and temporal distribu-
tion of multiple food resources for natural enemies includ—

ing pollen, nectar, and alternate hosts. Regarding the

4

importance of natural enemies, it has been argued (Price et
a1. 1980), that predators and parasites should be more
important in perennial than annual systems. This is because
their hosts are more predictable (more easily found) in
space and time. Also, perennial plants commonly produce
chemical defense substances which act in a quantitative
fashion, reducing herbivore growth rates in contrast to
killing them outright (Feeny 1976, Rhodes and Cates 1976).
Therefore, plant survival against herbivores in perennial
systems would appear to be contingent upon the. joint
presence of host plant defense chemistry and natural
enemies. In contrast, annual plant species are less likely
to be found in the same location over time, and produce
substances which kill all but a few co-evolved phytophagous
species. These phytophagous species have circumvented their
host plants defenses, and in some cases sequester plant
substances to ward off attack by natural enemies (Price et
a1. 1980). The belief that natural enemies demonstrate
higher rates of establishment in perennial systems has been
supported by empirical evidence (Clausen 1978, Hall and
Ehler 1979, Hall et a1. 1980). However, the viewpoint that
predators and parasites have little potential in annual
systems may be a misconception. As pointed out by Risch
(1983), this may be a function of wrongly applying perennial
crop biological control theory to annual crop pest problems.

It has been recently suggested that natural enemies that are

generalists with high dispersal ability may be more effec-
tive control agents in annual cropping systems than special-
ists (Ehler 1979, Newsom et a1. 1980).

In contrast to the "enemies hypothesis”, the "resource
concentration hypothesis" predicts that herbivores
maintain higher population densities in resource—dense areas
because the concentrated resources are easier to locate, and
more importantly, if the resource is particularly suitable
they will stay longer (Root 1973, 1975). Overall, it is
expected that in pure stands of host plant species, herbi-
vores will have a higher rate of accumulation, tenure, and
reproductive success. Other authors have elaborated on this
hypothesis by stating that colonization is affected by
visual and chemical stimuli from host and non-host plants,
and that this is related to the absolute density and spatial
arrangement of host and companion plants (Bach 1980, Risch
1983, Risch et a1. 1983). Furthermore, these authors
mention that pest survivorship may be increased in monocul-
ture systems as a function of resource concentration. Risch
et al. (1983) also point out that for annual cropping
systems, the resource concentration hypothesis can better
explain reductions in pest loads in intercrop systems than
the enemies hypothesis.

Few studies have investigated in detail, the dynamics of
pest populations in intercropping systems versus monocul-
tures. Therefore, mechanisms responsible for observed

differences have been identified for only a few systems.

6

The importance of growth form in colonization was indicated
when vertically grown cucumber plants had greater densities
of the chrysomelid beetle, Acalymma yitata, (Fab.), than
horizontally grown plants (Bach 1981). Shade has been
determined to play an important role in influencing insect
densities as well. Studies on a chrysomelid complex
attacking plants in typical Central American intercrops
(squash, maize, and bean), determined that shade produced by
corn, directly influenced colonization by some beetle
species (Risch 1980, 1981). The capability of a companion
plant to directly influence the herbivore of the associated

plant species is evident. Upon evaluating the effects of

tomato, Lyggpgrsicgn esgnlgntnm Mill, on the diamond back
moth, Elnifilli xxlflfitfilli. (L.), tomato appeared to be
directly responsible for reducing pest densities on cabbage
intercropped between rows of tomato (Buranday and Raros
1975). In that study, there were 50% fewer eggs found on
cabbage intercropped with tomato during sample dates
occurring 25 days or later following the transplanting of
crops into the field. Also, there was no indication, based
on yield data, that cabbage growth, size or quality was
altered by tomato and thereby accounting for the observed
differences in pest densities. In another study where
tomato and bean were intercropped, apgdgptgza,snnia Guenee,
a lepidopterous pest of both crops, had little impact on

tomato (the primary production plant) when intercropped with

bean(Rosset et al. 1985, 19871 In that system, bean acted as

a trap crop because of its greater acceptability by the
pest. These studies are cited because they are among the
few intercropping studies that have provided evidence of a
basis for the observed differences between treatments. In
the majority of intercropping studies, the qualitative state
of host plants has not been considered (Bach 1981, 1984).
Depending on the system, insect populations have been
observed to increase or decrease when their host plants are
stressed by low water or low or high nitrogen availability
(Rhoades 1983, Scriber 1984).

With continued developments in the area of insect/plant
interactions, in which chemical ecology is of major import-
ance, greater insights into the potential utility of
intercropping will be obtained. Some plant groups are known
to have extensive mechanical and chemical defense systems
used against other plant species, pathogens, and herbivores.
One of the most extensively studied plant families exhibit-
ing such characteristics is the family Solanaceae (D'Arcy
1986). Despite there being few insect species attacking
wild solanaceous plants, many cultivated species exist which
frequently sustain considerable damage by insects and plant
pathogens. Defenses within this family commonly include
those which are mechanical and chemical. Mechanical
defenses include prickles, trichomes, and glands, while
chemical defenses include alkaloids , saponins, essential

oils, etc. (Drummond 1986).

8

The family Solanaceae is particularly well known as a
group with rich alkaloid plant chemistry (Harborne 1986).
Levin (1976) found that alkaloids are most broadly found in
the family Solanaceae (Hsiao 1986). Of those species
included in a survey, 85 % of the solanaceous species have
alkaloids. There are principally three groups of alkaloids
found in this plant family: 1) steroidal, 2) tropane, and 3)
pyrrolidine alkaloids. Although alkaloids are frequently
associated with host plant defence, blanket generalizations
regarding their presence can not be made, for their effects
are relatively specific (Robinson 1979).

Species from which domestic tomato and potato, Solanmm
tnbergsnm L., were derived have extensive chemical defense
systems. Their secondary plant chemistry would seem to make
them (especially tomato) a potentially good choice for
intercropping from a pest protection standpoint. Wild
species of figlannm contain the alkaloid demissine, which is
believed to be an important resistance factor, defending
many Sglannm species against the Colorado potato beetle. In
contrast, solanine, the primary alkaloid in domestic potato,
is very similar in structure to demissine. However, it has
little influence on the Colorado potato beetle, thereby
exemplifying the specific role of alkaloids in host plant
defence (Harborne 1986). Tomatine, a major alkaloid in
tomato, has been demonstrated to be a strong repellent to
the Colorado potato beetle (Harborne 1986). Resistance of

tomato to the Colorado potato beetle has been found to be

correlated with tomatine content, which varies across
varieties. This appears to be a clear example of how plant
resistance can be lost during the development of new
cultivars (Sinden et. al. 1978). Tomatoes have many other
groups of compounds and mechanical defenses that may also be
responsible for conferring resistance. Several phenolic
compounds in tomato (i.e., chloragenic acid and rutin, a
flavonol glycoside) are growth inhibitors of the tomato
fruitworm, ugligthis zen, (Boddie), (Elliger et a1. 1981;
Isman and Duffey 1982ab). The ketohydrocarbon, 2-tridec-
anone has been isolated from the trichomes of tomato. It is
toxic to the tomato hornworm, Mandnga, quinqnemacnlata
(Haworth), tomato fruitworm and an aphid species (Kennedy
and Yamamoto 1979, Williams et al. 1980). However, domestic

tomato has far lower concentrations than its wild ancestor,

W Wm f. glabratnm 0.8. Mull. The tobacco
flea beetle, Enltllx.hllilnfinn1§.(Melsheimer), has also been

found to be deterred by the presence of chemicals located
within wild tomato leaves (Gentile and Stoner 1968). In add-
ition, a number of insect species are trapped by a sticky

substance produced by the trichomes of various Lyggpgrsiggn
and figlannm, species. The plant species used for study were
typically L; 011:9: m Humb. and Bonpl., and a. berthanltii

Hawkes. The insect species affected include the greenhouse

white fly. Wm (Vestwood), Wm
cinnabarinus (Boisduval), two spotted mite, 1L urtigag Koch,

10

and the green peach aphid, Myzns persigae (Sulzer), (Gentile
et al. 1968, 1969, and Tingey and Laubengayer 1981).

The study of insect population dynamics within
intercropping systems is in its early phase of development.
It is obvious that plants in such systems may have very
complex secondary chemistry, mechanical defenses and growth
forms, capable of significantly altering herbivore densities
in contrast to their monoculture counterparts. Many factors
play into evaluating the role of pest abundance in inter-
crops versus their monoculture counterparts and past
observations have been insufficient to clearly identify the
general significance of intercropping as a means of modify-
ing the density of pest species.

The subject matter of this dissertation pertains to
insect/plant interactions within the context of an intercrop
system. The primary motivation for pursuing this topic was
an interest in developing ecologically based approaches to
pest management. The overall study plan is presented in
Fig. 1. To achieve a state of reduced reliance upon
conventional pesticide control, one means of diminishing
insect outbreaks on crops would be through the specific
IDENTIFICATION of a multi-plant species SYSTEM. Such a
system would be expected to provide a basis for supporting
an insect/plant community capable of a higher degree of
self-regulation compared to its monoculture counterparts.
In 1983, in the pursuit of a potentially important insect/-

intercrop interaction, an INTERCROPPING DESIGN of bean and

11

 

SYSTEM
IDENTIFICATION

 

   

 

  
 

  
   

  

FIELD DESIGN
FOR SCREENING

l

PLH POP. DENSITIES
V IN RELATION TO
TOMATO PLANT DENSITY

   

 

 

FIELD
STUDIES

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I EVALUATION I
COMPANION pLANT
' Eflflfifllflfl=
NYpOTNEsEs DIRECT ,
~ EFFECTS PLH
l MOVEMENT
DESIGN
OF FIELD AND LABORATORY PLH
LAD. EXPERIMENTS STUDIES OVIPOSITION
FOR STUDYING » ,
INTERCROPPING PLH
EFFECTS ON PLH FEEDING
EFFECT OF DEAN PLANT
CANOPY DENSITY
FIELD
STUDIES
DEAN QUALITY
INDIRECT EASURED As YIELD
EFFECTS D LEAF AREA
LABORATORY
STUDIES
, DEAN QUALITY
MEASURED As TOTAL
ITROOEN

 

Fig. 1. An organizational diagram of the research program
components involved in the study of the direct influence of
tomato and other non-host plants upon the potato leafhopper
(PLH), as well as effects of variables created through
intercropping.

12

tomato within a newly planted apple orchard was developed.
Tomato was selected due to its history of insect/plant
interactions. Bean was selected because of its common use
in intercropping, and compatibility with tomato. Apple
represented a perennial, and therefore a persistent, long-
term feature to the cropping environment, providing perman-
ent refugia for natural enemies. From this first phase of
study, results showed that the potato leafhopper on snap
bean obtained higher population densities in plots where
bean was planted alone, versus with tomato (Fig.3 in
Manuscript 11). Based upon that finding, it was hypothe—
sized that, (1) as a companion plant, tomato directly
influenced potato leafhopper abundance on bean, and (2) the
influence would be linearly related to the density of
tomato, up to some high density (saturation level) of
tomato. To investigate these hypotheses, laboratory and
field studies were designed and conducted (Fig.1). Field
research was directed toward quantifying the differences in
leafhopper nymph densities and oviposition on snap bean in
the presence of tomato, and to provide evidence that could
be used with results from laboratory studies to determine
the mechanism. This included experiments that were con-
ducted to determine the importance of the confounding
variables of variable bean plant growth and plant quality,
which differed in correspondence with tomato density.

Laboratory studies evaluated specific leafhopper behavioral

responses to been in the presence of non-host plants, and to

13

bean representing several qualitative states, based upon the
restriction of nutrients. The responses evaluated included
residency time on bean, movement frequency, feeding, and
oviposition. Overall, evidence was sought to determine
whether tomato directly or indirectly influenced the potato
leafhopper. The terms DIRECT and INDIRECT EFFECTS were used
for purposes of organization, to delineate between different
groups of effects. Direct effects were those which could be
immediately traced back to tomato without considering the
host plant. This included tomato plant chemistry, natural
enemies, and micro-climate effects. Indirect effects were
those effects of tomato mediated through changes in the bean
host plant, which in turn influenced PLH. These included
host plant quality and quantity.

The following manuscripts represent a review of the
life history and phylogeny of the potato leafhopper, and an
analysis of the interaction between this economically
important insect pest, noted for its complex life history
and wide host range, and a well accepted host-plant (snap
bean) interplanted with a non-host (tomato). These studies
represent an approach to investigating a complex pest in a
complex agro-ecosystem to obtain a mechanistic view of how
the insect might be manipulated in a multi-cropping environ-

ment.

MANUSCRIPT I

A REVIEW OF THE LEAFROPPER SPECIES EIEQASQA_EAEAE (HARRIS),
(HOIOPTERA: CICADELLIDAE), WITH RESPECT TO ITS BIOLOGY, AND
PRYLOGENETIC AND TAXONONIC STANDING

14

15

INTRODUCTION

This introduction to Empgagga flange (Harris) is
presented from a taxonomic, phylogenetic and life history
perspective. Although reviews have been written on the
general biology of leafhoppers (DeLong 1971, Knight 1983,
Nault and Rodriques 1985), reviews Of taxonomic groups
within this family are uncommon. A great deal of leafhopper
taxonomy remains to be done and is under constant revision,
thereby making it difficult to track pertinent literature.
This is particularly true for the genus Empaazna, since it
represents a very large, cosmopolitan insect genus. Despite
the fact that the list of described species in the western
hemisphere, and throughout the world, has grown extensively,
Delong's (1931a) key to the genus Empgasga in America north
of Mexico remains the single most comprehensive key avail-
able for this genus (Southern 1982). Southern (1982) noted
that nearly 460 nominal species have been assigned to the
genus in the Western Hemisphere alone, and more than 85
species have been recorded from South America. Beirne's
(1956) publication is very useful for identifying many
leafhopper taxa in the northern United States and Canada.
However, it is of limited use for identifying species of
Empgasca, A number of fine publications on the biology and
phylogeny of Empgasga_ are available, including a bibli-
ography of E, fahae (Gyrisco et al. 1978). The overview

16

presented herein should be of particular value to those
reviewing the literature pertaining to E. flange, and will
hopefully encourage efforts in developing comprehensive sum-
maries of other extensively studied members of this family.

Leafhoppers, family Cicadellidae, are differentiated
from related families by the presence of one or more rows of
small spines extending the length of the hind tibia. There
are approximately 2500 species in North America alone, and
they are typically less than 13 mm in length (DeLong et al.
1931). worldwide, it is estimated that about '10,000
leafhopper species have been described, with nearly again
that many yet to be described (Viraktamath 1983). This
would seem to be a conservative estimate since Nielson
(1985) estimates that there are 4,000 genera represented by
15,000 described species, and upwards of 30,000 species yet
to be described. Much of the fauna in the tropics and
southern continents is unknown.

The classification of Cicadellidae has not reached the
stage of development that is comparable with many other
groups of insects, such as Coleoptera or Lepidoptera.
Development of systematics in the group was slow because
leafhoppers were not considered important until the early
part of 20th century. At that time they were first recog-
nized as injurious to crop plants, and important vectors of
plant pathogens (Nielson 1985).

In the family Cicadellidae, the male genitalia are used

as the primary character to identify and classify nearly all

17

species and most genera. In females, characters of similar
value are almost completely lacking. The structure of the
aedeagus among leafhopper species varies from a simple,
symmetrical tube-like structure to an asymmetrical organ of
diverse form.

Despite the usefulness Of the male genitalia for
species identification, Nielson (1985) points out that
closely related sympatric species that are difficult to
differentiate by aedeagal morphology or by other morpholog-
ical means are common in the Cicadellidae. For example,
several taxa in the genera Circuliger, ,garnegggphala, and
Macrgstglgs have similar aedeagal types but are biologically
distinct species. In some instances aedeagal morphology has
been noted to vary within a species. For example, a
correlation between day length and morphometrics of the
aedeagus within the same species in the genus Ensgglis was
noted by Muller (1957). As discussed later, in the case of
Empggsga, flange, the inclusion of apodemal structures in
addition to characteristics of the genitalia used in
identifying members of the Emnnaana.fahi: complex, has been
instrumental in shaping the current understanding of the
distribution and phylogeny of E. faba: (Ross and Moore
1957). As a result, what was once considered to be Empgasca
Lana: in collections from North and Latin America actually
represented an entire complex of species that could be
reliably differentiated by apodemes of the basal abdominal
tergites.

18

Currently, there is still no consensus of the number of
subfamilies of Cicadellidae. Nielson (1985) notes that
Evans(1966), Ross(1957), Wagner(1951), and Linnavouri(l959)
have grouped the various subfamilies into taxonomic divi-
sions: Typhlocybides, Iassides, Cicadellides, Eurymelides,
Xerophloeides, Macropsides, and Tartessides. The subfamil-
ies and their evolutionary standing is presented in Table 1.
The relationship among many subfamilies of leafhoppers is
not continuous, suggesting that the gaps between them are
represented either by undiscovered or extinct species.

Most Of the subfamilies considered phylogenetically
primitive occupy Australia and the adjacent Indo-Malayan
land bridge, while the more advanced subfamilies, Delto-
cephalinae and Typhlocybinae, are cosmopolitan (Nielson
1985). As the subfamily Typhlocybinae is presently consti—
tuted, its members are remarkably uniform morphologically
compared to Deltocephalinae, which presently exhibits wide
variation in size and external features. Speciation in both
groups has been extensive; each has a large number of taxa
and together have more species than the remaining subfamil-
ies combined. As indicated by their wide ranges, each
possesses a high degree of plasticity and adaptability to a
broad range of host plants in all zoogeographical regions
(Nielson 1985).

Relationships between certain taxa and their biotic and
abiotic environments are becoming evident. Most leafhopper

species are restricted to a single generation per year. All

19

Table l. A list and evolutionary ranking of the generally
recognized subfamilies Of Cicadellidae (based on Nielson 1985).

 

SUBPAMILIES EVOLUTIONARY RANKING

 

EURYMELINAE

AUSTROGALLOIDIINAE Most primitive
EUACANTHELLINAE (originated in Australia
MYERSLOPIINAE or New Zealand)
STENOCOTINAE

POGONOSCOPINAE

THAMMATOSCOPINAE

XEROPHLOEINAE Primitive
ULOPINAE

STEGELYTRINAE

MEGOPHTHALMINAE

KRISNINAE

HYLICINAE

AGALLIINAE

MACROPSINAE

LEDRINAE

TARTESSINAE Intermediate
COELIDIINAE
CICADELLINAE
NIRVANINAE
GYPONINAE
IASSINAE
IDIOCERINAE
EVACANTHINAE
PHEREURHININAE
DRABESCINAE
MAKILIGIINAE

CEPHALELINAE Advanced
PENTHIMIINAE
HECALINAE
XESTOCEPHALINAE
APHRODINAE
DORYCEPHALINAE
NEOCOELIDIINAE
NIONIINAE
MILBEHANINAE
BYTHONIINAE
NEOBALINAE

TYPHLOCYBINAE Most Advanced
DELTOCEPHALINAE

 

20

species in the family Cicadellidae, and for that matter in
the order Homoptera, are phytophagous (DeLong et. al.
1981). Generally, the host plant range of most leathpper
species is very limited, which dictates the existence of a
relatively well defined habitat associated with each
species. For example, species Of the subfamily Idiocerinae
occurring in the nearctic region, breed on willows and
poplars. Members of the tribes Balcluthini and Deltoceph-
alini of the subfamily Deltocephalinae, feed and propagate
almost entirely on Graminaceae (Nielson 1985). Knight's
(1983) review of leafhoppers of Southeast Asia Pacific area
gave an account of the host plants known for a number of
subfamilies. Most members of the Ulopinae usually occupy
the base of plants or roots and are slow moving. Members of
the subfamily Euacanthellinae live in marshes. The Macrop-
sinae are mostly arboreal and have a restricted host plant
range. All of the Tartessinae in Australia occur on
xerophytic trees and shrubs; those in New Guinea on forest
trees and shrubs.

Relative to the total number of leafhopper species, few
are pests, and it is estimated that less than 1% of the
described species are recognized as pests, either as a
direct result of feeding or the transmission of a disease.
They are commonly known for their ability to carry and
transmit phytopathogenic diseases, including viruses,
mycoplasmas, spiroplasmas, and bacteria (Nielson 1985, Nault

1985). Compared to aphids, which are strictly phloem

21

feeders, leafhoppers are known to exploit the phloem, xylem,
mesophyll, or all three tissues in some cases (Backus 1985).

At present there are 151 vector species in 65 genera
assigned to eight subfamilies. The subfamilies Cicadellinae
and Deltocephalinae comprise most of the vector species.
Over 60% of the vector genera and species belong to Delto-
cephalinae, and they transmit over 70% of the known patho-
gens (Nielson 1985). It should be noted that these two
groups are among the most phylogenetically advanced groups
of leafhoppers. In the subfamily Cicadellinae the high
propensity for disease transmission may be a direct function
of feeding characteristics and the associated body struc-
tures. All species are restricted to feeding in the plant
xylem. This is made possible by the presence of a highly
developed, musculated clypeus allowing for sap to be
withdrawn from the xylem. This structure is a major
taxonomic feature of this group. Furthermore, it should be
pointed out that the xylem is an ideal site for the propaga-
tion of many plant diseases (Nielson 1985).

The subfamily Typhlocybinae, within which the genus
Empgasga exists, represents the second largest subfamily of
Cicadellidae (Knight 1983). In North America there are over
700 species, of which over 300 belong to the genus Erythro-
neura (DeLong et a1. 1981). As pointed out by Nielson
(1985), subfamily designation of leafhopper groups has been
important for separating major groups, and justified since

the gaps separating the subfamilies of leafhoppers are

22

relatively narrow compared to the separation of family
groups in other taxa such as Fulgoroidea.

Characteristics used to differentiate members in Typhlo-
cybinae from other subfamilies pertain to the absence of
cross veins in the wings except for those in the apical
portion, and indistinct veins in the basal area (Beirne
1956). In addition, they are small, fragile, macropterous
insects, and the ocelli are often absent. Member species
are primarily arboreal although many species are associated
with herbaceous plants (Knight 1983). Members of this
subfamily are predominately mesophyll feeders, as exempli-
fied by all species in the tribe Erythroneurini. Yet the
tribe Empoascini is predominately comprised of phloem
feeders (Vidano and Arzone 1983). Feeding traits are
variable even within a genus. For example, in the genus
Empoasga, EL tape: is a well known phloem tissue feeder
while E, abrupt: is a mesophyll feeder.

Although members in the family Cicadellidae most
commonly have only one generation per year, Vidano and
Arzone (1983) note that species of Typhlocybinae in the
temperate zones typically have three generations. Only four
species in the subfamily Typhlocybinae are known vectors of
plant pathogens (Nielson 1985). Empgasga,deyastans Distant
(currently Amlififii. dexaatans (Distant), Ghuari 1983),

transmits a disease termed "little leaf of brinjal” in S.E.
Asia (Knight 1983). Sohi (1983) noted that Empgagga papaya:

Oman was a vector of bunchy top virus of papaya in Puerto

23

Rico, and Alsbmldss. We (Distant) (formerly A.
draxidanu1) was a vector of purple top and witch's broom

disease of potato.

Detailed surveys of past taxonomic studies of the
subfamily Typhlocybinae are presented by Ahmed (1983) and
Sohi (1983). Worldwide, the subfamily Typhlocybinae
contains six tribes: Alebrini, Dikraneurini, Erythroneurini,
Typhlocybini, Empoascini and Zyginellini. Following Young's
(1952) description of Typhlocybini which included the genus
Ennnasca, Mahood and Ahmed (1968) erected the tribe Empo-
ascini, to which the genus Emnniina was then transferred.
The tribe Zyginellini was erected by Dworakowska (1979).
However, Ahmed disputed the validity of separating the
genera from Typhlocybini and their placement in Zyginellini.
Prior to the creation of the tribe EmnnaSSIDIJ Beirne (1956)
distinguished Typhlocybini from other tribes in the
subfamily Typhlocybinae by the presence of vein IV in the
hind wing and characteristics of the submarginal vein in the
hind wing. He also noted that compared to representatives
in the tribe Erythroneurini, they are not usually strongly
marked nor brightly colored.

24

BIOLOGY or THE GENUS Elzggsga

Ross et al. (1964) stated that there were six to seven
hundred species of leafhoppers worldwide that belong to the
genus Empoasga, New World species are represented by 20 to
30 species complexes for which those in the temperate
regions appear to have their origin from ancestors in the
tropics. Delong (1931a) notes that the genus Emnndaca.can
be distinguished from allied genera by the absence of an
appendix in the forewings and the presence of one apical
cell in the hind wing which is closed by a submarginal vein.
Beirne (1956) differentiated the genus from the other
Typhlocybini genera that he addressed by noting the presence
of a submarginal vein at the apex of the hind wing. The
taxonomic characteristics for Emnadana are well illustrated
by DeLong (1931a) and Ross (1959). DeLong (1931a) recogn-
ized four subgenera in his revision of North American
species of Empoasga; Kybos, Hebata, Empoasca, and Idona.
The primary character for differentiating among groups
pertained to the shape of the head's vertex.

Although the potato leafhopper is the predominant
species of Empoasga_attacking crops in the North Central and
North Eastern United States and Canada, DeLong (1938)
pointed out that other species of Empoasga_could be readily
confused with a. flange on wild plant species and apple.
Until DeLong's (1931b) clarification of the apple leafhopper

fauna (including E, flange and E. maligna (welsh)), there

25

existed a great deal of confusion in the literature with
regard to species composition on apple. In the southwestern
and western United States various truck and field crops are
more commonly attacked by species of Empgafigg, adapted to
arid environments and only to a limited extent by E. fighag.
For the most part these species included, E. filamenta.DeL.,
E. axing DeL. and E. ahznnna DeL. DeLong (1938) discussed
regional variation in Emnniina species composition in the
western United States. In addition to these species, E.
gglana DeL. has an extensive range throughout the tropics,
subtropics, southern United States and extending up the
Mississippi river valley. In California since 1952, it has
been recognized as a pest of cotton and more recently bean
and sugar beet (Moffitt and Reynolds 1972).

While some species of Emngasga.are highly adapted to
temperate regions, others such as E. fang; and E. gglana
DeLong are members of species complexes containing repre-
sentatives having more recently adapted to the temperate
zones. As a result they demonstrate what is considered to
be a less evolved state, exemplified by limitations in over-
wintering over the full extent of their annual range (Ross
et a1. 1964).

The Emnnafica, complex is based upon the finding that
specimens previously collected in North and Latin America,
that were consider to be E. fauna, actually represented a
number of species that were remarkably similar in general

morphology and even in terms of the characteristics of the

26

male genitalia used to identify E. Lana: (Ross and Moore
1957, Ross 1959, Ross et a1. 1964). Upon close examination
of these collections it was observed that the apodemes of
the 1st and 2nd abdominal sternites, and 3rd tergite were
distinctly different among certain members of the collec-
tion. In fact they could be easily separated into groups,
with very few intermediate forms present. Relative to other
Empgagga, species, the presence of well developed apodemal
structures in this region of the body is unique to the
Emnniana.complex. By 1964 twenty six species were recognized
in this complex. Overall, as Ross and Moore (1957) pointed
out, member species of the fahae complex could be described
as ranging in body length from 3.5 to 4 mm, having a pale
green color (when alive), whitish markings on head and
thorax, male genitalia with simple aedeagus, hook of tenth
segment with a slender sclerotized ventral point and an
enlarged base, style with only a few short lateral setae and
with tip oblique.

Interestingly, E. Eanag represents the only nearctic
species in the complex, whereby its distribution is limited
to temperate, North America. The remaining species distri-
bution is predominantly in the tropics and subtropics of
South and Central America. Ross (1959) stated that it
appears that the tang: complex is of tropical origin and
that most of its evolution is based on ancestors living in
that zone. Because of the trans-Caribbean distribution of

some of the species, Ross (1959) felt that speciation was

27

based upon the dispersal of vagrants as opposed to disrup-
tive climatic changes over portions of the range of an
ancestral species. However, in a fascinating account of
species origins, Ross (1964) hypothesized that E. Lang;
could be traced back to an E. mgXiLQ-like ancestor having
evolved into a species whose range extended well into North
America. It is then believed that a portion of the
northern population became isolated by an extensive arid
zone and speciation restricted to a temperate climate
occurred, i.e., E. fauna. It should be noted that the
current known distribution of E. mgxa;n_ is in Central

America (particularly Mexico).

28

THE BIOLOGY OF EIEQASQA.EABAE

The potato leafhopper, Emnnafifla. iabae Harris, is a pest of
numerous crop plants, particularly potato, alfalfa, soybeans
and field beans. Its host plant range is well over 100
plant species (P003 and Wheeler 1943, 1949). Empgafiga_fap§§
does not overwinter within North-Central and Eastern United
States (Poos 1932). It is only known to over-winter along
the coast of the Gulf of Mexico and migrates with the
southerly prevailing winds into the North-Central and North
Eastern United States and Canada in late May or early June,
depending on weather conditions (Medler 1957, Pienkowski and
Medler 1964). The first arriving adults are primarily
fertile females (DeLong 1938, 1971). In field and lab
studies Decker et al. (1971) determined the sex ratios of
established populations to be 1:1. Although it was thought
that the North American range of E. Lana: was limited to
areas east of the Rocky Mountains, DeLong (1938) noted that
populations did exist in California. As pointed out by Ross
(1964), in contrast to the eastern population, migrations
associated with the western population have not been
reported. Furthermore, some degree of reproductive incom-
patibility was apparent between those collected in Cali-
fornia and in the Eastern United States.

It was believed that potato leafhopper populations died
in their northern range each year, never to return South.

However, southward migratory flights have been detected from

29

June to September during intermittent periods during which
the winds are from the north-northeast (Taylor and Reling
1986). The prevailing winds during that time of year are
from the west.

Adult longevity is highly variable. In a three year
study DeLong (1938) noted that adults commonly survived
upwards of 30 days in greenhouse conditions and occasionally
they lived as long as 92 days. It can be closely estimated
from Hogg's (1985) data, that for treatments representing
fluctuating diurnal temperature ranges (l3-24° C, 18-29° C,
and 23-34° C), 50% survivorship was 200, 90 and 40 days
respectively. When calculated on a degree-day (DD) basis as
opposed to calender time, convergence of 50% survivorship
among the temperature treatments did not occur.

The majority of oviposition occurs between 2000 and
2400 hr, and it is enhanced by a lengthened photoperiod
(Kieckhefer and Medler 1964). DeLong (1938) estimated that
the average preoviposition period was 6.4 days, and the
average number of eggs laid per female per day was 2.7,
ranging from 2.1 to approximately 6, depending on summer
temperatures in Ohio. The incubation period during mid-
summer was approximately 10 days. In that study females
frequently produced as many as 200 nymphs. Decker et al.
(1971) also estimated oviposition rates to be 2.7 eggs per
day per female. In Decker's study, fecundity ranged between
34 and 57 eggs per female, and it was noted that by trans-

ferring females with an aspirator, oviposition was affected

3O

negatively for upwards of four hours. From data presented by
Hogg (1985), the oviposition rate from low to high temper-
ature treatments was estimated to be .8, 1.2, and 1.6 eggs
per day respectively during the first 600 DD. On a degree—
day scale the rate of oviposition up to 600 DD was nearly
identical among temperature regimes. Hogg's data were of
particular interest since Kieckhefer and Medler (1964)
demonstrated a significant reduction in the rate of oviposi-
tion with relatively small changes in constant ambient
temperature around an optimal temperature of 23.5° C. No
nymphs emerged from plants tested at 15° C and 31.5° C. It
would appear that constant diurnal temperatures artificially
varied oviposition rates as compared to the more realistic
fluctuating temperatures in Hogg's (1985) study. From Hogg
(1985), mean natality for individuals living to the upper
age limit in the low to high temperature treatments was
estimated to be 132, 102 and 82 eggs per female respective-
ly. Simonet and Pienkowski (1980) determined that the lower
and upper thresholds for egg development were 7.6 and 29° C
respectively. Hogg (1985) demonstrated that under fluctuat-
ing diurnal temperatures, the potato leafhopper can develop
well, even with temperatures periodically reaching 34° C.
Adult activity appears to be greater in the evening.
Dysart (1962) determined that 50% of a days flight activity
occurred 30 min. after sunset. Eighty—five percent of those
caught were males. It appears that certain life history

events in relation to movement are unique to each sex.

31

Adler (1982) determined that large populations of E. figggg,
prevalent at dusk on Pennsylvania roads and adjacent soil
surfaces, were 99% males. In terms of leafhopper distri-
bution characteristics within fields, populations have been
noted to aggregate at field margins and within elevated
areas (Kieckhefer and Medler 1965).

The potato leafhopper has five nymphal stadia. The
minimum and maximum developmental time from egg hatch to
adult ranged from 8 to 25 days in generations occurring
throughout the growing season over three years (DeLong
1938). Time spent in each stadia was nearly equal for the
first four stadia and nearly double in the fifth (DeLong
1938, Simonet et al. 1978). Simonet and Pienkowski (1980)
determined that the lower and upper developmental thresholds
for nymphal development is 8.8° C and 29° C respectively.
However, as in the case of egg development, Hogg's (1985)
study refutes the upper threshold value.

P003 and Wheeler (1943, 1949) conducted an extensive
evaluation of E. fang: host plant range. The diversity of
host plants was staggering; including deciduous trees such
as Maples (Ace; spp.), Oaks (Ouercus spp.), Sumac (Shun
spp.), and cherry (Eznnng spp.), to herbaceous annuals such
as Pigweed (Amaranthus Spp.), sugar beet (Egg; ynlgagig L.),
and Dahlia (Dahlia, spp.). P003 and Wheeler (1943) state
that oak and hickory were of special significance as
principal hosts when E. 1321: migrates northward at the

beginning of the season along the Atlantic Coastal Plain.

32

The extent that potential host plants are utilized (based on
lab studies) in nature is variable. Lamp et al. (1984a)
demonstrated that leafhopper development can occur on
pigweed under laboratory conditions, yet none were found on
pigweed in and around alfalfa fields harboring extensive
populations of leafhopper adults and nymphs, which were
found on various other weed host species as well as alfalfa.
Host plant species have a substantial influence on oviposi-
tion and the developmental rates of E. fauna. Kieckhefer
and Medler (1964) determined that E. fanag, has greater
ovipositional acceptance for broadbean over alfalfa, while
both alfalfa and broadbean were more readily accepted than
soybean and field pea. While studying development on four
host plant species, Simmons et al. (1984) determined that E.
fang: developed most rapidly on broadbean and slowest on
soybean. Furthermore, utilization of a plant as a host by
E. fgbag is highly dependent on a host plants phenological
state, and variables associated with host plant distribution
(P003 and Wheeler 1949, Mayse 1978, Lamp et al. 1984, Wells
et a1. 1984).

The potato leafhopper feeds on host plant phloem tissue,
causing damage through the physical destruction of these
tissues and possible introduction of toxins. DeLong (1971)
reviewed the basis of feeding related plant damage. Whether
a toxin is released during feeding is still disputed.
Superficially, potato leafhopper damage results in the

yellowing and stunting of alfalfa, reddening and stunting of

33

clovers, and yellowing, curling, puckering, stunting and
burning of been and potato leaves. For the evaluation of
leafhopper caused damage of beans, Chalfont (1965) presented
a six point rating system using these characteristics.
Hepperburn ratings are correlated with nymphal counts, the
later of which Wolfenberger and Sleesman (1961) believe
should be used as a method for evaluating resistance.
However, leafhopper counts do not always provide an adequate
comparison of resistance between varieties. Eckenrode and
Ditman (1963) showed that while one variety of lime bean was
host to a lower density of potato leafhoppers, its yield was
reduced to a greater extent than were the yields of other
varieties with higher leafhopper densities. Studies
related to the evaluation of potato leafhopper sampling

methods, damage impact and threshold determination are
common (Cherry et al. 1977; Mayse et a1. 1978; Cancelado
and Radcliffe 1979; Simonet and Pienkowski 1979; Wilson et
a1. 1979; Fleischer et al. 1982; Cuperus et al. 1983; Luna
et al. 1983; Flinn and Hower 1984; Walgenbach et al. 1985;
Womack 1984; Walgenbach and Wyman 1984, 1985; Walgenbach
1985; Hower and Flinn 1986). To better assess the complex
interactions between the potato leafhopper and its culti-
vated host plants, several models have been developed
pertaining to potato leafhopper dynamics on alfalfa and
potato (Flinn et a1. 1986, Johnson et al. 1987, Onstad et

a1. 1984, Walgenbach et al. 1985)

34

Literature on host plant defense mechanisms against E.
fang: indicates that trichomes are a major resistance
factor. However, the mechanism through which they operate
is quite different between plant species. In potatoes,
glandular trichomes on wild species encase mouthparts and
tarsi with a viscous exudate that rapidly hardens (Tingey
and Gibson 1978). In soybeans, trichome density apparently
affects nymphal feeding and possibly adult oviposition
(Robbins et al. 1979, Singh et al. 1971, Turnipseed 1977).
In common bean, Ehaagglnz, ynlgaxlg, trichomes are hooked,
and impale leafhoppers. The early instar nymphs are more
greatly affected (Pillemer and Tingey 1976, 1978). Although
resistance in alfalfa has typically been related to the
development of tolerant varieties, trichome secretory glands
condition resistance to potato leafhoppers (Maxwell and
Jennings 1980).

Environmental factors and host plant phenology may be
important in determining the level of host resistance
expressed (McKinney 1938). Pillemerand Tingey (1978) showed
that bean leaves grown in the greenhouse (more shaded) had a
lower density of trichomes and exhibited less of an influ-
ence on E. fang: than did those plants grown in the field.
In potato, it has been found that the phenological stage is
important when leafhoppers are migrating into the field,
such that higher infestations occur on older plants (DeLong
1938, Sanford 1982). Although the cause for this is

unknown, preliminary evidence by DeLong (1938) indicated an

35

association between host plant sugar content and E. £191;
field densities. Additional studies have shown that various
sugars (glucose and lactose) can act as phagostimulants of
E. iahag, while secondary plant compounds in some plants act
to suppress feeding (Dahlman and Hibbs 1967, Dahlman et al.
1981).

In relation to its Close relative, E. kzagmgzi, the
bionomics of the two species appear quite similar (van
Schoonhoven et al. 1985). Several of the most noticeable
differences to date are that E. kzagmgni has anywhere from
four to seven stadia, and the host plant range, although
extensive, does not appear nearly as large as E. fanag's.

In summary, Empgaaga, £523; is a member of a large
successful genus and subfamily of leafhoppers found around

the world. An extensive amount of taxonomic work remains to

be done in the genus Empgagga. Empgagga_£ahag and to a
lesser extent E. Enigmgzi, and E. Eglana represent the few

species of this genus whose biology has been studied in some

detail.

36

REFERENCES CITED

Adler, P.H. 1982. Nocturnal occurrence of leaf hoppers
(Homoptera: Cicadellidae) on soil. J. Kans. Entomol. Soc.
55: 73-74.

Ahmed, M. 1983. Biotaxonomy of Typhlocybine leafhoppers of
Pakistan, pp. 179-187. IN W.J. Knight, N.C. Pant, T.S.
Robertson, & M.R. Wilson [eds.], First international
workshop on leafhoppers and planthoppers of economic
importance. Commonwealth Institute of Entomology, London.

Backus, E.A. 1985. Anatomical and sensory mechanisms of
planthopper and leafhopper feeding behavior. 163-194. IN
L.R. Nault and J.G. Rodriquez [eds.], The leafhoppers and
planthoppers. John Wiley, New York.

Beirne, B.P. 1956. Leafhoppers (Homoptera:Cicadellidae) of
Canada and Alaska. Can. Entomol. 88: 1-180 (suppl. 2).

Cancelado, R.E. & E.B. Radcliffe. 1979. Action thresholds
for potato leafhopper on potatoes in Minnesota. Econ.
Entomol. 72: 566-569.

Chalfont, R.D. 1965. Resistance of bunch bean varieties to
the potato leafhopper, and relationship between resistance
and chemical control. J. Econ. Entomol. 58: 681-682.

Cherry, R.H., K.A. Wood and W.G. Ruesink. 1977. Emergence
trap and sweep net sampling for adults of the potato
leafhopper from alfalfa. J. Econ. Entomol. 70: 279-282.

Cuperus, G.W., E.B. Radcliffe, D.K. Barnes, & G.C. Marten.
1983. Economic injury levels and economic thresholds for
potato leathpper Empoaaca.fabae (Homoptera: Cicadellidae)
on alfalfa uggigggg Ea;1yg_in Minnesota. J. Econ. Entomol.
76: 1341-1349.

Dahlman, D.L. & E.T. Hibbs. 1967. Responses of Empgaggi
tang; (Cicadellidae: Hommoptera) to tomatine, solanine,
leptine I; tomatidine, solanidine, and demissidine. Ann.
Entomol. Soc. Am. 60: 732-740.

37

Dahlman, D.L., L.A. Schroeder, R.H. Tomhave & E.T. Hibbs.

1981. Imbibition and survival response of the potato leaf-
hopper, Empg§§g§_ fauna, to selected sugars in agar media.
Ent. Exp. 5 Appl. 29: 228-233.

Decker, G. C., C.A. Kouskolekas & R.J. Dysart. 1971. Some
observations on fecundity and sex ratios of the potato
leafhopper. J. Econ. Entomol. 64: 1127-1129.

DeLong, D.M. 1931a. A revision of the American species of
Empgagga known to occur north of Mexico. U.S. Dep. Agric.
Tech. Bull. 231: 1-59.

DeLong, D.M. 1931b. The more important species of leafhopper
affecting the apple. J. Econ. Entomol. 24: 1214-1222.

DeLong, D.M. 1938. Biological studies on the leafhopper
Empgaaga fabag as a bean pest. U.S. Dep. Agric. Tech.
Bull. 618: 1-60.

DeLong, D.M. 1971. The bionomics of leahoppers. Annu. Rev.
Entomol. 16: 179-210.

DeLong, D.M., D.J Borror & C.A. Triplehorn. 1981. An
introduction to the study of insects. 5th ed., Science
College, Philadelphia.

Dysart. R.J. 1962. Local movement of the potato leafhopper

in alfalfa. Proc. N. Cent. Br. Entomol. Soc. Am. 17: 100-
101.

Dworakowska, I. 1979. The leafhopper tribe Zyginellini
(Homoptera, Auchenorrhyncha, Cicadellidae, Typhlocybinae).
Revue Zoologie Africaine. 93: 299-331.

Eckenrode, C.J. & L.R. Ditman. 1963. An evaluation of potato

leafhopper damage to lima beans. J. Econ. Entomol. 56:
551-553.

Evans J.W. 1966. The leafhoppers and froghoppers of Aus-
tralia and New Zealand (Homoptera:Cicadelloidea and
Cercopoidea). Aust. Mus. Mem. 12.

Fleischer, S.J., W.A. Allen, J.M. Luna & R.L. Pienkowski.
1982. Absolute density estimation from sweep sampling,
with a comparison of absolute-density sampling techniques
for adult potato leafhopper in alfalfa. J. Econ. Entomol.
75: 425-430.

Flinn, P.W. & A.A. Hower. 1984. Effects Of density, stage,

and sex of the potato leafhopper Empgagga fang: (Homop-
tera: Cicadellidae), on seedling alfalfa growth. Can.
Entomol. 116: 1543-1548.

 

v.3
(ed:
Plan
In3t

Lamp,

IQaf
131.

38

Flinn, P.W., R.A. Taylor & A.A. Hower. 1986. Predictive
model for the population dynamics of potato leafhopper,
Empgaaga_ fang: (Homoptera: Cicadellidae), on alfalfa.
Environ. Entomol. 15: 898-904.

Ghauri, M.S.K. 1983. Scientific name of the Indian Cotton
Jassid. 97-103. IN W.J. Knight, N.C. Pant, T.S. Robertson,
& M.R. Wilson [eds.], First International workshop on
leafhoppers and planthoppers of economic importance.
Commonwealth Institute of Entomology, London.

Gyrisco, G.C. D. Landman, A.C. York, B.J. Irwin & E.J.
Armbrust. 1978. The literature of arthropods associated
with; alfalfa: IV. A bibliography of the potato leathp-
per, Empggfigg £1212 (Harris) (Homoptera:Cicadellidae).
Special Pub. 51, Agric. Expt. Stn., Urbana-Champaign, Ill.

Hogg, D.B. 1985. Potato leafhopper (Homoptera: Cicadellidae)
immature development, life tables, and population dynamics

under fluctuating temperature regimes. Environ. Entomol.
14: 349-355.

Hower, A.A. & P.W. Flinn. 1986. Effects of feeding by potato
leafhopper nymphs (Homoptera:Cicadellidae) on growth and
quality of established stand alfalfa. J. Econ. Entomol.
79: 779-784.

Johnson, K.B., P.S. Teng & E.B. Radcliffe. 1987. Coupling
feeding effects of potato leafhopper, Empgagga, fahag,
(Homoptera: Cicadellidae), Nymphs to a model of potato.
Environ. Entomol. 16: 250-258.

Kieckhefer, R.W. & J.T. Medler. 1964. Some Environmental
factors influencing oviposition by the potato leafhopper,
Empgagga_f§nag. J. Econ. Entomol. 57: 482-484.

Kieckhefer, R.W. & J.T. Medler. 1965. Aggregations of the

potato leafhopper in alfalfa fields in Wisconsin. J. Econ.
Entomol. 59: 180-182.

Knight W.J. 1983. The Cicadellidae of S.E. Asia-present
Knowledge and obstacles to identification, pp. 197-224. IN
W.J. Knight, N.C. Pant, T.S. Robertson, & M.R. Wilson
[eds.), First international workshop on leafhoppers and
planthoppers of economic importance. Commonwealth
Institute of Entomology, London.

Lamp, W.O., M.J. Morris & E J. Armbrust. 1984. Suitability
of common weed species as host plants for the potato

leafhopper, Emngggga_ޤngg. Entomol. Exp. Appl. 36: 125-
131.

39

Lamp, W.O., R.J. Baryney, E.J. Armbrust & G. Kapusta. 1984.

Selective weed control in spring-planted alfalfa: effect
on leafhoppers and planthoppers (Homoptera: Auchenor-
rhyncha), with emphasis on potato leafhopper. Envir.
Entomol. 13: 207-213.

Linnavouri, R. 1959. Revision of the Neotropical Delto-
cephalinae and some related subfamilies (Homoptera). Ann.
2001. Soc. Vanamo 20: 1-370.

Luna, J.M., S.J. Fleischer & W.A. Allen. 1983. Development
and validation of sequential sampling plans for potato
leafhopper (Homoptera: Cicadellidae) in alfalfa. Environ.
Entomol. 12: 1690-1694.

Maxwell, F.G. & P.R. Jennings (eds.). 1980. Breeding plants
resistant to insects. John Wiley, New York.

Mahmood, S.E. & M. Ahmed 1968. Problems of higher Class-
ification of world Typhlocybinae (Cicadellidae:Homoptera).
Univ. Stud. 5: 72-79.

Mayse M.A. 1978. Effects of spacing between rows on soybean
arthropod populations. J. Appl. 15: 439-450.

Mayse M.A., P.W. Price a M. Kogan. 1978. Sampling methods
for arthropod colonization studies in soybean. Can.
Entomol. 110: 265—274.

McKinney, K.B. 1938. Physical characteristics on the foliage
of beans and tomatoes that tend to control some small
insects pests. J. Econ. Entomol. 31: 630-631.

Medler, J.T. 1957. Migration Of the potato leafhopper: a
report on a cooperative study. J. Econ. Entomol. 50: 493-
497.

Moffitt, M.R. & H.T. Reynolds. 1972. Bionomics of Empgfiggg
aglana DeLong on cotton in southern California. Hilgardia
41: 247-298.

Muller, H.G. 1957. Die wirkung exogener faktoren auf die
zylische formenbildung der insekten, insbesondere der
gattung Engggllg (Homoptera: Auchenorrhyncha). Zool.
Jahrb. Abt. System. 85: 317-430.

Nault, L.R. & J.G. Rodriquez (eds.) 1985. The leafhoppers
and planthoppers. John Wiley, New York.

Nielson, M.W. 1985. Leafhopper Systematics, pp. 11-39. IN
L.R. Nault and J.G. Rodriquez (eds.), The leafhoppers and
planthoppers. John Wiley, New York.

PC

40

Onstad, D.W., C.A. Shoemaker & B.C. Hansen. 1984. Management

of potato leafhopper, Empgagga,£§hag (Homoptera: Cicadell-
idae), on alfalfa with the aid of systems analysis.
Environ. Entomol. 13: 1046-1058.

Pienkowski, R.L. & J.T. Medler. 1964. Synoptic weather
conditions associated with long-range movement of potato
leafhopper, Empgagga fauna, into Wisconsin. Ann. Entomol.
Soc. Am. 57: 588-591.

Pillemer, E.A. & W.M. Tingey. 1976. Hooked trichomes: a
physical plant barrier to a major agricultural pest.
Science 193: 482-484.

Pillemer, E.A. & W.M. Tingey. 1978. Hooked trichomes and

resistance of Ehamlus. mlsam to Empoasca fahae.
Entomol. Exp. Appl. 24: 83-94.

Poos, F.W. 1932. Biology of the potato leafhopper, Empgagga
tibia (Harris), and some Closely related species of
Empgafiga. J. Econ. Entomol. 25: 639-646.

Poos, F.W. & N.H. Wheeler. 1943. Studies of host plants of
leafhoppers of the genus Empgaaga. U.S. Dep. Agric. Tech.
Bull. 850: 1-51.

Poos, F.W. Poos & N.H. Wheeler. 1949. Some Additional host
plants of three species of leafhoppers of the genus
Empgagga. Proc. Entomol. Soc. Wash. 51: 35-38.

Robbins, J.G.,D.M. Daugherty a J.H. Hatchett. 1979. oviposi-
tional and feeding preference of leafhoppers (Homoptera:
Cicadellidae) on Clark soybeans in relation to plant
pubescence. J. Kans. Entomol. Soc. 52: 603-608.

Ross, H.H. 1957. Evolutionary developments in the leafhop-
pers, the insect family Cicadellidae. Syst. 2001. 6: 87-
98.

Ross, H.H. & T.E. Moore. 1957. New species in the Empoasaa
fanag, complex (Hemiptera, Cicadellidae). Ann. Entomol.
Soc. Am. 50: 118-122.

Ross, H.H. 1959. A survey of the Empgaaga,fanag complex
(Hemiptera, Cicadellidae). Ann. Entomol. Soc. Am., 52:
304-316.

JRoss, H.H, G.C. Decker & H.B. Cunningham. 1964. Adaptation
and differentiation of temperate phylogenetic lines from
tropical ancestors in Empgaaga. Evolution 18: 639-651.

Sanford, L.L. 1982. Effect of plant age on potato leafhopper
infestation of resistant and susceptible potato clones.
Am. Potato 59: 9-16.

41

Simmons, A.M., K.v. Yeargan & B.C. Pass. 1984. Development

of the potato leafhopper on selected legumes. Trans. Ky.
Acad. Sci. 45: 33-35.

Simonet, D.E., R.L. Pienkowski, D.G. Martinez & R.D.
Blakeslee. 1978. Laboratory and field evaluation of
sampling techniques for the nymphal stages of the potato
leafhopper on alfalfa. J. Econ. Entomol. 71: 840-842.

Simonet, D.E. & R.L. Pienkowski. 1979. A sampling program
developed for potato leafhopper nymphs, Empgaaga
(Homoptera: Cicadellidae) on alfalfa. Can. Entomol. 111:
481-486.

Simonet, D.E. & R.L. Pienkowski. 1980. Temperature effect on
development and morphometrics of the potato leafhopper.
Environ. Entomol. 9: 798-800.

Sohi, 6.8. 1983. The oriental Typhlocybinae with special
reference to the pests of cotton and rice: a review, pp.
49-74. IN W.J. Knight, N.C. Pant, T.S. Robertson, & M.R.
Wilson (eds.), First international workshop on leafhop-
pers and planthoppers of economic importance. Common-
wealth Institute of Entomology, London.

Singh, B.B., H.H. Hadley & R.L. Bernard. 1971. Morphology of
pubescence in soybeans and its relationship to plant
vigor. Crop Sci. 11: 13-16.

Southern, P.S. 1982. A taxonomic study of leafhopper Genus
Empoasca. (Homoptera: Cicadellidae) in Eastern Peru. N.
Carolina Agr. Res. Serv., Tech. Bull. 272.

Taylor, R.A.J. & D. Reling. 1986. Preferred wind direction
of long-distance leafhopper (Empcasca,fabae) migrants and
its relevance to the return migration of small insects. J.
An. Ecol. 55: 1103-1114.

Tingey, W.M. & R.W. Gibson. 1978. Feeding and mobility of
the potato leafhopper impaired by glandular trichomes of
berthaultii

Salaam and Salaam Wu- J. Econ-
Entomol. 71: 856-858.

Tingey, W.M. & J.E. Laubengayer. 1981. Defense against the
green peach aphid and potato leafhopper by glandular

trichomes of Eglgnnm,hg;§hanl§11. J. Econ. Entomol. 74:
721-725.

Turnipseed, 8.6. 1977. Influence of trichome variations on
populations of small phytophagous insects in soybean.
Environ. Entomol. 6: 815-817.

42

van Schoonhoven, A., G.J. Hallman & S.R. Temple. 1985.
Breeding for resistance to Emppagga Enigmgni Ross and
Moore in Ehaggpln: ynlgazia L., pp. 11-39. IN The leafhop-
pers and planthoppers. L.R. Nault and J.G. Rodriquez
(eds.), John Wiley, New York.

Vidano, C. a A. Arzone. 1983. Biotaxonomy and epidemiology
of Typhlocybinae on vine, pp. 75-85. IN W.J. Knight, N.C.
Pant, T.S. Robertson, and M.R. Wilson (eds.), lst interna-
tional workshop on leafhoppers and planthoppers of econ—
omic importance. Commonwealth Institute of Entomology,
London.

Viraktamath, C.A. 1983. Genera to be revised on a priority
basis. The need for keys and illustrations of economic
species of leafhoppers and preservation of voucher
specimens in recognized institutions, pp. 471-492. IN W.J.
Knight, N.C. Pant, T.S. Robertson, and M.R. Wilson (eds.),
lst international workshop on leafhoppers and planthoppers
of economic importance. Commonwealth Institute of Entomol-
ogy, London.

Wagner, W. 1951. Beitrag zur phylogenies und systmatik der
Cicadellidae (Jassidae) nord-und mittleuropas. Soc. Sci.
Fennica Comment. Biol. 12: 44.

Walgenbach, J.F. & J.A. Wyman. 1984. Dynamic action thres-
hold levels for the potato leafhopper (Homoptera: Cicadel-
lidae) on potatoes in Wisconsin. J. Econ. Entomol. 77:
1335-1340.

Walgenbach, J.E. & J.A. Wyman. 1985. Potato leafhopper
(Homoptera: Cicadellidae) feeding damage at various potato
growth stages. J. Econ. Entomol. 78: 671-675.

Walgenbach, J.F., J.A. Wyman & D.B. Hogg. 1985. Evaluation
of sampling methods and development of sequential sampling
plan for potato leafhopper (Homoptera: Cicadellidae) on
potatoes. Environ. Entomol. 14 231-236.

Wells, P.W., G.P. Dively & J.M. Schalk. 1984. Resistance and
reflective foil mulch as control measures for the potato
leafhopper (Homoptera: Cicadellidae) on Ehaagplna Species.
J. Econ. Entomol. 77: 1046-1051.

Wilson, M.C., J.K. Stewart & H.D. Vail. 1979. Full season
impact of the alfalfa weevil, meadow spittlebug, and
potato leafhopper in an alfalfa field. J. Econ. Entomol.
72: 830-854.

Wolfenberger, D. & J.P. Sleesman. 1961. Resistance in common

bean (Ehaseolua Ynlgaris) lines to the potato leafhopper.
J. Econ. Entomol. 54: 846-849.

43

Womack, c.L. 1984. Reduction in photosynthetic and transpi-

ration rates of alfalfa caused by potato leafhopper
(Homoptera: Cicadellidae) infestations. J. Econ. Entomol.
77: 508-513.

Young, D.A. 1952. A reclassification of Western hemisphere
Typhlocybinae (Homoptera:Cicadellidae). Kans. Univ. Sci.
Bull. 35.

MANUSCRIPT II

INFLUENCE OF BEAN/TOMATO INTERCROPPING ON POPULATION DYNAMICS
OF THE POTATO LEAFROPPER, ElfiQAfiQA [LEAK
(ROMOPTERA: CICADELLIDAE)

44

45

ABSTRACT

The influence of tomato and bean interplanting upon the
potato leafhopper (PLH), Empgiggg, {1213, (Harris), was
studied. A field design incorporating multiple densities of
tomato was used to evaluate the overall influence, and
determine which life stage was principally affected. A
separate study identifying the relationship between bean
foliar density and PLH colonization was also conducted.
Lastly, a laboratory study was conducted to analyze the
potential influence of host plant quality (based on total
plant nitrogen) upon acceptability for oviposition by PLH.

Reduced PLH densities on bean in bean/tomato interplant-
ings were observed. Differences in nymphal counts between
treatments were a function of oviposition, as opposed to
differential nymphal mortality from natural enemies or host
plant resistance. Although bean foliar density based on
differences in plant size varied across treatments in the
interplanting study, it did not appear to account for
differences in PLH densities. In a separate study evaluat-
ing the effect of bean foliar density, no differences were
observed in adult PLH densities per plant among treatments,
which varied greatly in plant and therefore foliar density.
Lastly, reduced bean host plant acceptability was observed
when choice tests using beans grown under different fertili-

zation regimes were conducted. Although tomato may have

46

been directly responsible for reduced PLH densities in the
interplantings, the additional effect of host plant quality

was also demonstrated.

47

INTRODUCTION

The potato leafhopper (PLH), Empeasca.fahae.(narris),
is a polyphagous insect species occurring in North America.
The known number of host plants of PLH is well over 100
species (P003 and Wheeler 1943, 1949). These host plants
represent many different families of perennial and annual
herbs, as well as some deciduous trees and shrubs. Although
the population dynamics of PLH are highly dependent on host
plant species, other factors of potential importance include
host plant density, host plant spatial arrangement, inter-
ference by non-host plants through vegetational diversifica-
tion, plant quality and natural enemy abundance. Such
factors are likely to be interrelated. For instance, plant
quality and microclimate (a product of vegetational density)
can be a function of both plant density and species divers-
ity. Various researchers (Bach 1980, 1981, 1984, Risch
1981, Risch et a1. 1983) have discussed these variables in
terms of representing the underlying factors that provide a
basis for the "resource concentration” and ”enemies hypothe-
sis" set forth by Root (1973, 1975).

In a study evaluating the influence of row spacing (i.e.,
plant density) upon the arthropod fauna of soybean, PLH

nymph and adult densities were strongly affected by plant

48

growth characteristics (Mayse 1978). In that study, plant
treatments varied in leaf area, stem structure, biomass and
yield by plant and by ground surface area.

PLH is also influenced by effects resulting from
vegetational diversification. Lamp et al. (1984) noted that
PLH was less abundant in unmanaged alfalfa plots containing
multiple plant species in contrast to nearly pure alfalfa
stands. The basis for these findings is not Clear.
However, E. kzagmgni, a close relative of the potato
leafhopper, was found to be directly influenced by the
presence of several grass weed species, Elgnaing_ind1ga (L.)

and Lentochloa filllifllmla (Lam.), (Altieri et al. 1977).
The potential importance of host plant "quality"

relative to host plant acceptability by PLH, has been
recognized for many years. Poos and Wheeler (1949) observed
PLH developing on the succulent growth of plant species
previously not considered to be hosts. The succulent state
of these 'plants was unusual, and was apparently a function
of weather conditions that were unusual for the time of
year. variation in PLH populations among bean plants has
been attributed, in part, to host plant vigor (i.eq relative
growth among treatments) (Wells et al. 1984). One explan-
ation is that certain sugars are phagostimulants (Dahlman et

al. 1981). Relative sugar concentrations in bean and potato

have been associated with PLH colonization patterns (DeLong

1938).

49

Although PLH has been studied extensively, little has
been reported on the importance of its parasites. This lack
(3f information may indicate that they are not a particularly
ianortant factor in PLH population dynamics. More is known
about the range of predatory species attacking PLH, however,
little information is available regarding their potential
importance (Martinez and Pienkowski 1982).

Research on the interactions between insect species and
plants in the family Solanaceae is common because of the
extensive alkaloid chemistry and plant volatiles associated
with this plant group. This is particularly true for
tomato, W escalsntum "111.. potato, 821mm
W L., and the species from which they were derived
(D'Arcy 1986). As a companion plant (one which affords
protection for others planted in proximity (Tahvanainen and
Root 1972)), tomato is known to influence insect/host-plant
interactions. Under laboratory conditions, Ehyllgtrgta
Elncligrae Goeze fed less on host plant leaves adjacent to
tomato than alone (Tahvanainen and Root 1972). In the
field, eggs and adults of the diamond-back moth, alntglla
(Ellflfiifilli (L.), occurred at lower densities on cabbage
1rltercropped with tomato than in monoculture (Buranday and
13:03 1975). In that study, tomato appeared to directly
affect the pest. Variation in plant quality did not seem to
be a factor since there was no difference in yield between
treatments, implying little change in the qualitative state

of the host plant due to differential competition or

50

interference between plant species. In terms of chemical
constituents of tomato and other members of Solanaceae,
advances have been made in characterizing their effect on
herbivores (Harborne 1986). The alkaloid tomatine is known
to suppress potato leafhopper consumption when added to
feeding solutions in the laboratory (Dahlman and Hibbs
1967).

Research envolving a bean/tomato/leafhopper system was
stimulated by field observations directed at uncovering
differences in insect/host-plant associations brought about
through interplanting. Preliminary results indicated that
PLH was highly influenced by bean/tomato intercropping,
showing reduced densities on intercropped bean. In terms of
yield advantages and insect pest control, considerable
advantages have been found in intercropping bean and tomato
in Central America (Rosset et al. 1985, 1987).

The objective of this study was to evaluate the
influence of tomato intercropped with bean (Ehafieglna
2319311: L.) upon PLH life stages occurring on bean over a
range of tomato densities. Furthermore, the influence of
bean foliage density and plant quality (based on total
nitrogen) was studied to provide insight into the Observed

differences in the intercropping investigation.

51

Root's (1973,1975) "resource concentration" hypothesis
states that herbivores (esp. specialists‘) are most likely
to be more abundant in pure stands of their host plants.
Typically this has been viewed to be a function of movement
rates in and out of host plant habitat. Although the
present study does not address movement per se, other
laboratory based studies were conducted which specifically
addressed PLH movement with and without tomato and other
non-host plants (see Manuscript III). Even though PLH is
difficult to study in detail under field conditions, the
advantages in investigating this species were: (1) much was
known about the life history and host plant range of this
polyphagous species since it is a commonly studied pest, (2)
its natural occurrence in field plots was nearly guaranteed,
(3) it was easy to rear in lab cultures, and (4) polyphagous
species have been studied less in intercropping systems than

monophagous species.

 

1 Some authors define herbivores as specialists or
generalists based on their host plant range, relative to the
plant species within a particular habitat (Risch et a1.
1983, Letourneau 1986).

len

Wit
the
BBC.

as;

52

METHODS

PRELIMINARY FIELD STUDY: During 1983, snap bean and tomato
were intercropped within a newly planted apple orchard (Fig.
1). The bean and tomato monoculture and diculture field
design included two densities of tomato (Castlehy 105)
interplanted with a single bean (Kentucky Wonder, rust-
resistant) density, one bean monoculture, and a tomato
monoculture divided into two densities. Each plot contained
eight rows of a monoculture or eight paired rows of a
diculture on a trellis composed of wooden stakes 2.2 m in
length, and nylon string. Tomato densities were 45 and 70
cm within row and 2 m between rows. Bean density was 20 cm
within row and 2 m between row. Rows Of bean and tomato in
the diculture treatments were 15 cm apart with 1.8 m between
each pair of rows. The four treatment plots were replicated
as blocks in two sites within the orchard. The purpose of
using two densities of tomato in this preliminary study was
to insure a successful interplanting treatment of bean and
tomato, whereby tomato would not overwhelm bean growth.
During this study, the apple trees were believed to have
little potential influence on the bean/tomato plantings
since they were very small (ca. 1.5 m in height), sparsely
distributed and contained little foliage. Data for nymph
populations in the bean monoculture and two bean/tomato

dicultures were analyzed by a two-factor (i.e.,date and

55!

.umCAUman sou Cusp“: osu gnu:
ousuusoocos cusses ace .cm a: use en a: noduuncoc ouefiou

economuuo as» no“: nousuHsUAC oueaouxceon .ousuasuocos
seen "one: nucofiueouu one .ouecouo on» no accuueooH 03»
Case“: poxoo~n one: eucosueoua .noma Cu coon oce apnea»
and: couceuauou:u unecono anone mo seummdc beam .H .mah

 

 

TIEovlli
5.... A... .2.
.lil attae ol-r elonionlo clot-Pl... e e e e e e |
c —eee Own-aeeenlw — e e —e—e pea - M
mi......u..:..:...: . _ a .. _ east . . . . . h
u......r.... sue unsafeflwa. ..
pleeeflueuie TeeIeelmed rllellvlleb eo-weIIEOe e e e e e e e
.ke' mAleeD—e equal” a q! nlelel aleIe-e" ul ul ebl— e 0 O O O
cos-”0W“... o Name. _. «on _o_ ocean. J o e e e e e
I... .. .3..- 1...... . ._
—e eee eee rOIIHOI-erflhuloelH O O 0 e O
eeeeeeeeeeeeeee e O 0 e O

 

 

 

 

 

   

         
    

     

 

 

seen:

223... III . ”4‘?!” IA \m rim,
2...... cm...» W em

.§S<ILA' Av.' a:«....

 

 

 

seem 22.3...

exp

at

dist
tIea
five
sele
With
the:
seas

tIea

54

treatment) randomized block ANOVA (Snedecor and Cochran
1967). Prior to analysis, data were transformed (Vx+.5),

for compliance with assumptions of analysis of variance.

BEAN/TOMATO INTERPLANTING STUDY: During 1985 and 1986 the
experimental design consisted of four blocks of unstaked
bean and tomato. Each block consisted of four rows of snap
bean (Blue Lake var.) planted at a density of 15 cm within
row, and 1.5 m between rows, and tomato (Sunny var.) planted
at four densities down the length of each block at a
distance of 35 cm from each bean row. Together with a
treatment of bean alone at one end of each block, there were
five treatments per block (Fig. 2). This design was
selected to spatially separate those treatment replicates
with no tomato from those with the highest tomato densities,
thereby minimizing interactions between them throughout the
season. To facilitate distribution of random effects over
treatments, the orientation of the four blocks ("gradients”)
was alternated in a north/south direction. Each block was
separated by a 24 m alleyway which was mowed to maintain
short (less than 10 cm) weed stubble. Plot preparation
consisted of tilling the soil, and applying nitrogen (urea)
at a rate of (72 KG/hectare). Water was applied through a
drip irrigation system. In 1985 water was not always
available as required for irrigation. In 1986, little
supplemental water was required due to adequate rainfall,

particularly in late summer.

55

L———————- 241“ -——-—*%

BLOCK)

. a TB Tflllfipl e .

 

 

 

 

 

 

 

 

ROW 1. -gr I .

Row 2 1 : .1 4 .
C .
Row 3. : : i + : .
Row ‘54. 1 i 1 e -
C.......................

BLOCK II

Q.....0..r.8..fé..fi...8..
. l l l 1 2 4 .
' T T I rI—*E—‘
WITHIN ROW :4 s 1 ; .4 J
PLANT DENSITY ° 4 § ; .l . '
. 4 1 A l A .
. I T T T f .

IQNAIQLMEIEB
T;‘.35

T.- e 65
T.-1 e 1
7".2 e 2

BEANLMEIEB
10

f‘ 29m

 

 

 

 

 

 

 

 

BLOCK)"
0000000000000000000000
AT18JB:
0 U 1 0
J l J L l
0 I I I I I .
L J A l 1 J
I T fir I I
0 0
A 1 l L A I
. I I I I I .
0000000000000000000000
BLOCKIV
00000.0000000000000
1 L A“ 1T2 .
I I I I I
0 0
L J l 1 1 A
I I I I I
0 0
A l l l 1
I I I I II
0 0
%1 i A i
. I I T T T .
000000000000000000.

 

 

 

 

Fig. 2. Sean and

24m

 

tomato intercropped in plots forming

increasing densities of tomato over the length of each
Rows of bean are represented by stars,

and circles identify tomato plants.

of four blocks.

56

In 1985, bean plants within each treatment were sampled
to estimate leafhopper nymphs and natural enemy populations
on 15 dates after true leaf initiation. Ten whole-plant
samples per treatment per block were made using direct
observation from julian date 193 (12 July) through julian
date 208 (27 July). Thereafter ten half-side plant samples
were taken. Egg parasitoids of PLH were monitored using 10
by 20 cm yellow plastic cards treated with Tangle-Trapsh
These cards were hung within and above bean leaves collected
from the field and held in a rearing room to obtain egg
counts, as described later. Tomato was also sampled by
direct observation on seven dates throughout the season to
estimate natural enemy occurrence. Four tomato plants in
each treatment replicate were sampled by detailed inspection
of one-half of each plant.

In 1986, bean plants were sampled on 10 dates following
initiation of the first true leaves. For the first two
sample dates, all leaves were sampled, and on subsequent
dates three trifoliate leaves from each of 30 plants per
treatment were sampled by direct observation. Tomato was
not sampled in 1986 because results from 1985 indicated that
it was not warranted.

Oviposition by PLH was evaluated throughout the season
in 1985 by removing leaves from each treatment in each of
the four blocks, placing them in florists waterpics and
retaining them within a rearing Chamber provided with
supplemental lighting (16:8, day:night). Daily observations

57

were made for newly hatched nymphs. To obtain additional
oviposition information, three trifoliate stage plants were
grown in four inch pots and placed in the field within each
treatment and removed weekly during 1985 and 1986 seasons.

During both years bean plant leaf area was estimated
weekly. Initially, measurements were obtained using a LI-
COED leaf area meter. Later, they were obtained by visually
comparing trifoliates with photo—copies of leaves of known
size. In 1985, four bean plants were measured per treatment
within each block, for a total of 16 plants per treatment.
In 1986, six plants were measured per treatment within each
block. On four dates in 1985, tomato leaf areas were also
measured, using the leaf area meter. On each date, leaf
areas were taken on one tomato plant in each treatment per
block, for a total of four plants per treatment.

Beans were harvested during both years. Within each
treatment, four/1 m row portions of beans were marked with
ribbon and repeatedly harvested and weighed. This was done
both years. Pods measuring 8 cm or longer were harvested.
Tomatoes were harvested in 1985 but not in 1986. Four
randomly selected tomato plants were repeatedly harvested in

each treatment.

REGIONAL PLH POPULATION DENSITY: Adult populations were
sampled in two alfalfa strips located 30 m east and west of
the two outside intercropping study blocks. This was done

to provide a record of the regional PLH population through-

58

out the season. These population estimates were used to
assist interpretation of results obtained in the intercrop-
ping study across sample dates and between years. Each
alfalfa strip was divided into four sections measuring 4 by
10 m. Beginning in early June, one strip was cut every one
to two weeks throughout the summer. This maintained a
consistent alfalfa age structure throughout the season
within each strip. The adult PLH densities were sampled
using a large plastic can (with an attached catch jar) that
was inverted and placed over alfalfa for 5 min as described
by Cherry et al. (1977). On any given sample date, all but
the most recently cut section in each strip were sampled.
In each strip, a sample (.3 m’) was taken within each
section. Repeated sampling of all three sections per strip
continued until the standard error was 20% or less of the
mean, to provide population density estimates with similar

accuracy over all sample dates.

HOST PLANT DENSITY STUDY: In 1986 the influence of leaf area
density on PLH colonization was evaluated in field plots of
bean planted at three densities. Each density was repli-
cated three times. A square area divided into nine plots
was tilled and fertilized to accommodate three replicates of

each of three treatments. Each plot measuring 3 by 6 m
contained four rows of bean plants. Within row treatment

plant spacings were 8, 22 or 44 cm, and treatments were

randomly assigned to each plot. A three meter bare soil

59

alleyway separated all treatment plots. Plants were
sampled on 8 and 15 September. The late sample dates were a
result of late season (end of July) planting, and cool
August temperatures resulting in slow growth. Twenty plants
were carefully inspected for adult leafhoppers in each
replicate. The plants were small enough to allow observa-
tion of each leaf without disturbing the leafhoppers
present. Down-wind plots were sampled first so that if
leafhoppers were disturbed they would fly to previously

sampled plots.

THE ROLE OF PLANT QUALITY 0N HOST PLANT SELECTION: In the
course of studying the effects of bean/tomato intercropping
on E. fiahag, it was hypothesized that bean plant quality,
which varied across treatments, was an important determinant
of leafhopper colonization. Three indicators were used to
rank bean quality: leaf area per plant, yield, and total
nitrogen. Data for the first two methods of evaluating the
influence of plant quality on E. fahag host plant selection
were obtained from the intercrop field study, while the
latter were obtained from oviposition choice tests conducted
in a greenhouse using plants grown under different fertiliz-
ing regimes.

Bean plants in the latter study were grown in soil
within four liter plastic pots. Three groups of plants were
grown under different nutrient (15-30-15 NPK, Miracle-6rd)

plant food) regimes. Tests were conducted in cages measur-

60

ing 1.6 by 1.0 by 0.7 m in height. They were constructed of
untreated pine lumber and saran screen. Humidity was
maintained above 40% at all times, and temperatures were
between 21 to 29° C . Two plants representing each nutrient
level were placed in a cage forming a circle. In the first
three tests, 10 adult females were released into the cage to
oviposit in bean over a 48 h period. The fourth test
consisted of 30 females placed in the cage for 120 h.
Following each test, leafhoppers were removed from each
plant during an inspection. All plants were then sprayed
with water to dislodge any leafhoppers that were missed
during inspection, and held in a rearing room until the eggs
hatched and nymphs could be counted. For the nitrogen
analysis, two trifoliates or petioles were removed from each
plant and dried at 65° C.

Total nitrogen was determined (standard Kjeldahl
analysis) using leaf tissue in the first two tests, while
leaf petioles were used for nitrogen analysis of the third
and fourth tests. Petioles were used because immature
whiteflies (considered a contaminant) were present on the
leaf surface of the plants used in the third test. A chi-
square analysis was conducted on each Of the four tests for
two reasons: 1) total plant nitrogen in each designated

level varied between tests, and 2) leaves were analyzed in

the first tests, and petioles in the others.

61

FIELD DATA ANALYSIS: During 1985 PLH densities were
estimated using a half bean plant sample. However, the unit
of measurement used during data analysis was the number of
leafhopper inhabitants per unit resource (leaf area) in
contrast to the total number of occupants per plant. This
was calculated by dividing leafhopper nymph counts per half-
plant sample by the average leaf area per half—plant per
replicate. In 1986 the sample unit was three trifoliates
per plant, negating the need to convert from an estimate per
plant to leaf area.

To compare nymph densities across treatments, the
experimental design was analyzed as a split-plot, such that
direction represented the main-plot effect and treatments
designated by tomato density represented the sub-plot
effect. The blocking term in data analysis is based on
pairing field blocks 1 and 2, and 3 and 4 together, whereby
each pair contained field blocks oriented in Opposite
north/south directions (Fig.2). Since tomato density
represented a continuous independent variable, the linear
and curvilinear (quadratic and cubic) effects were analyzed
within the context of the split-plot design (Cochran and Cox
1957). Data collected during each date were analyzed
separately. Data used in the analysis represented the
average nymph density per m2 in 1985, and average nymph
count per three trifoliates in 1986 for each of the four
replicates per treatment. The model residuals (predicted

minus actual values) were used as an indicator of a lack of

a:
an
be
ana
Va:
and
Stat
Tree

K‘ra1

62

compliance with ANOVA assumptions of independently and
normally distributed error. Requirements were met by using
a square root transformation (VYTDT5') on PLH counts.

The mean leaf area per plant for each treatment
replicate (used as a measure of bean plant quality) could
not be directly integrated into the statistical model
because multicollinearity existed between it and tomato
density (Freund and Littell 1981). This was evident when
leaf area was incorporated into the model as a covariate,
whereby linear dependence with tomato density was demon-
strated by the generation of a singular x'x regression
matrix. This relationship existed between the variables
throughout the season. Since bean leaf area could not be
entered into the statistical model as an independent
covariate, a split-plot analysis was conducted first by
using tomato density as the sub-plot independent variable
and then replacing it with bean leaf area for a second
analysis for each sample date. To analyze the relationship
between bean leaf area and tomato density an additional
analysis was conducted using leaf area as an independent
variable and tomato density as a dependent variable. All
analyses were conducted with standard programs of the
Statistical Analysis System (SAS), (SAS Institute, 1985).

Treatment means in 1983 were analyzed using a Waller-Duncan

K-ratio t-test (Waller-Duncan 1969).

63

RESULTS

PRELIMINARY FIELD STUDY: In 1983, PLH population densities

were considerably larger on bean in monoculture than in the
diculture plots (Fig. 3). In addition, monoculture bean
plants exhibited extensive leaf curling and chlorosis
because populations were so large that year. Populations
peaked during early August (julian date 220) followed by a
continuous decline into September. Nymph densities among
the two diculture treatments were nearly identical to each
other. An analysis of the nymph densities, grouped by
treatment over all dates, showed that PLH densities were
significantly greater in the monoculture plots than in
either of the two intercrop densities. Densities in the two
intercrop treatments were not significantly different
(P<0.05, Waller-Duncan preceded by ANOVA, [F=84.5; df=2,27;
P<0.05]).

NYMPH POPULATIONS IN BEAN/TOMATO INTERPLANTING STUDY: In
1985 and 1986 PLH nymph densities were lower in treatments
representing successive increases in tomato densities (Figs.
4 and 5)”. Summary statistics comparing tomato density and

PLH density are presented for both years (Table 1)’.

 

3 See appendix A, fig.1 for illustration of PLH counts
on a per plant basis (compared to leaf area) for 1985.

’ See appendix A, fig. 2 and 3 for a graphical analysis
Of all sample dates.

64

.mpsum monoumucw oumEou\cmon mama cu UHQEmm coon oumuH0mauu
eons» non mane»: nommonmmou oumuon no Hanan: cmoz .m .mfim

meg 2,32,
omw spa cow om.

omN 0mm OVN onN

nEuo largo—van Oonouv
33.30 .2. o~oEo~\coom

AEonvlmcuooae Owgouv _
ecstaoboa 3053\coom I

9.3.300coE comm I

 

 

 

 

SHdWAN .10 HBBWHN NVBW

 

65

OmN

 

.mmma Ca uuoao ousuusuqc oueeou use ousussoocoa so
some «men seen «a non maniac uoaaoammeu oumuoa no nonasz .¢ .mqh

oeN OHN CNN 0 PN OON amp
34.. - . .e
. ooooooooo ’0 e '9‘". l.‘\\ I
3 oo‘. ...\ ' TOP
/ .. ..
/ \b. a
x . b. ION
zl\\£, .e .a.. ..
I \ a
/ \ 100
a l‘ 1
J \\ CID?
,
, a .
s \ low
. s r
N.N I
p... 0:? on
em. I .ros
mm. DIS
mmmp mum: 303.22 a I .

 

 

vaav svzn ,w 33:: SHdmN

66

.mmma Cu uuoua onsunsuqc ounfiou 0cm ousuasuocofi co cameos coon
ovmuaouuuu eons» non egos»: “monogamoa ousuoa uo wenflsz .n .mnu

 

 

OWN OWN OAwN our om.
bLPp p-phbpbbb bbppppppb pp»Ln~Ppanpppbpp\$T°eo
.: r MN
5.. 1A
T W
.00 M
h S
n d
lo; m.
. 11
r H
. Mu
In.— 3
T 34
. I.
NN m m
. I .I . :3
z. 6..» .ON 0
. ql
mm..Yle . mw
mn.nwlu_. . :1
camp SD: sem\.:2 o. I new 8

 

 

 

I I‘ll. I’~‘.c“
a ICICCAI an‘ WUQA-MU (>OZ‘ .F CROWN.

67

.ane can. so ecu-else cue—alooeu no enseoea eeaa.le

 

 

 

 

 

 

use New ease so a.eh~¢:< .uc.cvm as «sac—u.cm.e use any as veto—no. nee—ea
es. uni. me. an. Aw- an. n as. INC. a. aqua:
«. u. u. m. o. n. i n. p.v « eunsauh
o.« e. v." o. «.N o. i p.« N. swab
e.v uv.o« no.9» u—.N« ee.on v. i un.o N. numb
un.pu no.6" uv.vv un.au un.nu e.« i ¢.v «. any
n acolueeuh
o. 5. up.» a." N. e. i e. no.9 u e_ne~m
¢.m no.u so.~ an.vu no.» N. I no.0N un.«u « seaweed—n
«. a.» o." c.— a.» a.» i «. no.0 « Joe—n
lllldflflflflfldfl. “a dduufln
3.. men no.“ «law we; 2: SW mid 31
wdmuqqudlduqmlmqu
«H. «a. am. pm. 0». pm. aw. am. we. ea naval
m.u as.» up.» uv.o uu.m m. a. a. a. « Luneueh
a. u.~ a.« n.« N. N. n. a. a." cash
a.« uu.c« so.NN u~.Nn «.N c. a.” a.N a. swap
ne.NN so.va sown an.aa un.¢u no.9n un.Nu ue.vn an.o— ask
a «cola-ash
a.« v.N o.n RN.» u~.o un.a e.n o.« v. « sans—m
a." u~.n sN.a un.«« 0." ue.uu un.¢« uu.o N." u ce.«oea.:
no.9" an.a nu.» an.» n.« ea.» so.o« uc.n« an.» « moo—m
lllldflflddfllullll .ud .dduadw
am" «ms was vNN an" ad" van. on" Na“

 

 

e>_eeeoose Lose neaesae ensue amen use omen Lea peaceeeea eta sue:

eaelea usage» ee.a_ecep gal»: seaAOAuee_ cacao; Lou

menace <>Oz<

.eeuae ce_~sq

.haqesem
.p e—aeh

de
51
Th

30}

an»;

68

Although leafhopper nymph densities were low in all treat—
ments during both years (especially in 1986), there was a
consistent progression of fewer nymphs with increasing
tomato densities, as indicated by linear and quadratic
effects of tomato densities on nymph densities. This
occurred throughout periods of peak abundance during both
years. In 1986, a marked difference was noted between the
monoculture and all diculture treatments, while among the
diculture treatments the difference was considerably less.
This became particularly apparent when the monoCulture
treatment was eliminated from the statistical analysis. As
a result, although a significant linear treatment effect on
nymph densities was still noted for julian dates 205, 209
and 216, the sums of squares for treatment were reduced by
82, 75, and 81%, respectively. Overall, the relatively
large difference in leafhopper density between the monocul-
ture and diculture treatments, and the small difference
between diculture treatments explain the consistent quad-
ratic effect expressed during analysis of 1986 data. For
all analyses the model r2 ranged from .64 to .92 when tomato
density was used as the independent variable (Table 1).
Significant direction effect was evident during both years.
That is, blocks oriented with the monoculture plot in the
south, had larger populations of PLH.

Additional data analyses considered the correspondence
between bean leaf area and tomato density, and PLH density

and bean leaf area. A representative example of these

NA

P01

Hg
14,

PLH

69

relationships along with PLH and tomato densities are
illustrated in Figure 6. When the above analysis was
repeated, substituting bean leaf area for tomato density,
significant linear effects were noted for all of 1985, and
quadratic effects paralleling those for tomato density were
noted in 1986. The model r2 was consistently less than that
for tomato, however for each date it was at least within 0.2
of the model r2 produced while using tomato density as the
independent variable. When bean leaf area by treatment was
regressed on tomato density, the two were determined to be
inversely related on nearly all sample dates.

Based upon limited tomato leaf area data collected in
1985, it was evident that the proportional difference in
tomato leaf area between treatments was considerable
throughout the entire season, although it declined as the
season progressed. Relative to the high density intercrop,
tomato leaf area proportions, starting with the lowest
density, were .16, .25 and .50 on julian date 191, and .38,
.54 and .82 of the highest tomato density treatment on day

228, the last day measured.

NATURAL ENEMY POPULATIONS: Populations of predators of the
potato leafhopper and other phytophagous species were very
low throughout the 1985 season (Table 2). In addition, only
eight egg parasitoids (family Mymaridae) were found on the
14 color cards used to capture them following emergence from

PL}! eggs in leaf cuttings. There was no indication that

70

 

d
e

 

llLllJlelJLlllJl

 

NYMPHS
SORTIn+.5]
C) 01 C) U)

 

 

 

 

O. 3
0' OO' ' 'Oos j T 030' ' ' 'Ois' ‘ 'fiozo
BEANLEAFAREA(m2)
0.2 0
ES 0
201 o
<( B a
Re 01 9. . ° J
g D D 2 D

 

 

 

0.0 WWW-Um
o— 1.5 B
3'3 1* ° 0 ,4
O. c 1 o a 0
$5
3 5 1
O

Jlllhllllllllllllll L 1 1J L] l l L
D

9.0

 

'TIW'WWWWW'WWWWW'WW'IWrTWWWI‘WWWWW'WWWWW'WWTTW'

00.2 0.5 0.81.11.41.7 2.0 2.3
TOMATO PLANTS PER ROW METER

Fig. 8. Graphical analysis of the relationships between
bean, tomato and PLH nymph density within the
bean/tomato intercrop during Julian date 206, 1986. 1)
nymph density by tomato treatment, 2) bean plant leaf
area by tomato treatment, and 3) nymph density by bean
plant leaf area. Units of measurement are: tomato
plants per row meter, nymph density per 3 trifoliate
sample, and leaf area (m') per bean plant.

71

«use nun anal»: we. ea_=e~ as nausea u

.:euao- emu a-eamseaaa «cane =o>ou co ee_nmau an: ecu-oh a

.eo~alau an: age—a mono no uueaaoee .aoauaoaomu manage a «ea—u on“ sou
usual-u can: ease—m eaoa o—eam .umau u:..ae means cu co eo~alae on: anon a

 

 

 

a. a.“ a e n.— as.“
«.u n.n e c e.» en."
a." a." o v. «.u an.
a. 9.“ e e N. on.
Ahz<al ma<=umzc cog sum.
99:19— zo mu—h—mzma Ski—ME

v.u e.u a. a. s.« an.”
n.u p.v m. n. «.q ca.“
5." 9." c. a.“ 9." on.
n.« a.« m. a. a. an.
a.” a. e.~ a. a. e

 

Aeneas to. son

an un- uu a as ence—m ecu-ohv
«see—mm one.meuaaau one—an: oae_.eoem~:< ouc.-o=.ooeu “coma-oar

Amhz<am co— mum mmmlazv
nz<mn zc mm—a—mzmn mos<=m¢m

 

.caoa 3a.: eoaaqumaoae. eagle. «e uoqa-ueoe “genome—u meuueeeouaou
eucaluaesa mesosea=_ use. can chug—nooeel seen a. can“ u-eameeuaa
coda-an mace—a cue-ea ecu anon :e «sea-eon; see—an can «ooae_ .a cum-h

72

natural enemy populations were different among treatments,
suggesting that they were not responsible for the differ-

ences in leafhopper densities among treatments.

OVIPOSITION MONITORING: A sequential decline in egg
densities occurred across treatment plots, whereby highest
egg counts were obtained from potted bean plants located in
the monoculture plots (Fig. 7). The relative densities of
leafhopper eggs matched well with nymph counts (Fig. 4)
across treatments when considering that the lag period
associated with leafhopper egg development is approximately
seven days during mid-summer temperatures. In addition,
these data were supported by very similar results obtained
when egg data were collected from leaf cuttings of the
actual field plants. These data showed that differences in
leafhopper populations across treatments were largely due to
differential levels of oviposition, thereby emphasizing the

influence of intercrops upon adult activity.

REGIONAL PLH POPULATION DENSITY: PLH population patterns in
nearby alfalfa strips were considerably different between
1985 and 1986 (Fig. 8). In 1985 the population grew slowly
early in the summer and persisted at a relatively constant
density until well into September. In 1986 there was a

large population buildup that persisted until early August,
followed by an abrupt decline. In 1985, there was little

rain during June and July, and the strips had to be

73

.moma vcuuso moan» mouuuoucu ecu cucuua acosueouv :ueo cu
.xoo) non “seam coon coupon non name no noble: see: .p .oam

whca z¢~gafi

 

 

792 ca. :22. 2
omm ovm omm omm ofim oom oms
_ L _ _ _
o
.. .a
\H
.m
-m
I.
.m
-m
as"
a. .p
mm.
an. .m
~m:m2_som\exzeo.
a
j

 

 

 

INVTG use 8993

74

 

: H EAST FIELD STRIP, 1985
101 H WEST FIELD STRIP, 1985

PLH PER 3m2
U1
I L
' \
4'
.1

 

I
J ...
0.: IIUUIIIUTIFIVUUIUUII'UIUUIUVYVIT
N . §—¥ 1986
NE) 3 H1986
'10-1
0: 1
3:1 ..
5-
I ..
_] ..
0- I

 

 

 

O V'I'lIU'T'UU'V'TT'T'U'Y']

 

 

170 180 190 200 210 220 230 240 250

JULIAN DATE

Fig. 9. Mean adult potato leafhopper densities per .3 m2

soil surface in two alfalfa strips.
for each date.

Sample

SEM is (20%

75

irrigated. Overall plant vigor appeared to be maintained at
a relatively high level. In 1986, irrigation was not neces-
sary. In fact, rain occurred very frequently during August.
On julian date 216, the first sign of. fungal (Erxnia
Ifldlsana. (Brefeld) Humber) infected adult leafhoppers
occurred on bean. This was very likely an important factor
in the decline of leafhoppers in alfalfa. On several dates
following the decline of leafhoppers on alfalfa, neighboring
field plots of bean and potato were sampled, and in all
cases those populations were also found to be small.
Therefore, it was apparent that the regional populations of
leafhopper had declined in early August 1986 and that low
August populations were not unique to the intercropping

plots.

THE EFFECT OF BEAN PLANT DISTRIBUTION ON COLONIZATION: In a
test conducted to evaluate the impact of host plant density
on the potato leafhopper colonization, mean adult E, fabae
counts between treatments were not significantly different
during both sample dates (Table 3). Plants during the first
sample period were very small. There was only one trifoli-
ate per plant that was developed 50% or more. Plant quality
among treatments was considered to be very similar. This

assumption was based on general observation and similar

average leaf areas per plant among treatments.

76

Table 3. loan adult potato leafhopper counts per 20
plants in bean plots representing three different
canopy densities.

 

 

 

TREATNENT
PLANT DENSITY NO. 0F 3 PLANT
DATE (NO. PER RON m) ADULTS LEAF AREA
Y 15D
8 SEPT. LOW ( 1.7) 1.7a 1.2 -
" NED. ( 3.4) 1.7a 1.5 -
” HIGH (12.5) 3.6a 2.5 -
15 SEPT LOW ( 1.7) 3.0a 2.8 .115 I'
” NED. ( 3.4) 3.0a 0.0 .124 m'
" HIGH (12.5) 3.4a 2.5 .136 m'

 

No means are significantly different. (P<0.06; one-
way ANOVA [F=1.9; df=2,6; P<0.06] [F=0.4; df=2,6;
P<0.06].

77

GREENHOUSE STUDY OF THE EFFECT OF PLANT QUALITY: Based on a
greenhouse study of the effect of plant quality (relative to
total plant nitrogen) on E. flange oviposition, it was
determined that leafhoppers laid more eggs on plants
containing higher levels of nitrogen. In the first three
tests, over 70% of the eggs were laid in foliage containing
the highest levels of nitrogen (Table 4). In the fourth
test, similar numbers of eggs were laid on the high and
intermediate treatment, while the lowest nitrogen treatment
was the least accepted for oviposition. An evaluation of
percent total nitrogen was conducted on bean in two treat-
ments of the intercropping study. During 1986, on julian
date 218, leaf petiole samples were taken from the monocul-
ture and the second most dense diculture treatment (1.1
tomato/row m) in each block and analyzed for total nitrogen.
The treatment means were 1.8% and 1.3% nitrogen, respec-

tively.

PLANT YIELDS: Bean yield was reduced significantly (P<0.05)
by increased tomato density (Table 5). Paralleling leaf
area for 1986, bean yield of the lowest density diculture
treatment (1.1 tomato/row m) was far lower then the monocul-
ture yield. Although a tomato treatment without bean was
not present, in 1985 the tomato yield on a per plant basis
was similar for all but the highest tomato density.

In 1986, a plot containing only tomato was added to

the end of each intercrop block, as an extension of the high

78

Table 4. Greenhouse study of potato leafhopper oviposition
in relation to bean plant total nitrogen ; conducted as
four separate trials.

 

FERTILIZER TOTAL 3 b No.
TRIAL NO. TREATNENT % NITROGEN % OVIPOSITION EGGS

 

 

 

 

 

1 HIGH 4.3 74 a 27
LOW 1.5 26 b

2 HIGH 4.5 71 a 7
LOW 1.4 29 a

3 HIGH 1.7 78 a 20
NED 1.1 18 b
LOW .9 6 b

4 HIGH 1.8 40 a 160
NED 1.0 43 a
LOW .8 17 b

 

'5 Neasure of nitrogen in trial one and two are based on
leaf nitrogen, while others are based on petiole nitrogen.
Ten female leafhoppers were released into cages for 48 h
in first three trials. Thirty leafhoppers were released
for 120 h in fourth trial.
c Data within trials analyzed by a 6 test (Sokal and Rholf
1982). Percentages followed by the same letter are not
significantly different (P<0.06) by an STP test.

79

.neo.evs no.muae “a.mua. .nmo.ovs ”ma.vuae “m.vuaa .nne.ovs N«H.¢uae “«.euac
canvas ca «meg loam .A<>oz< peace—a e h: couscous secesnnsomuek .mo.evmv
assuage—c a—ucao—u_:u_n use one clsnoo a eunu—I acuuo— clue ha noto-0u usual

.eucs—m w sea canned no on
.aanl tea v son seen no 08 m

 

 

o e.~n he o c.« nm 0 «.n cu."
A c.cn we a a.» an o o.~ on.—
e «.«n we A w.” vc a 0.” no.
a m.nn em a a.” as as v.v on.
I ecu a e.m cow e a.» 9
Away Away AUXV Annual #05 non
ego—r oasuusoccol ego—r oasuusooccl enour ease—m evalohv
one“ no acooaom cmau no «season mam“ acolaeoah
anamur Ob<20b scam—N z<mm

 

.ceca Au—t commoLOaOaca ouelou no mafia—acct
«coaouuuc uc—ucomOLQOL eacolueoaa nosesoasq neon ecu cued—soocol can: a
«o ucqaeqecoo eo—esue emau use exam :. ec—ogh Oasis“ use seen oweso>< .o punch

80

density tomato/bean treatment. Unfortunately, septoria leaf
spot (5:932:11, lyggpersig_8pegazzini) caused such extensive
defoliation of tomato plants in all treatments during mid
August that harvest was not feasible. While the timing of
the disease had little effect on events relative to PLH, it

did prevent the calculation of land equivalent ratios.

81

DISCUSSION

In 1985 there was clearly an inverse relationship
between tomato and leafhopper densities. Although bean
plant size was also inversely related to tomato density,
plant quality could not be used to provide a more likely
explanation since leafhopper densities among treatments
showed a gradual (near linear) progression. A gradual
difference in PLH densities among treatments, resulting from
a direct effect of tomato, would be expected since the first
two diculture treatments had very low tomato densities and
therefore were expected to have a small effect. However, in
1986 there was a large difference in leafhopper densities
between the monoculture and all diculture treatments, while
little change occurred among the diculture treatments. This
association, which could not be explained solely in terms of
a direct tomato effect, was paralleled by differences in
bean host plant size, which was considered to reflect
differences in bean quality among treatments. Based on
these results, the effect of host plant quality appeared to
be an important factor. Results from ovipositional studies
comparing plants grown under low versus high soil fertility,
also support the claim that the observed differences in
leafhopper field populations were partially due to differ-
ences in bean plant quality among treatments.

In terms of the experiment where bean alone was planted
at three different densities, PLH was not highly responsive

to foliar densities of bean. Even if a statistically

82

significant separation of means had occurred through greater
replication during the first sample period, it is noted that
the plants had only one partially expanded trifoliate,
therefore the value of any conclusions under that extreme
condition would be limited. During the second sample period
the plants had three to four expanded trifoliates, and PLH
counts in all three treatments were nearly identical.
Overall, this test provided no evidence that PLH was only
responding to differences in foliar densities of bean across
treatments in the intercrop study.

Results from this study support the resource concentra-
tion hypothesis, in that the presence of tomato did affect
leafhopper colonization of bean. However, the basis for
this result is hypothesized to have been a combined function
of the qualitative status of bean resulting from tomato/bean
interaction, and a direct influence of leafhopper activity
by the presence of tomato.

Overall, it is apparent that the potato leafhopper is
highly sensitive to the qualitative status of its host
plants and perhaps less in their distribution. Host plant
quality has been implicated as an important factor in
several studies involving the potato leafhopper. In a study
of soybean insects, Kretzschmar (1948) noted that potato
leafhopper densities were five times greater in weed-free,
widely spaced fields, than in weedy, closely spaced fields.
The role of non-host vegetation may be argued as the basis

for those results. However, Mayse (1978) reported similar

83

results in weed-free plots of soybean planted at three
different row spacings. In that study, although a decisive
explanation for the results was not available, host plant
quality may have been one factor. Upon review, support for
this is drawn from differences in yield, and the speculation
that the qualitative state of the soybean plants was
reflected by yield differences across treatments. Further
support for the importance of host plant quality was
provided by Wells et al. (1984), who found larger popula-
tions of the potato leafhopper on dry bean that exhibited
enhanced growth following canopy closure in treatments using
a foil mulch. Also, Poos and Wheeler (1949) found potato
leafhopper populations on plants that were previously not
considered to be host plants, but which were in a stage of
development that was atypical for the time of year due to
weather.

With few exceptions, the potential influence of the
qualitative status of the host plant is seldom incorporated
into studies of intercrop systems (Each 1981, 1984). This is
unfortunate since in some cases it is an important deter-
minant of insect pest densities. Even though the inhibition
of pests may be a function of what is considered to be a
reduced qualitative status of their host plant, reflected by
productivity (yield), this should not necessarily be viewed

in a negative sense, for the land equivalent ratio‘ (LER),

 

1. For an excellent presentation of the LER concept,
see J. vandermeer (1981).

84

may be greater for the intercrops. In those systems where
the qualitative status of the host plant plays a key role in
determining pest densities, pest impact will be unpredicta-
ble between locations until the influence of host plant
quality upon herbivore population dynamics is understood.
This is due to regional variation in weather, soil etc.
playing an important part in the qualitative state of host
plants, and therefore crop susceptibility. Interestingly,
it has been reported that tomato yield is little affected
when interplanted with bean, and the two can provide a very
high over-yield (Rosset et al. 1987).

Plant quality is a relative term and for that reason is
difficult to define. It is represented here by productivity
(yield) and total plant nitrogen. It should be realized
that these relationships (e.gq nitrogen and yield) do not
always coincide. Vogtmann et al. (1984) found that
nitrogen source (i.e.,compost or commercial fertilizers) can
qualitatively influence plant nitrogen (NO: in particular).
Furthermore, it was found that if the appropriate cultivars
were selected, plant productivity was equal among treat-
ments. It is of interest to speculate that perhaps the same
situation may occur when intercropping with particular plant
varieties, whereby certain qualitative characteristics of
the host plant may be changed, yet productivity is high and
acceptability by pests is low. While specific plant
combinations can directly impact the potato leafhopper, as

in the case of several grass species negatively influencing

85

E. grggmggi (Altieri et a1. 1977), PLH is highly sensitive
to the qualitative status of its host plants. Results from
this study indicate that a direct tomato influence and host
plant quality are capable of reducing PLH densities on bean.
Since host plant quality varies extensively among vegeta-
tionally heterogeneous habitats (e.g., alfalfa stands and
vegetable intercrops), future research should consider this
factor along with any direct effects of plants associated

with a herbivores' host plant.

86

REFERENCES CITED

Altieri, M.A., A. van Schoonhoven & J. Doll. 1977. The
ecological role of weeds in insect pest management

systems: a review illustrated by bean (Ehaseglnfi.xnlgalla)
cropping systems. Pans 23: 195-205.

Bach, C.E. 1980. Effects of plant density and diversity on
the population dynamics of a specialist herbivore, the

striped cucumber beetle, Agalymma, yi;tata_(Fab.). Ecology
61: 1515-1530.

Bach, C.E. 1981. Host plant growth form and diversity:
effects on abundance and feeding preference of a special-
ist herbivore, Acalxmma, 2111111 (Coleoptera: Chrysomel-
idae). Oecologia (Berlin) 50: 370-375.

Bach, C.E. 1984. Plant spatial pattern and herbivore
population dynamics: plant factors affecting the movement
patterns of a tropical cucurbit specialist (Agalxmma
Lnnubum). Ecology 65: 175-190.

Buranday, R.P. & R.S. Raros. 1975. Effects of cabbage-tomato
intercropping on the incidence and oviposition of the

diamond-back moth, Elntglla, xylgstglla, (L.). Philip.
Entomol. 72: 566-569.

Cherry, R.H., K.A. Wood and W.G. Ruesink. 1977. Emergence
trap and sweep net sampling for adults of the potato
leafhopper from alfalfa. J. Econ. Entomol. 70: 279-282.

Cochran, W.G. & G.H. Cox. 1957 Experimental Designs. John
Wiley, New York.

Dahlman, D.L. & E.T. Hibbs. 1967. Responses of Empoasga
iihfl:.(Cicadellidae: Hommoptera) to tomatine, solanine,
leptine I; tomatidine, solanidine, and demissidine. Ann.
Entomol. Soc. Am. 60: 732-740.

Dahlman, D.L., L.A. Schroeder, R.H. Tomhave & E.T. Hibbs.
1981. Imbibition and survival response of the potato leaf—

hopper, Empgasga_£abag, to selected sugars in agar media.
Entmol. Exp. 8 Appl. 29: 228-233.

87

D'Arcy, W.G. (ed.). 1986. Solanaceae: Biology and systema-
tics. Columbia Univ. Press, New York.

DeLong, D.M. 1938. Biological studies on the leafhopper
Emngaaga fang; as a bean pest. U.S. Dep. Agric. Tech.
Bull. 618: 1-60.

Freund, R.J. & R.c. Littell. 1981. SAS for linear models, a
guide to the ANOVA and GLM procedures. SAS Institute,
Cary, North Carolina.

Harborne, J.B. 1986. Systematic significance of variations
in defense chemistry in the Solanaceae, pp. 328-344. IN
W.G. D'Arcy [ed.l, Solanaceae: biology and systematics.
Columbia Univ. Press, New York.

Kretzschmar, G.P. 1948. Soybean insects in Minnesota with
special reference to sampling techniques. J. Econ.
Entomol. 41: 586-591.

Lamp, W.O., R.J. Barney, E.J. Armbrust & G. Kapusta. 1984.
Selective weed control in spring-planted alfalfa: effect
on leafhoppers and planthoppers (Homoptera: Auchenor-
rhyncha), with emphasis on potato leafhopper. Environ.
Entomol. 13: 207-213.

Letourneau, 0.x. 1986. Associational resistance in squash
monocultures and polycultures in tropical Mexico. Environ.
Entomol. 15: 285-292.

Martinez, D.G. & R.L. Pienkowski. 1982. Laboratory studies
on insect predators of potato leafhopper eggs, nymphs, and
adults. Environ. Entomol. 11: 361-362.

Mayse M.A. 1978. Effects of spacing between rows on soybean
arthropod populations. J. Appl. Ecol. 15: 439-450.

Poos, F.W. & N.H. Wheeler. 1943. Studies of host plants of
leafhoppers of the genus Empoasga, U.S. Dep. Agric. Tech.
Bull. 850: 1-51.

Poos, F.W. Poos & N.H. Wheeler. 1949. Some Additional host
plants of three species of leafhoppers of the genus
Empoasga. Proc. Entomol. Soc. Wash. 51: 35-38.

Risch, S.J. 1981. Insect herbivore abundance in tropical
monocultures and polycultures: an experimental test of two
hypotheses. Ecology 62: 1325-1340.

Risch, S.J., D. Andow & M.A. Altieri. 1983. Agroecosystem
diversity and pest control: data, tentative conclusions,
and new research directions. Environ. Entomol. 12: 625-
629.

88

Root, R.B. 1973. Organization of a plant-arthropod associa-
tion in simple and diverse habitats: the fauna of collards

(Blififilfli,nlfili£§§). Ecol. Monogr. 43: 95-124.

Root, R.B. 1975. Some consequences of ecosystem texture. IN
S.A. Levin, [ed.l, Ecosystem analysis and prediction.
Society for Industrial and Applied Mathematics, Phila-
delphia, Pennsylvania.

Rosset, P., J. Vandermeer, M. Cano P., G. Warrela, A. Snook
& C. Hellpap. 1985. E1 frijol como cultivo trampa
para el combate de fipgfigntgga,gnn11_ Guenee (Lepidoptera:
Noctuidae) en plantulas de tomate. Agron. Costarr. 9: 99-
102.

Rosset, P., I. Diaz, R. Ambrose, M. Cano P., G. Varrela & A.
Snook. 1987. Evaluacion y validacion del sistema de
policultivo de tomate y frijol como componente de un
programa de manejo integrado de plagas de tomate, en
Nicaragua. Turrialba 37: 85-92.

SAS Institude. 1985. SAS user's guide: Statistics. SAS
institute, Cary, North Carolina.

Snedecor, G.W. & W.G. Cochran. 1967. Statistical methods.
Iowa State Univ. Press, Ames, Iowa.

Tahvanainen, J.O. & R.B. Root. 1972. The influence of
vegetational diversity on the population ecology of a
specialized herbivore, Phyllgtrgta,grngifgrag (Coleoptera:
Chrysomelidae) Oecologia (Berlin) 10: 321-346.

Vandermeer, J. 1981. The interference production principle:
an ecological theory for agriculture. BioScience 31: 361-
364.

Vogtmann, N., A.T. Temperli, U. Kunsch, M. Eichenberger & P.
Ott. 1984. Accumulation of nitrates in leafy vegetables
grown under contrasting agricultural systems. Bio. Agric.
and Hort. 2: 51-68.

Waller, R.A. & D.B. Duncan. 1969. A Bayes Rule for the
symmetric multiple comparison problem. J. Am. Stat. Assoc.
64: 1484-1499.

Wells, P.W., G.P. Dively & J.M. Schalk. 1984. Resistance and
reflective foil mulch as control measures for the potato
leafhopper (Homoptera: Cicadellidae) on Enasgglng species.
J. Econ. Entomol. 77: 1046-1051.

NANUSCRIPT III

POTATO LEAFHOPPER, EIEQASQA_EAEAE (HONOPTERA: CICADELLIDAE),
NOVENENT, OVIPOSITION AND FEEDING RESPONSE PATTERNS IN
RELATION TO HOST AND NON-HOST VEGETATION.

89

90

ABSTRACT

Studies were conducted to evaluate the influence of
non-host vegetation upon bean host plant acceptance by the
potato leafhopper (PLH), Empoasga, flange, (Harris), with
emphasis on the influence of tomato. Cage environments in
the laboratory and greenhouse were used to observe PLH
movement and arrestment, and evaluate performance criteria,
including feeding and oviposition.

The presence of tomato vegetation suppressed feeding by
43%, and in oviposition choice tests only 28% of the eggs
were laid on bean in proximity to tomato. Reduced feeding
was a result of considerable residence time on tomato.
Cabbage also reduced PLH oviposition when in proximity to
bean. In choice tests only 32% of the eggs were laid on bean
in proximity to cabbage. There were no differences in the
average length of time on bean during each arrestment bout
in treatment cages containing a combination of bean and
companion plant leaves versus the control containing two
bean leaves. When evaluating leafhopper movement frequency
from surface to surface (i.e., the two leaves and cage
surfaces), no differences were found when comparing the bean
and tomato treatment with the bean control. However, an
overall trend of increased movement frequency did occur with
the inclusion of leaves of many other companion plants. The
importance of evaluating insect/plant interactions based on

multiple criteria are discussed.

9:

INTRODUCTION

The potato leafhopper (PLH), Empoasga,£abae (Harris),
is a member of the subfamily Typhlocybinae (family Cica-
dellidae). Despite its presence within a phylogenetically
advanced group in which most family members have highly
restricted host plant ranges, PLH has an exceptionally large
host plant range (Poos and Wheeler 1943,1949). This species
has well over 100 known host species representing many
different plant families. Because of the extensive host
plant range, including both tree and herbaceous plant
species, PLH occurs in a wide variety of habitats. Except
for economically important plants, the acceptability of host
plants for oviposition and as a food source by adults and
nymphs is not well understood (Poos and Wheeler 1949, Lamp
et al. 1984a, Simmons et al. 1984).

Disparities exist between host plant suitability for
nymphal development and acceptance by adults. For example,
pigweed (Amaranthus.retrgflexus.L.) is capable of supporting
PLH nymphs to maturity in the lab, yet in the field, nymphs
were not found on this weed species (Lamp et al. 1984a).
Furthermore, under the same field conditions they were found
on other weed species, determined to be equally or even less
suitable for nymph development than pigweed in laboratory

studies. The role that less acceptable and non-host plants

92

may play in primary host plant utilization within a diverse
vegetational environment has been suggested as being
important (Lamp et al. 1984b). Whether interactions are due
to host—plant spatial distribution, reduced plant quality
(through plant competition or interference), improved
natural enemy/pest ratios, differences in canopy micro-
climate, or directly through chemical and mechanical
properties of the companion plants themselves is not
understood. A close relative of PLH, E, kraemeri,Ross and
Moore, has been reported to be repelled by the presence of
several grass species, Elgnsing, indiga (L.) and Leptgghlga
filifgrmis (Lam.), (Altieri 1977). Feeding by PLH and other
insect species is affected by the presence of tomatine, a
common alkaloid in tomato (Dahlman et al. 1967, Hsiao 1986).

Studying insect behavior and evaluating an organism's
performance (i.e., oviposition, feeding, etc.) in relation
to an environment's plant species composition may aid in
understanding host plant utilization patterns and facilitate
predictions of PLH activity in various plant community
scenarios. The present study originated from field studies
demonstrating that PLH attained lower population densities
through reduced oviposition on bean plants intercropped with
tomato, compared to bean planted alone (see manuscript II).
In that study populations were sequentially reduced over a
range of treatments representing a series of increased

'tomato plant densities. In addition, studies have indicated

93

that domestic tomato and particularly wild tomato, LYQQDQL:
sicgn hirsntum Mull, negatively influence a number of insect
species (D'Arcy 1986). Plant compounds and structures
(e.g., trichomes) of specific cultivars may adversely affect
potential pests of tomato, while non-pests of tomato may
respond aberrantly to their respective host plants when in
close proximity to tomato (Gentile and Stoner 1968, Gentile
et al. 1968, Tahvanainen and Root 1972, Williams et al.
1980, Dahlman and Hibbs 1967, Dimock and Kennedy 1983).

The objective of this study was to examine the response
of female potato leafhoppers to leaves of a known primary
host plant and other minor or non-host plant species under
caged conditions, thereby providing a better understanding
of the basis for which bean/tomato intercropping influences
PLH, as well as to evaluate the potential of other non-host
plants to do so as well. It was hypothesized that PLH would
exhibit a unique behavioral pattern toward its bean host
plant depending upon the inclusion of different companion
vegetation. To investigate this hypothesis, leafhopper
movement and performance were evaluated. This was accomp-
lished through: (1) the direct observation of female
leafhopper behavior in small cages and residency time in
large cages, (2) monitoring feeding, and (3) quantifying

oviposition in choice and no-choice tests.

94

MATERIALS AND NETHODS

SHORT-TERM OBSERVATIONS OP FEMALE PLH MOVEMENT: Observa-
tions were conducted to quantify PLH behavior (displacement
and arrestment) when exposed to leaves of various plant
species, with and without bean (a primary host plant).
Responses of female PLH obtained from the lab culture were
recorded for a short period of time (15 min), immediately
after an individual was introduced into a cage with leaves
positioned at each end. Cages consisted of a transparent
cylinder made of polyethylene terephthalatel, and end pieces
from plastic petri dishes (Fig.1). Materials to prevent
escape, minimize leaf damage, and provide ventilation and
easy assembly were included in their construction. No
discernable odor was present in the cages, and following
each use at the end of a test day, all cages were washed and
rinsed in distilled water.

An individual female leafhopper was released into a
cage and observed for 15 minutes. Due to the number of
companion plant species evaluated, test groups were arbi-
trarily selected to be run on the same day. Tomato, radish,
squash, and bean composed one test group, while pepper,
corn, cabbage, and bean were present in the other. These
plant species were chosen based on their representation of
separate taxonomic groups. Seven cages were prepared for a

day's run of tests. One cage was set up with two bean

 

1Polyethylene terephthalate is commonly used for
beverage containers.

95,

.peo goes «a peso—a_eom eo>so~ no ooeoeoaa new :.
«outage eo.as>soeeo lam u:_aoseeoo sou oueo nuele < .n .mam

 

 

23w I 953m .2323
mm£m_0 cmmzzwm
nocoEmoa
m_cmos.

l 9.0 39me

 

 

 

coocow carom

 

 

 

 

 

o..o.o>

62.30
329.233... xoam o... xomm
28353.2. maze: can
ill 50.... Eom

man. Eson.

 

96

leaves (control), while the other cages contained either a
bean leaf and non-bean companion leaf, or two companion
leaves of the same plant species at opposite ends of a cage.
For each treatment, three replicates were conducted per day,
and a total of 18 female leafhoppers across dates were
observed per treatment, one at a time. Observations were
conducted from 0800 to 1800 h on each date, and a female was
used only once.

Displacement and arrestment on leaf or cage surfaces
was recorded each minute. Displacement involved either
walking from one surface to another, or relocating on the
same or another surface following flight. The leafhopper
was considered to be in a state of arrestment from the time
she contacted a surface (leaf or cage) until she relocated
onto a different surface by either flying or walking.
Although the occurrence of multiple events within any one
minute period was noted, the time duration of any event less
than one minute was not explicitly recorded. Arrestment
time on bean leaves was nearly always greater than one
minute. Therefore, since tenure on bean was the primary
reason for monitoring arrestment duration, discretizing
(i.e., blocking time) on a one minute basis was justified.
Results include: 1) total number of whole minute periods out
of 15 that an individual remained on a surface, 2) duration
of "arrestment" for each encounter, and 3) frequency of

transitions from one surface to another.

97

Observations were conducted in a room illuminated only
with cool-white fluorescent 40 watt bulbs positioned 1.2 m
over the observation table and approximately .8 m from each
cage. Room temperature ranged from 23 to 27.5° C, and the
relative humidity ranged from 55 to 74%. Each cage/plant
treatment was assigned randomly to a location on the table
surface for each set of tests run on a given day. Tomato
was grown in 12 liter pots, bean plants in 4 liter pots, and
all others in 8 liter pots. Plants were lightly fertilized
each week with Miracle-GIdD (15-30-15) plant food. All

plant species used in this study are presented in Table 1.

LONG-TERM OBSERVATION OF FEMALE LEAFMOPPER ACTIVITY,
INCLUDING FEEDING: Leafhopper residency and feeding was
evaluated over the course of a day (12 h), within the same
cages described above. This was done to determine if
departures in behavior occurred relative to those observed
during the 15 minute study, and to determine if feeding was
altered by the presence of tomato.

These tests were limited to treatments of bean and
tomato. On a given day each treatment (two bean leaves,
bean and tomato, or two tomato leaves) was represented by
three replicates. The experiment consisted of fifteen
replicates of each of the three treatments. Leafhoppers were
placed in the cages at 0800 h and their location within the
cage was recorded every 30 min. until 2000 h. To monitor

feeding over the course of a day, plastic strips of cage

98

Table 1. Species, variety and size of plants used in experiments.

 

 

 

a
PLANT CULTIVAR i LEAF AREA i'lEIGHT
SNAP BEAN BLUE LAKE 1445 cm' 5.2 g
(211222122.rslsaris L.)
CABBAGE EARLIANA 3785 28.2
(firsssica.212r222;.L-)
CORN SILVER SWEET - —
(lg; ggyg L.) hybrid,white
PEPPER CALIFORNIA 1890 15.9
(92221213 LBBEUB.L ) IONDER
RAUISR CRINsoN GIANT 2900 15.3
(Bseheans.saiirsa L.)
SQUASH BURPEE'S BUSH 4142 23.4
(Cagnzbit; lggghgtg Duch.) TABLE QUEEN
TOIATO SUNNY 5541 51.2
(kissesrsicsn

sssnlsntsa.llll-)

 

Pbenology of those plants used in testing ranged from early
flowering to initial fruit set.

Above ground biomass.

99

material measuring 1.2 by 7.0 cm were placed on the bottom
inside of both ends of the cage to collect droplets of
excreta. Since each leaf assumed a vertical position at the
end of a cage, the excreta produced by each leafhopper fell
to the bottom. These strips, held in place by a small piece
of cellophane tape, were removed and placed under a 10x
dissecting microscope. The total number of excreta droplets
were counted. As before, individuals were evaluated
separately, and each leafhopper was used only once. All

plants used for study were grown as previously described.

LEAFHOPPER TENURE WITHIN A LARGE CAGE ENVIRONMENT: Leafhop-
per residency time (tenure) within the context of a large
cage (Fig. 2) and whole plant environment was studied to‘
further quantify the influence of tomato upon leafhopper
movement. A measure was obtained of PLH residency time
within the canopy of three treatments represented by two
bean plants, two bean plants plus a tomato plant, or one
tomato plant. Three large cages were constructed to house
the treatments and monitor residency as a reflection of
catch rate on cage surfaces. Each cage was composed of a
plywood base and top frame, pine vertical supports, saran
screen, transparent vinyl and VelcrdCL All plywood mater-
ials were painted four months prior to use with a tan latex
paint in order to eliminate odors characteristic of plywood.
The sticky panels (30 % of the cage surface), were of clear

vinyl coated with Tangle Trapsl Tests were conducted

Pine Support

Plywood

 

100

                         

Transparent

. ‘
v 0
4 0.0.0.. .94.4.4.4.4.4.4541414545454545404544

  

   

O
0

Vinyl

0
4
004
4040

.3
.90.

x. . I
. 04040404040
4 0

:04

p...

 

     
           

  

010.0.0o0101’.’

000000000 0

0.0.0.0w0w0w03

          
   

04040404040

0...

 

Velcro Trim

Saran Screen

Plywood Base
1.2m1.2m

 

vinyl panels for monitoring

PLH residency on selected plant environments.

104.40o0.010.0.0.0

 

 

    

      

2. A cage with sticky,

aka.

Fig.

101

outdoors on a grass yard from late August through mid
September. Fifteen female leafhoppers were released into
the lower plant canopy of each cage at 1400 h of day one of
each of three trials. During each 46 h test, cage panels
were checked every two hours throughout the day from 0800 to
2000 hours for captured leafhoppers. Leafhoppers were
inactive from 2000 to 0800 hours during late summer condi-
tions, eliminating the need for nighttime observation.
Preliminary tests indicated that with no plants present,
nearly all leafhoppers were caught within two hours. The
maximum plant canopy temperature within the cages for each
respective test period was 28, 30, and 25° C. Tomato plants
were approximately 60 cm in height when the tests were

conducted.

CHOICE AND NO-CHOICE OVIPOSITIONAL TESTS: To evaluate the
impact of companion plants on potato leafhopper oviposition,
choice tests were conducted within cages in a greenhouse.
Cages used for choice and no-choice oviposition tests were
constructed from 5 by 5 cm untreated pine lumber covered
with saran screen mesh. Each cage measured 1.6 by 1 by .7 m
in height. They were placed in a greenhouse and supple-
mental lighting (40 watt, cool-white fluorescent) was
provided from a distance of 2 to 3 meters on either side.
Temperature ranged from 17 to 28° C and humidity was

maintained above 40%.

102

Choice tests were performed using all previously evalu-
ated companion plants, except corn. During each test the
diculture treatment (i.e., bean and companion plants) was
placed at one end of a cage while a bean control was located
at the other end of the cage. Two types of choice tests were
conducted using tomato. First, the leaf area of the bean
control was set equal to the combined leaf area of the
bean/tomato diculture treatment by using variable numbers of
bean plants (i.e., 2 to 4 plants). This test controlled for
total vegetation between treatments. For the second series
using tomato, as well as for tests using other companion
plants, the bean leaf surface in the control and diculture
treatments were equal. Therefore the combined leaf area of
the diculture treatment was more than the bean control. All
tests were conducted in each of two cages within a green-
house. The placement of the bean control versus the
diculture treatment was alternated from the north to the
south end of a cage, between trials. For all choice tests
10 females were placed in each cage on days one and two
(i.e., 20 total PLH's). Each test lasted 72 h, and except
for tomato, tests of each plant species were replicated
eight times. Tomato tests were replicated 12 times.

No-choice oviposition tests were conducted using only
tomato as the companion plant with bean. Two kinds of no-
choice ovipositional tests were conducted. The first was
conducted in the laboratory, under the same conditions that

the small cage observation study was done. Four cages,

103

identical to those used for rearing (.13 m“), were located 1
m from each other, and treatments consisting of one bean
plant or a bean and tomato plant were assigned to each. The
tomato and bean plants used in this study were grown in .6
liter plastic pots. Five female leafhoppers were place in
each cage for 48 h. This test was conducted on five dates.
The second series of no-choice tests was conducted in the
greenhouse using the same large cages used for the choice
tests. Two bean plants and one tomato were arranged in one
cage, while two bean plants were placed in the other. The
tomato plant was positioned so that its nearest leaves were
several cm from touching the bean leaves, and care was taken
to avoid shading the bean plants by the tomato plant.
Treatments were alternated among cages from one test to the
next. Five females were placed in each cage on days one and
two. The tests ran for 72 h, and were replicated eight

times.

POTATO LEAFHOPPER CULTURE: Adult female PLH, l to 3 weeks
of age were used in all tests to assure that they were past
their preovipositional phase (DeLong 1938). They were
obtained from a culture maintained on broad bean (Vina {aha
L.). The parent stock of the culture was collected annually
from various hosts including snap bean, alfalfa, and potato.
Culture cages were .13 m’ in size and kept in a room
maintained at 23 to 29° C, 45 to 80% RH and a light/dark
cycle of 16:8 h.

104

STATISTICAL ANALYSIS: All data were tested for compliance
with assumptions of the analysis of variance. Based on
these results either analysis of variance tests or a rank
transformation procedure was used. The latter approach is
appropriate for data that would be analyzed through tradi-
tional nonparametric methods. It involved the ranking of
data within test days and applying an analysis of variance
(Conover and Iman 1981). Treatment means were tested using
Waller-Duncan K-ratio t-test (Waller and Duncan 1969). All
analyses were conducted by employing the standard programs
of the Statistical Analysis System (SAS) (SAS Institute,

1985).

105

RESULTS

MOVEMENT OBSERVATION STUDIES: Although tests. were run on
two separate test groups (A: tomato, radish, squash, and
bean no. 1 control; and B: pepper, corn, cabbage and bean
no. 2 control), results were combined to facilitate data
summary. To justify this, bean controls used in each test
group were compared using a Wilcoxon two-sample test (Sokal
and Rohlf 1981). The two controls were not significantly
different (P>0.20), so data from treatments of both test
groups were combined for further analysis. The degree of
uniformity of leafhopper performance among the two controls
is apparent in figures 3 and 4. Throughout the results, the
summary of both test group controls are presented as bean
no. 1 and bean no. 2.

Figure 3 shows that for all cage treatments containing
bean leaves (i.e., controls and combination treatments),
the mean number of minutes in which leafhoppers were present
on the combined leaf surfaces, in contrast to the cage
surface, was not significantly different among treatments“.
For treatments consisting entirely of non-host leaves (i.e.,
no bean leaves present), with the exception of tomato and
pepper, significantly less time was spent on plant surfaces.
The least amount of time was spent on cabbage. Although

tomato and pepper are not among those in the extensive host

 

2See Appendix B, Table 1 for means and standard deviations.

106

 

10- - BEAN LEAF 1w:
:1 COMP. LEAF TIME

 

NUMBER OF MINUTES

 

 

 

 

 

 

 

Fig. 3 lean time spent on leaf surfaces during a 16 min
exposure, in observation cages containing either two bean
leaves, two companion leaves, or one bean and one companion
leaf. Bars with same letters are not significantly
different in total height (P<.06: Waller-Duncan preceded by
rank transformation and one-way ANOVA; [F-6.0: df=13,227:
P<0.05]).

107

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

fi

12" /

U) .. /

E; ,-

/"

i: 10 LC

~ b

g . z
< 8- 7 / b
gr /’ a” :7
p— 1 x“ d a” r”
/ C / /
u— 5— c: b ~/ 35.1“ C g 5-
C) d b D: /- /# A; b /-
LLJ '"d // C/ // / /+/
m 4- /c // b/ x/ / //
2 a /b // Pg // / //
3 ~ c .M ././ . ./ ././ ./ //
Z /‘ x/ j /w gV /k
2- / // /( / //
r/ , // ./ /m ./ //
‘ x“ g-./‘ /- /-./4 w- .zsw-
0 / // / A //

,9

a,
6h”:
4%.
"a.
”o,
is.
55,,
92.,
<90
“:5,
“is.
11“:
“*4;
is.

e,
4,,
s,
a.
s.
a.

Fig. 4. Nean number of surface to surface (leaf 1, leaf 2,
or cage) transitions during 15 min, in observation cages
containing either two bean leaves, two companion leaves, or
one bean and one companion leaf. Bars with same letter are
not significantly different (P<0.06; Waller-Duncan preceded
by a one-way ANOVA [F=2.9; df=13,238; P<0.05]).

108

plant lists by Poos and Wheeler (1943, 1949), leathppers
were observed feeding on tomato and occasionally ovipositing
in both tomato and pepper during the course of several
studies.

In terms of the partitioning of time on leaf surfaces in
treatments containing a bean and companion plant leaf, the
actual amount of time spent on the bean leaf was not
significantly different between treatments (P<0.05 Waller-
Duncan; rank transformation). It was apparent that the
previously reported, combined leaf surface time in the
bean/cabbage treatment, was less because of little time
having been spent on cabbage and not due to reduced time on
bean (Fig.3). Although not significantly different,
leafhoppers tended to reside more on bean in the bean/squash
cages compared to the other treatments. Furthermore, PLH
spent very little time on squash or cabbage leaves.

Among the plants used in this study, the presence of
companion leaves did not significantly (P<0.05) alter the
duration of an arrestment bout (i.e., duration of a given
encounter) on a bean leaf, relative to the controls contain-
ing only bean3. All mean arrestment times were within 25 %
of each other.

The number of surface to surface transitions was

significantly (P<0.05) greater than the controls for only a

limited number of treatments (Fig.4). However, the overall

 

3See Appendix B, Fig. 1 and table 2 for details.

109

trend indicated a general increase in movement for nearly

all treatments containing companion plant leaves.

DAY-LONG OBSERVATION RESULTS: When the location of PLH was
observed every 30 min. within the small cages, the frequency
(i fSD) of repeated observations on the same bean leaf
surface in the bean control (R=6.6 15.2), was not signifi-
cantly different (ANOVA, blocking by date, P<0.05) from the
number of consecutive sightings on bean in the tomato/bean
treatment (i=5.8 15.3). This analysis was important since
it was assumed that there was a relationship between
repeated observations and the duration of arrestment on
bean. Results indicated that the mean number of repeated
observations, therefore arrestment, extended several hours
over the course of a day. Therefore, relative to the 15 min
trials, the duration of arrestment was considerably longer
on bean (for both bean controls and bean/tomato treatments)
when leafhoppers were allowed to perform for an extended
period. However, the relative differences between treat-
ments were very similar to those obtained in the 15 minute
continuous observation results.

The transition frequency (2 iSD) among all three
treatments (bean, bean/tomato,and tomato), was significantly
greater (ANOVA, Waller-Duncan, P<0.05) in the tomato treat-
ment (i=10.6 12.3) than in either the bean control (i=4.3
12.3) or bean/tomato treatment (i=5.4 12.4). In part, these

results differed substantially from those obtained during

110

the 15 minute study (Fig. 4). That '13, in the 15 minute
study there were no differences in transition frequency
between any of these treatments. Compared to the bean
control and bean/tomato treatment, PLH transition frequency
increased significantly under long-term exposure within
cages containing only tomato. Table 2 illustrates the
average partitioning of leafhopper residence time during the
12 hour study. No significant time differences were
observed between treatments for residence on vegetation
versus cage surfaces. Within the bean/tomato cage a
considerable amount (ca. 4.3 h) of time was spent on the

tomato leaf surface (Table 2).

FEEDING RESULTS: Leafhopper feeding was significantly
different between treatments (Table 2). Total excreta
production was far greater in control cages containing two
bean leaves than in the bean/tomato and tomato treatments.
When evaluating the difference between the bean/tomato
treatment versus the bean control, it was not apparent that
these results were due to a limit in the amount of food that
could be obtained from the single bean leaf in the bean/-
tomato treatment, since greater than 300 droplets were
produced from individual leaves in 6 of 15 trials in the
bean control. The average amount of feeding on a bean leaf
within the diculture treatment was similar to that occurring

on an individual leaf in the bean control.

111

Table 2. Average time leafhoppers spent on leaves, and excreta
production (droplets) over 12 h, in small cages containing two bean
or tomato leaves, or one bean and one tomato leaf.

 

 

1m
BEAN BEAN/IOIATO roNAro
i’ 180
(Sean) (Tomato)

TIIE (h) ON
INDIVIDUAL 5.5 .12.8 5.1 18.0 4.3.12.7 4.2 .12.4
LEAVES
TllE (h) on
LEAP SURFACES 10.7 .1.7 a 10.4 .11.0 a 8.4 _11.2 a
COIBINEDa
DROPLETS PER
LEAF PER CAGE 189.4 .1150 181.1155 34.151 57.1110
MAL
(UROPLE'rsb
PER CAGE) 378.8 .1241 a 215.1153 5 114.1151 5

 

Within-row means followed by same letter are not significantly
ifferent (P<0.06, Waller-Duncan preceded by a one-way ANOVA).

[F=0.9; df=2,38; P<0.05].

[F=8.8; df=2,38; P<0.06].

0'00.

112

LEAFHOPPER TENURE WITHIN THE LARGE CAGE ENVIRONMENT: The
capture rate of leafhoppers was used to reflect tenure
within the bean and tomato habitats represented in each
treatment. On two out of the three test dates (2 and 13
Sept.), the capture rate curves for leafhoppers in the bean
versus bean/tomato treatments were nearly identical (Fig.
5). However, on 23 August the capture rate in the bean-
/tomato treatment was more similar to the tomato treatment.
The capture rate in the tomato treatment was consistently
greater, thereby reflecting the lowest tenure time across
treatments.

The data are also useful in interpreting the mobility
of female PLH. In the presence of readily accepted host
plants, female PLH reside on them for considerable lengths
of time without extensive movement (i.e., movement in
meters). At the end of each test, all but one or two
leafhoppers were accounted for, indicating that the results
were a function of leafhoppers departing from the foliage

present in the cage.

BEAN/TOMATO, SQUASH, RADISH, PEPPER, CABBAGE CHOICE TESTS:
Representing equal total leaf areas across treatments, the
initial series of bean versus bean/tomato ovipositional
choice tests showed no significant difference (P<0.05)
between treatments, based on the number of eggs per plant

per treatment. The egg count (mean 18D) per bean plant in

113

 

  
    
  
 

23—25 AUG 1986

:1! at
'“.--4L‘
*0“...

‘ewv-e - -e - -e

 

NO. OF PLH

 

2-4 SEPT 1988

  

NO. OF PLH

 

 

    

3 a... BEAN ‘O--'--'"'~.
‘ 4 .4 TOMATO 'm ‘
g m—m BEAN/TOMADO ‘F'T.
1 {W99 ------ ..M.......................... 13- 1 6 SEPT 1986
\ ’ ~
1 2... ‘\ 4 a "IMMQ....s...Mg........'.........
9-1 .k‘\
.- \
6- N“. - 0 - -0 - 0 - -0. g
‘0 - «we - -0 - -0
:3 mmm BEAN

NO. OF PLH

“ e -0 TOMATO

 

 

a BwflgvéTo T j 1 T 1 hw T T j
I 4 6 8 8 10 1 2 2 4 6 8 8 10 1 2
pm am pm am

HOURS FOLLOWING THE RELEASE OF PLH

1

L‘

Fig. 6 Leafhoppers remaining on plant treatments within
cages containing bean, tomato, or bean and tomato plants.
Fifteen female leafhoppers were released into each cage and
their rate of capture on the sides of the cage was
monitored for 48 h.

 

114

the bean treatment was 32.0 +11.1, and 27.5 +14.2 eggs per

plant in the bean/tomato treatment.

In subsequent choice tests using equal numbers of bean
plants among treatments, resulting in greater total foliar
area in the bean/companion-plant treatment relative to the
bean control, significantly (P<0.05) more eggs were laid per
bean plant in the bean control than in the bean/tomato
treatment (Table 3). An effect of tomato was evident since
bean foliage was equivalent between the diculture treatment
and control, demonstrating that PLH were responding to
factors other than resource (bean) availability.

There were also significantly (P<0.05) fewer eggs laid
in the bean/cabbage treatment relative to its bean control
(Table 3). Oviposition in the bean/pepper, squash and
radish treatments was not significantly (P<0.05) reduced.
Furthermore, the combined treatment means for the squash
test showed that a very large number of eggs were laid
during each squash/bean test relative to other treatments

(Table 3).

BEAN/TOMATO NO-CHOICE OVIPOSITIONAL TESTS: The first series
of no-choice oviposition tests were conducted in small
cages, using young tomato plants grown in .6 liter plastic
pots. Mean :80 oviposition in the bean control (i=15.l

111.2) versus bean/tomato (X=13.8 114.3) treatment was not
significantly different (P<0.05).

115

Table 3. Potato leafhopper oviposition choice tests.
Paired comparisons represented: bean with companion
plants compared to a bean control.

 

 

 

 

 

 

 

a i NYNPHsb

TREATMENT PER REP. (x) :80 NO.(REPS.)
TOMATO/BEAN 17.3 a (28) 12.5 12
BEAN 45.6 b (72) 17.3
PEPPER/BEAN 23.0 a (43) 20.4 8
BEAN 30.9 a (57) 23.8
SQUASH/BEAN 45.0 a (50) 15.8 8
BEAN 46.1 a (50) 23.5
RADISH/BEAN 30.5 a (39) 22.1 8
BEAN 47.6 a (61) 28.8
CABBAGE/BEAN 16.4 a (33) 26.9 8
BEAN 33.6 b (67) 19.5

 

I Number of bean plants in companion treatments and
bean controls were equivalent.

leans within choice tests followed by the same
letter are not significantly different (P<.06; five,
ANOVA's each blocked by date).
[F=29.0; df=1,11; P<0.05]; [F=0.8; df=1,7; P<0.05]
[F=0.0; df=1,7; P<0.05]; [F=2.16; df=1,7; P<0.05]
[F=4.16; df=i,7; P<0.05].

116

The second series of no-choice‘ tests were run under
similar conditions (i.e.,same plant and cage size) to those
described for the second series of tomato/bean choice tests.
Oviposition was significantly (P<0.05) greater in cages
containing bean (i=46.0, SD=¢23.8) as opposed to those

containing bean and tomato (i=22.2, SD=114.6).

117

DISCUSSION

The events involved in host plant utilization by an
insect have been generally grouped as follows: finding,
examining and consuming (Miller and Strickler 1984).
Finding not only involves an organism making contact, but
also the maintenance of proximity to its host. Examining
relates to testing processes prior to consumption, while
consumption is the act of utilizing a host (e.g., feeding,
oviposition etc.). This study evaluated the interaction of
the potato leafhopper with a host and non-hosts by obtaining
three kinds of information which are related to certain of
these general host plant utilization events. That is,
movement is most closely aligned with the finding process,
residency with the examining process, and feeding and
oviposition with the consumption process. Although these
kinds of information only loosely identify the processes
involved, they provide a multilateral analysis of the
influence of vegetational diversity upon an insect herbi-
vore.

Among bean controls and diculture treatments (except
cabbage), the potato leafhopper resided on foliage (in
contrast to the cage surface) nearly equally across treat-
ments when exposed for short time periods (15 min.).
However, of the time spent on foliage within the diculture
cages per se, over 25% was spent on the companion plant
surface. The squash and cabbage treatments were exceptions.

The importance of this in terms of whether this time would

118

be spent productively (actively feeding, ovipositing etc.)
in a system containing only bean, is not entirely clear
since the bean control consisted of two leaves versus one in
the diculture treatments. It may be hypothesized that
increased time spent on bean controls was a result of bean
leaf area representing a greater proportion of the total
surface area within a cage. However, the hypothesis that
PLH processes are altered by the presence of particular
companion plant leaves was strongly supported by the day
long observation study. Time spent on tomato throughout the
day was considerable and resulted in far less overall
feeding in cages containing both bean and tomato compared to
those containing only bean leaves. Whether feeding was
reduced due to a suppressant effect or to a diversion effect
is unknown. However, the latter appears most likely since
feeding on the bean leaf, within the bean/tomato treatment,
was equivalent to the per leaf feeding in the bean control.
Since tomatine has been identified as a feeding suppressant
of the potato leafhopper when incorporated into feeding
solutions, it would be of interest to determine if "food
searching" thresholds are altered when residing on tomato
(Dahlman and Hibbs 1967). Again, this possibility is
supported by the similarity of average per leaf feeding on
bean, in the control and bean/tomato treatments. The small
cage observation and feeding studies would have been
enhanced by the use of a second control consisting of a

single bean leaf, to control for bean leaf area.

119

Oviposition choice tests also demonstrated the potential
of tomato, as well as cabbage in reducing oviposition. The
two kinds of oviposition tests using tomato 9(i.e.,equal
total leaf areas between treatments in contrast to equal
bean leaf area plus tomato) indicated a lack of influence
(either positive or negative) by vegetational concentration.
Tests directed at the combined influence of tomato and
cabbage could prove useful in decreasing oviposition even
further if the effects are synergistic.

Risks associated with increases in transition frequency
due to non-host plant vegetation need to be considered under
field conditions. The general pattern of increased transi-
tion frequency within cages containing non-host plant
foliage indicates that additional movement may commonly be
an important result of introducing companion plants.
However, in the case of tomato this appeared to not be true.
In the 15 min observation study, the day-long observation
study, and the outdoor large cage leafhopper residency
study, the difference in leafhopper movement between the
bean control and the bean/tomato treatments were small or
non-existent.

In this study one test provided inconsistent results
concerning the potential influence of tomato. The small
cage, no-choice oviposition test indicated that tomato had
no influence on oviposition, while both the choice and no-

choice tests conducted within large cages in the greenhouse

120

indicated a significant negative effect. This may be
explained by the fact that the tomato plants used in the no-
choice test were small and at an early stage of phenological
development. In terms of the influence of host plant
phenology upon the PLH, the importance of phenology has been
pointed out for bean and potato (DeLong 1938, Sanford 1982).

Results from field studies (see manuscript II), combined
with those reported here indicate that the influence of
bean/tomato intercropping on PLH involves a combination of
altered host plant quality, through plant competition or
interference, and the direct influence of tomato. These
results indicate that tomato can reduce potato leafhopper
feeding and oviposition. The means by which this occurs may
be based upon a kind of diversion. Residency time data
corresponded most closely to these findings, whereas
movement frequency data provided the least support for
influence by tomato.

The importance of using more than one criterion to
evaluate the impact of companion plants upon a herbivore is
clear. That is, it is inappropriate to assume a particular
outcome (i.e., more or fewer insects) based upon an evalua-
tion of a single criterion, since one response when combined
with various other events may lead to different outcomes.
For instance, even though leafhoppers moved more frequently
in the presence of squash, the majority of their time was

spent on bean in the bean/squash combination tests.

121

Furthermore, it was demonstrated in the oviposition choice
test that little difference existed between the bean control

and bean/squash treatment.

122

REFERENCES CITED

Altieri, M.A., A. van Schoonhoven & J. Doll. 1977. The
ecological role of weeds in insect pest management

systems: a review illustrated by bean (Ehaseglus.xulgsris)
cropping systems. Pan 23: 195-205.

Conover, W.J. & R.L. Iman. 1981. Rank Transformations as a

bridge between parametric and nonparametric statistics.
Am. Stat. 35: 124-133.

D'Arcy, W.G. (ed.). 1986. Solanaceae: biology and systema-
tics. Columbia Univ. Press, New York.

Dahlman, D.L. & E.T. Hibbs. 1967. Responses of Empoasca
Lina: (Cicadellidae: Homoptera) to tomatine, solanine,

leptine I; tomatidine, solanidine, and demissidine. Ann.
Entomol. Soc. Am. 60: 732-740.

DeLong, D.M. 1938. Biological studies on the leafhopper

Empoasca fabag as a bean pest. U.S. Dep. Agric. Tech.
Bull. 618: 1-60.

Dimock, H.H. & G.C. Kennedy. 1983. The role of glandular

trichomes in the resistance of Lyggpgrsiggn,hirsntgm F.
Qlabratum to fleligthis zea. Entomol. Exp. & Appl. 33: 263-
268.

Gentile, A.G. & A.K. Stoner. 1968. Resistance in Lycgper;
siggn spp. to the tobacco flea beetle. J. Econ. Entomol.
61: 1347-1349.

Gentile, A.G., R.E. Webb & A.K. Stoner. 1968. Resistance in
Lycgpersicgn and Solannm, to greenhouse whiteflies. J.
Econ. Entomol. 62: 834-836.

1969. Lyggpgrsiggn and Sglannm spp. resistant to the
carmine and the two-spotted spider mite. J. Econ. Entomol.
62: 834-836.

Hsiao, T.E. 1986. Specificity of certain chrysomelid beetles
for Solanaceae, pp. 345-363. IN W.G. D'Arcy [ed.l,

Solanaceae: biology and systematics. Columbia Univ. Press.
New York.

Lamp, W.O., M.J. Morris & E J. Armbrust. 1984a. Suitability
of common weed species as host plants for the potato

leafhopper, Empoasca tapas. Entomol. Exp. Appl. 36: 125-
131.

123

Lamp, W.O., R.J. Barney, E.J. Armbrust & G. Kapusta. 1984b.
Selective weed control in spring-planted alfalfa: effect
on leafhoppers and planthoppers (Homoptera: Auchenor-
rhyncha). with emphasis on potato leafhopper. Environ.
Entomol. 13: 207-213.

Miller, J.R. & R.L. Strickler. 1984. Finding and accepting
host plants, pp. 128-157. IN W.J. Bell & R.T. Carde'
[eds.], Chemical ecology of insects. Sinauer Associates
Inc., Mass. '

Poos, F.W. & N.H. Wheeler. 1943. Studies of host plants of
leafhoppers of the genus Empoasca. U.S. Dep. Agric. Tech.
Bull. 850: 1-51.

Poos, F.W. Poos & N.H. Wheeler. 1949. Some additional host
plants of three species of leafhoppers of the genus
Empoasga, Proc. Ent. Soc. wash. 51: 35—38.

Sanford, L.L. 1982. Effect of plant age on potato leafhopper
infestation of resistant and susceptible potato clones.
Am. Potato 59: 9-16.

Simmons, A.M., K.v. Yeargan & B.C. Pass. 1984. Development
of the potato leafhopper on selected legumes. Trans. Ky.
Acad. Aci., 45: 33-35.

SAS Institude. 1985. SAS user's guide: Statistics. SAS
institute, Cary, North Carolina.

Sokal, R.R. & J.F. Rohlf. 1981. Biometry. 2nd ed. W.H.
Freeman and Co., San Fransisco.

Tahvanainen, J.G. & R.B. Root. 1972. The influence of
vegetational diversity on the population ecology of a
specialized herbivore, Ehyllgtrgta crucifgzag (Coleoptera:
Chrysomelidae) Oecologia (Berlin) 10: 321-346.

Waller, R.A. & D.B. Duncan. 1969. A Bayes Rule for the
symmetric multiple comparison problem. J. Am. Stat. Assoc.
64: 1484—1499.

Williams, W.G., G.C. Kennedy, R.T. Yamamoto, J.D. Thacker &
J. Bordner. 1980. 2-Tridecanone: a naturally occurring

insecticide from the wild tomato LXQQDSIELQQD. hllfintnm,f.
glabratum. Science. 207: 888-889.

124

CONCLUSIONS

Information from intercropping studies, and insect/-
plant interactions in general, provides strong support for
the overall potential of facilitating pest management
through intercropping. Although the research presented here
does not provide a complete picture of the cause and effect
relationships, it does give considerable insight into the
complexity of a system representative of intercropping. It
is apparent that future work will commonly uncover multiple
causes for results encountered in intercropping. For
example, in this study it is evident that both host-plant
quality and the direct influence of tomato were important
factors in reducing leafhopper impact within the inter—
cropped plots. It is also apparent that effects can
influence one of many activities of a pest, which may result
in reduced pest impact. For example, laboratory evidence
indicated that the potato leafhopper fed less when tomato
was present, while the more commonly studied issue of
movement appeared less important.

Illustrated by direct interactions between insect and
companion plant species, and interspecific plant inter-
actions affecting herbivores through changes in the host
plant, the complexity of intercropping research requires the

development of guidelines. Risch (1983) addressed this need

125

by emphasizing the importance of pest-free controls to
provide clear comparisons among treatments because of the
effect of pest damage over the course of the season. In
this study, an influence of plant damage over the season was
not an issue of particular importance, since the potato
leathpper populations during 1985 and 1986 were not large
enough to cause any signs of plant feeding damage (leaf
burn, leaf curl, and/or chlorosis).

In the opinion of this author, at least one additional
guideline is needed. That being the incorporation of non-
competitive spacing arrangements of the intercrop plants as
well as their respective monocultures. At least some
intercrop treatments within an experimental design should
have plants that are qualitatively similar to those grown in
monoculture. This would allow the separation of direct and
indirect companion plant effects. Furthermore, yield data
(and other measures of plant performance) should always be
collected and reported. This is often lacking in many
studies.

The topic of intercropping has been controversial. Its
practicality within a mechanized system of crop production
is often questioned. Issues of economics are also raised.
For example, concern is expressed toward the simultaneous
production of two crops of unequal value and its impact on
profits. Furthermore, there exists a reluctance in believ-
ing that intercropping or similar forms of manipulating

agricultural systems can significantly reduce pest impact.

126

This viewpoint continues to plague the field of biological
control, whereby there are those who believe that the
currently documented examples of biological control are
little more than attractive oddities. Perhaps when viewed
within the broad context of all factors playing into
agricultural viability (i.e., in terms of economics and long
term sustainability), the currently perceived problems
associated with intercropping will be offset by an array of
benefits, including reduced pest abundance and reduced
reliance on pesticides.

The manipulation of an agroecosystem's vegetational
composition is likely to provide striking, easily inter-
preted results in a limited number of cases. Such results
arise from what could be classified as "big effects". They
can be achieved even with little knowledge of a system's
dynamics. In most fields of science they are pursued early
on, and act to justify further investigation within the
general area of inquiry. However, in the long run advances
are realized in smaller steps. I believe this to be
generally true in pest management research and the role that
crop diversification can play in managing pests. On an
insect behavior basis, important effects resulting from
manipulating an insect's environment are frequently not
going to be recognized by striking responses such as
immediate death, rapid aversion, etc. At the population

level, the identification of important effects are not going

127

to be solely reflected by changes in one kind of response
(e.g., immigration and emigration) in all systems.
Pronounced successes in pest control through inter-
cropping and similar methods will require the cooperative
interaction of individuals in all areas of crop protection
and production. To provide continuity, a systems approach
is necessary so that all important components are identified
and goals can be appropriately set. An important role of
modeling within the context of a SYSTEMS APPROACH is that of
identifying system components that are most responsible for
a system's performance, and most in need of continued
research. The importance of using modeling as an aid in
system identification has been generally overshadowed by
emphasis on precise predictions. It can provide a common
ground among researchers and an organized and disciplined
exploration into identifying properties of a system.
Overall, this study supports the viewpoint that the
value of intercropping in pest control is through specific
interactions brought about by the appropriate selection of

plants, and not by general, nonspecific diversification.

81 BL I OGRAPHY

128

BIBLIOGRAPHY

Adler, P.H. 1982. Nocturnal occurrence of leaf hoppers
(Homoptera: Cicadellidae) on soil. J. Kans. Entomol. Soc.
55: 73-74.

Altieri, M.A., A. van Schoonhoven & J. Doll. 1977. The
ecological role of weeds in insect pest management

systems: a review illustrated by bean (Ehaseglna xnlgalifi)
cropping systems. Pan 23: 195-205.

Ahmed, H. 1983. Biotaxonomy of Typhlocybine leafhoppers of
Pakistan, pp. 179—187. IN W.J. Knight, N.C. Pant, T.S.
Robertson, & M.R. Wilson [eds.], First international
workshop on leafhoppers and planthoppers of economic
importance. Commonwealth Institute of Entomology, London.

Bach, C.E. 1980. Effects of plant density and diversity on
the population dynamics of a specialist herbivore, the

striped cucumber beetle. Acalxmma Xiltflifl.(Fab.). EcologY
61: 1515-1530.

Bach, C.E. 1981. Host plant growth form and diversity:
effects on abundance and feeding preference of a special-
ist herbivore, Agalymma gigging (Coleoptera: Chrysomel-
idae). Oecologia (Berlin) 50: 370-375.

Bach, C.E. 1984. Plant spatial pattern and herbivore
population dynamics: plant factors affecting the movement
patterns of a tropical cucurbit specialist (Acalxmma
innnhnm). Ecology 65: 175-190.

Backus, E.A. 1985. Anatomical and sensory mechanisms of
planthopper and leafhopper feeding behavior. 163-194. IN
L.R. Nault and J.G. Rodriquez (eds.), The leafhoppers and
planthoppers. John Wiley, New York.

Beirne, B.P. 1956. Leafhoppers (Homoptera:Cicadellidae) of
Canada and Alaska. Can. Entomol. 88: 1-180 (suppl. 2).

Buranday, R.P. & R.S. Raros. 1975. Effects of cabbage—tomato
intercropping on the incidence and oviposition of the

diamond-back moth, Elntglla, xylgstglla (L.). Philipp.
Entomol. 2: 369-374.

129

Cancelado, R.E. & E.B. Radcliffe. 1979. Action thresholds
for potato leafhopper on potatoes in Minnesoda. Econ.
Entomol. 72: 566-569.

Chalfont, R.D. 1965. Resistance of bunch bean varieties to
the potato leafhopper, and relationship between resistance
and chemical control. J. Econ. Entomol. 58: 681-682.

Cherry, R.H., K.A. Wood and W.G. Ruesink. 1977. Emergence
trap and sweep net sampling for adults of the potato
leafhopper from alfalfa. J. Econ. Entomol. 70: 279-282.

Chumakova, B.M. 1960. Adult feeding as a factor of increase
in efficiency of insect pest parasites. Trudy Vsesoyuznogo
Instituta Zashchity Rastenii 15: 57—70.

Clausen, C.P. (ed.) 1978. Introduced parasites and predators
of arthropod pests and weeds: a world review. USDA
Handbook. 480.

Cochran, W.G. & G.M. Cox. 1957. Experimental designs. John
Wiley, N.Y.

Conover, W.J. & R.L. Iman. 1981. Rank Transformations as a
bridge between parametric and nonparametric statistics.
Am. Stat. 35: 124-133

Cuperus, G.W., E.B. Radcliffe, D.K. Barnes, & G.C. Marten.
1983. Economic injury levels and economic thresholds for
potato leafhopper Ean§§£§.£ihig.(Homoptera: Cicadellidae)
on alfalfa ugdigagg,sa§1ya in Minnesota. J. Econ. Entomol.
76: 1341—1349.

D' Arcy, W.G. (ed.). 1986. Solanaceae: biology and system-
atics. Columbia Univ. Press, N.Y.

Dahlman, D.L. 5 E.T. Hibbs. 1967. Responses of Empoasga_
iihflg (Cicadellidae: Hommoptera) to tomatine, solanine,
leptine I; tomatidine, solanidine, and demissidine. Ann.
Entomol. Soc. Am. 60: 732-740.

Dahlman, D.L., L.A. Schroeder, R.H. Tomhave & E.T. Hibbs.
1981. Imbibition and survival response of the potato leaf—

hopper, Empgasga flange, to selected sugars in agar media.
Ent. Exp. & Appl. 29: 228-233.

De Bach, P. (ed.). 1964. Biological control of insect pests
and weeds. Reinhold Publ.

Decker, G. C., C.A. Kouskolekas & R.J. Dysart. 1971. Some
observations on fecundity and sex ratios of the potato
leafhopper. J. Econ. Entomol. 64: 1127-1129.

130

DeLong, D.M. 1931a. A revision of the American species of

known to occur north of Mexico. U.S. Dep. Agr.
Tech. Bull. 231: 1-59.

DeLong, D.M. 1931b. The more important species of leafhopper
affecting the apple. J. Econ. Entomol. 24: 1214-1222.

DeLong, D.M. 1938. Biological studies on the leafhopper

Empoasca fabae as a bean pest. U.S. Dep. Agr. Tech. Bull.
618: 1-60.

DeLong, D.M. 1971. The bionomics of leahoppers. Annu. Rev.
Entomol. 16: 179—210.

DeLong, D.M., D.J Borror & C.A. Triplehorn. 1981. An
introduction to the study of insects. 5th ed., Science
College, Philadelphia.

Dimock, K.B. & G.C. Kennedy. 1983. The role of glandular
trichomes in the resistance of Lyggpersiggn hirsntnm F.
Qlabratnm to fleligtni§_zea, Ent. Exp. & Appl. 33: 263-268.

Drummond, B.A.,III. 1986. Herbivory and Defense, pp.303-305.
IN W.G. D'Arcy [ed.l, Solanaceae: biology and systematics.
Columbia Univ. Press, New York.

Dysart. R.J. 1962. Local movement of the potato leafhopper
in alfalfa. Proc. N. Cent. Br. Entomol. Soc. Amer. 17:
100-101.

Dworakowska, I. 1979. The leafhopper tribe Zyginellini
(Homoptera, Auchenorrhyncha, Cicadellidae, Typhlocybinae).
Revue Zoologie Africaine. 93: 299-331.

Eckenrode, C.J. & L.P. Ditman. 1963. An evaluation of potato
leafhopper damage to lima beans. J. Econ. Entomol. 56:
551-553.

Ehler, L.E. 1979. Natural enemies of the cabbage looper on
cotton in the San Joaquin valley. Halgardia 45: 73-106.

Elliger, C.A., Y. Wong, B.C. Chan & A.C. Waiss, Jr. 1981.
Growth inhibitors in tomato (Lycopersicon) to tomato
fruitworm (Haligthli zen). J. Chem. Ecol. 7: 753-757.

Elton, C.S. 1958. The ecology of invasions by animals and
plants. Hethuen and Co., London.

Evans J.W. 1966. The leafhoppers and froghoppers of Aus-
tralia and New Zealand ' (Homoptera:Cicadelloidea and
Cercopoidea). Aust. Mus. Hem. 12.

Feeny, R.P. 1976. Plant apparency and chemical defense. Rec.
Adv. Phytochem. 10: 1-40.

131

Fleischer, S.J., W.A. Allen, J.M. Luna & R.L. Pienkowski.
1982. Absolute density estimation from sweep sampling,
with a comparison of absolute-density sampling techniques
for adult potato leafhopper in alfalfa. J. Econ. Entomol.
75: 425-430.

Flinn, P.W. & A.A. Hower. 1984. Effects of density, stage,

and sex of the potato leafhopper Empoasga Lana: (Homop-
tera: Cicadellidae), on seedling alfalfa growth. Can.
Entomol. 116: 1543-1548.

Flinn, P.W., R.A. Taylor & A.A. Hower. 1986. Predictive
model for the population dynamics of potato leafhopper,

Empoasca fabae (Homoptera: Cicadellidae), on alfalfa.
Environ. Entomol. 15: 898-904.

Freund, R.J. & R.C. Littell. 1981. SAS for linear models, a
guide to ANOVA and GLM procedures. SAS Institute, Cary,
North Carolina.

Gentile, A.G. & A.K. Stoner. 1968. Resistance in Lyggpgr-

siggn spp. to the tobacco flea beetle. J. Econ. Entomol.
61: 1347-1349.

Gentile, A.G., R.E. Webb & A.K. Stoner. 1968. Resistance in

Lyggpgrsiggn and Solanmm to greenhouse whiteflies. J.
Econ. Entomol. 62: 834-836.

1969. Lyggpgrsiggn, and Sglannm spp. resistant to the
carmine and the two-spotted spider mite. J. Econ. Entomol.
62: 834-836.

Ghauri, M.S.K. 1983. Scientific name of the Indian Cotton
Jassid. 97-103. IN W.J. Knight, N.C. Pant, T.S. Robertson,
& M.R. Wilson (eds.), First International workshop on
leafhoppers and planthoppers of economic importance.
Commonwealth Institute of Entomology, London.

Gibson, I.A.S. & T. Jones. 1977. Honocultures as the origins
of major forest pests and diseases. IN J.M. Cherrett and
G.R. Sanger (eds.) 18th symposiun of the British Ecologi-
cal Society. Blackwell Sci. Pub., Oxford.

Graham, S.A. 1956. Forest insects and the law of natural
compensation. Can. Entomol. 88: 45.
1959. Control of insects through silvicultural practices.
J. Forestry. 57: 281-283.

Gyrisco, 6.6. D. Landman, A.C. York, B.J. Irwin & E.J.
Armbrust. 1978. The literature of arthropods associated
with; alfalfa: IV. A bibliography of the potato leafhop-
per, Empoasca. tibia (Harris) (Homoptera:Cicadellidae).
Special Pub. 51, Agric. Expt. Stn., Urbana-Champaign, Ill.

132

Hall, R.W. & L.E. Ehler. 1979. Rate of establishment of

natural enemies in classical biological control. Bull.
Entomol. Soc. Am. 25: 280-282.

Hall, R.W., L.E. Ehler & B. Bisabri-Ershadi. 1980. Rate of
success in classical biological control of arthropods.
Bull, Entomol. Soc. Am. 25: 111-114.

Harborne, J.B. 1986. Systematic significance of variations
in defense chemistry in the Solanaceae, pp. 328-344. IN
W.G. D'Arcy [ed.l, Solanaceae: biology and systematics.
Columbia Univ. Press, New York.

Hogg, D.B. 1985. Potato leafhopper (Homoptera: Cicadellidae)
immature development, life tables, and population dynamics
under fluctuating temperature regimes. Environ. Entomol.
14: 349-355.

Horwith, B. 1985. A role for intercropping in modern
agriculture. BioScience. 35: 286-291.

Hower, A.A. & P.W. Flinn. 1986. Effects of feeding by potato
leafhopper nymphs (Homoptera: Cicadellidae) on growth and
quality of established stand alfalfa. J. Econ. Entomol.
79: 779-784.

Hsiao, T.H. 1986. Specificity of certain chrysomelid beetles
for Solanaceae, pp. 345-363. IN W.G. D'Arcy [ed.l,
Solanaceae: biology and systematics. Columbia Univ. Press.
New York.

Huffaker, C.B. 1958. Experimental studies on predation:
dispersion factors and predator-prey oscillations.
Halgardia. 27: 343-383.

(ed.) 1971. Biological control. Plenum press. New York.

Huffaker, C.B. & P.S. Messenger (eds.) 1976. Theory and
practice of biological Control. Academic Press. New York.

Isman, E.B. & S.S. Duffey. 1982a. Phenolic compounds in
foliage of commercial tomato cultivars as growth inhib-
itors to the fruitworm, fleligthis zen. J. Am. Soc. Hort.
Sci. 107: 167-170.
1982b. Toxicity of tomato phenolic compounds to the
fruitworm, Heligtnis,zea. Entomol. Exp. Appl. 31: 370-376.

Johnson, K.B., P.S. Teng & E.B. Radcliffe. 1987. Coupling
feeding effects of potato leafhopper, Emngagga, flange
(Homoptera: Cicadellidae), Nymphs to a model of potato.
Environ. Entomol. 16: 250-258.

Kass, D.C.L. 1978. Polyculture cropping systems: Review and
analysis. Int. Agric. Bull. 32. Cornell University,
Ithaca, NY.

133

Kennedy, G.G. & R.T. Yamamoto. 1979. A toxic factor causing
resistance in a wild tomato to the tobacco hornworm and
some other insects. Ent. Exp. & Appl. : 121-126.

Kieckhefer, R.W. & J.T. Medler. 1964. Some Environmental
factors influencing oviposition by the potato leafhopper,
Empoasga_fabag. J. Econ. Entomol. 57: 482-484.

Kieckhefer, R.W. & J.T. Medler. 1965. Aggregations of the
potato leafhopper in alfalfa fields in Wisconsin. J. Econ.
Entomol. 59: 180-182.

Knight W.J. 1983. The Cicadellidae of S.E. Asia-present
Knowledge and obstacles to identification, pp. 197-224. IN
W.J. Knight, N.C. Pant, T.S. Robertson, & M.R. Wilson
[eds.], First International workshop on leafhoppers and
planthoppers of economic importance. Commonwealth
Institute of Entomology, London.

Kretzschmar, G.P. 1948. Soybean insects in Minnesota with
special reference to sampling techniques. J. Econ.
Entomol. 41: 586-591.

Lamp, W.O., M.J. Morris & E J. Armbrust. 1984. Suitability
of common weed species as host plants for the potato

leafhopper, Empoasga_ flange. Entomol. Exp. Appl. 36: 125-
131.

Lamp, W.O., R.J. Barney, E.J. Armbrust & G. Kapusta. 1984.
Selective weed control in spring-planted alfalfa: effect
on leafhoppers and planthoppers (Homoptera: Auchenor-
rhyncha), with emphasis on potato leafhopper. Envir.
Entomol. 13: 207-213.

Letourneau, D.K. 1986. Associational resistance in squash
monocultures and polycultures in tropical Mexico. Environ.
Entomol. 15: 285-292.

Linnavouri, R. 1959. Revision of the Neotropical Delto-
cephalinae and some related subfamilies (Homoptera). Ann.
2001. Soc. Vanamo 20: 1-370.

Luna, J.M., S.J. Fleischer & W.A. Allen. 1983. Development
and validation of sequential sampling plans for potato
leafhopper (Homoptera: Cicadellidae) in alfalfa. Environ.
Entomol. 12: 1690-1694.

MacArthur, R.H. 1955. Fluctuations of animal populations,
and a measure of community stability. Ecology 36: 533-536.

Mahmood, S.H. & M. Ahmed 1968. Problems of higher class-
ification of world Typhlocybinae (Cicadellidae:Homoptera).
Univ. Stud. 5: 72-79.

134

Martinez, D.G. & R.L. Pienkowski. 1982 Laboratory studies on
insect predators of potato leafhopper eggs, nymphs, and
adults. Environ. Entomol. 11: 361-362.

Maxwell, F.G. & P.R. Jennings (eds.). 1980. Breeding plants
resistant to insects. John Wiley, New York.

May, R.M. 1976. Theoretical ecology: Principles and appli-
cations. Saunders, Philadelphia.

Mayse, M.A. 1978. Effects of spacing between rows on soybean
arthropod populations. J. Appl. Ecol. 15: 439-450.

Mayse, M.A., P.W. Price 8 M. Kogan. 1978. Sampling methods
for arthropod colonization studies in soybean. Can.
Entomol. 110: 265-274.

McKinney, K.B. 1938. Physical characteristics on the foliage
of beans and tomatoes that tend to control some small
insects pests. J. Econ. Entomol. 31: 630-631.

Medler, J.T. 1957. Migration of the potato leafhopper: a
report on a cooperative study. J. Econ. Entomol. 50: 493-
497.

Miller, J.R. & K.L. Strickler. 1984. Finding and accepting
host plants, pp. 128-157. IN W.J. Bell & R.T. Carde'
Ieds.l, Chemical ecology of insects. Sinauer Associates
Inc., Mass.

Moffitt, M.R. & H.T. Reynolds. 1972. Bionomics of Empoasga
aglana DeLong on cotton in southern California. Hilgardia
41: 247-298.

Muller, H.G. 1957. Die wirkung exogener faktoren auf die
zylische formenbildung der insekten, insbesondere der
gattung Enscelis (Homoptera: Auchenorrhyncha). Zool.
Jahrb. Abt. System. 85: 317-430.

Nault, L.R. & J.G. Rodriquez (eds.) 1985. The leafhoppers
and planthoppers. John Wiley, New York.

Newsom, L.D., M.Kogan, F.D. Miner, R.L. Rabb, S.G. Turnip-
seed & W.M. Whitcomb. 1980. General accomplishments
towards better pest control in soybean, pp. 51-98. IN C.B
Huffaker [ed], New technology of pest control. John Wiley,
New York.

Nielson, M.W. 1985. Leafhopper Systematics, pp. 11-39. IN
L.R. Nault and J.G. Rodriquez (eds.), The leafhoppers and
planthoppers. John Wiley, New York.

135

Onstad, D.W., C.A. Shoemaker & B.C. Hansen. 1984. Management
of potato leafhopper, Empgafiga Lana: (Homoptera: Cicadell-
idae), on alfalfa with the aid of systems analysis.
Environ. Entomol. 13: 1046-1058.

Perrin, R.M. & M.L. Phillips. 1978. Some effects of mixed
cropping on the population dynamics of insect pests.
Entomol. Exp. Appl. 24: 385-393.

Pienkowski, R.L. & J.T. Medler. 1964. Synoptic weather
conditions associated with long-range movement of potato
leafhopper, Empoasga flange, into Wisconsin. Ann. Entomol.
Soc. Am. 57: 588-591.

Pillemer, E.A. & W.M. Tingey. 1976. Hooked trichomes: a

physical plant barrier to a major agricultural pest.
Science 193: 482-484.

Pillemer, E.A. & W.M. Tingey. 1978. Hooked trichomes and

resistance of mm: insane. to 2mm fatne-
Entomol. Exp. Appl. 24: 83-94.

Pimentel, D., W.P. Nagel & J.L. Madden. 1963. Space-time
structure of the environment and the survival of parasite-
host systems. Am. Nat. 97: 141-167.

Pimentel, D. 1961. The influence of plant spatial patterns
on insect populations. Ann. Entomol. Soc. Am. 54: 61-69.

Poos, F.W. 1932. Biology of the potato leafhopper,
fabae (Harris), and some closely related species of
Empoasga. J. Econ. Entomol. 25: 639-646.

Poos, F.W. & N.H. Wheeler. 1943. Studies of host plants of
leafhoppers of the genus Empoasga, U.S. Dep. Agric. Tech.
Bull. 850: 1-51.

Poos, F.W. Poos & N.H. Wheeler. 1949. Some Additional host
plants of three species of leafhoppers of the genus
Empgagga. Proc. Entomol. Soc. Wash. 51: 35-38.

Price, P.W., C.E. Bouton, P. Gross, B.A. McPheron, J.N.
Thompson & A.E. Weis. 1980. Interactions among three
trophic levels. Annu. Rev. Ecol. Syst. 11: 41-65.

Rhoades, D.F. 1983. Herbivore population dynamics and plant
chemistry, pp. 155-220. IN R.F. Denno & M.S. McClure
(eds.), Variable plants and herbivores in natural and
managed systems. Academic Press, New York.

Rhoades, D.F. & R.G. Cates. 1976. Toward a general theory of
plant antiherbivore chemistry. Rec. Adv. Phytochem. 10:
168-213.

136

Risch, S.J. 1980. The population dynamics of several
herbivorous beetles in a tropical agroecosystem: the

effect of intercropping corn, beans and squash in Costa
Rica. J. Appl. Ecol. 17: 593-612.

Risch, S.J. 1981. Insect herbivore abundance in tropical
monocultures and polycultures: an experimental test of two
hypotheses. Ecology 62: 1325-1340.

Risch, S.J. 1983. Intercropping as cultural pest control:
prospects and limitations. Environ. Management. 7: 9-14.

Risch, S.J., D. Andow & M.A. Altieri. 1983. Agroecosystem
diversity and pest control: data, tentative conclusions,

and new research directions. Environ. Entomol. 12: 625-
629.

Robbins, J.C., D.M. Daugherty & J.H. Hatchett. 1979.
Ovipositional and feeding preference of leafhoppers
(Homoptera: Cicadellidae) on Clark soybeans in relation to
plant pubescence. J. Kans. 52: 603-608.

Robinson, T. 1979. The Evolutionary ecology of alkaloids,
pp. 413-448. IN G.A. Rosenthal 5 D.M. Janzen (eds.),
Herbivores: their interaction with secondary plant
metabolites. Academic Press. New York.

Root, R.B. 1973. Organization of a plant-arthropod associa-
tion in simple and diverse habitats: the fauna of collards
(Blififilfli Qlfilacfia). Ecol. Monogr. 43: 95-124.

1975. Some consequences of ecosystem texture. IN S.A.
Levin, [ed.l, Ecosystem analysis and prediction. Society

for Industrial and Applied Mathematics, Philadelphia,
Pennsylvania.

Ross, H.H. 1957. Evolutionary developments in the leafhop-

pers, the insect family Cicadellidae. Syst. 2001. 6: 87-
98.

Ross, H.H. & T.E. Moore. 1957. New species in the Empoasca,
fabae complex (Hemiptera, Cicadellidae). Ann. Entomol.
Soc. Am. 50: 118-122.

Ross, H.H. 1959. A survey of the Empoasga,£abae complex
(Hemiptera, Cicadellidae). Ann. Entomol. Soc. Am., 52:
304-316.

Ross, H.H, G.C. Decker & R.B. Cunningham. 1964. Adaptation
and differentiation of temperate phylogenetic lines from

tropical ancestors in Empnasca. Evolution 18: 639-651.

137

Rosset, P., J. Vandermeer, M. Cano P., G. Varrela, A. Snook
& C. Hellpap. 1985. El frijol como cultivo trampa para el

combate de Spgdgptg;a_gnn1a Guenee (Lepidoptera: Noctui-
dae) en plantulas de tomate. Agron. Costarr. 9: 99-102.

Rosset, P., I. Diaz, R. Ambrose, M. Cano P., G. varrela & A.
Snook. 1987. Evaluacion y validacion del sistema de
policultivo de tomate y frijol como componente de un
programa de manejo integrado de plagas de tomate en
Nicaragua. Turrialba 37: 85-92.

Sanford, L.L. 1982. Effect of plant age on potato leafhopper
infestation of resistant and susceptible potato clones.
Am. Potato 59: 9-16.

SAS Institude. 1985. SAS user's guide: Statistics. SAS
institute, Cary, North Carolina.

Scriber, J.M. 1984. Host-plant Suitability, pp. 159-202. IN
W.J. Bell & R.T. Carde' (eds.). Chemical ecology of
insects. Sinauer Associates Inc., Mass.

Sinden, S.L., L.L. Sanford S A.K. Stoner. 1978. Effects of
day length and maturity of tomato plants on tomatine
content and resistance to the Colorado potato beetle. J.
Hort. Sci. 103: 596-600.

Simmons, A.M., K.V. Yeargan & B.C. Pass. 1984. Development
of the potato leafhopper on selected legumes. Trans. Ky.
Acad. Aci., 45: 33-35.

Simonet, D.E., R.L. Pienkowski, D.G. Martinez & R.D.
Blakeslee. 1978. Laboratory and field evaluation of
sampling techniques for the nymphal stages of the potato
leafhopper on alfalfa. J. Econ. Entomol. 71: 840-842.

Simonet, D.E. & R.L. Pienkowski. 1979. A sampling program
developed for potato leafhopper nymphs, Empoasga_fabag
(Homoptera: Cicadellidae) on alfalfa. Can. Entomol. 111:
481-486.

Simonet, D.E. & R.L. Pienkowski. 1980. Temperature effect on
development and morphometrics of the potato leafhopper.
Environ. Entomol. 9: 798-800.

Sohi, 6.8. 1983. Typhlocybines (Homoptera:Cicadellidae:
Typhlocybinae) as pests of plants in north-western India.
IN Proceedings, Second oriental entomology symposium held
at Loyola College, Madras. 99-100 (abstr.).

Singh, B.B., H.H. Hadley & R.L. Bernard. 1971. Morphology of
pubescence in soybeans and its relationship to plant
vigor. Crop Sci. 11: 13-16.

138

Snedecor, G.W. & W.G. Cochran. 1967. Statistical methods.
Iowa State Univ. Press, Ames, Iowa.

Sokal, R.R. & J.F. Rohlf. 1981. Biometry. 2nd ed. W.H.
Freeman and Co., San Fransisco.

Southern, P.S. 1982. A taxonomic study of leafhopper Genus
Emnnasca (Homoptera: Cicadellidae) in Eastern Peru. N.
Carolina Agric. Res. Serv., Tech. Bull. 272.

Tanigoshi, L.K., S.C. Hoyt, & B.A. Croft. 1983. Basic
biology and management components for mite pests and their
natural enemies, pp. 153-202. IN B.A. Croft & S.C. Hoyt
[eds.], Integrated management of insect pests of pome and
stone fruits. Wiley, New York.

Tahvanainen, J.D. & R.B. Root. 1972. The influence of
vegetational diversity on the population ecology of a
specialized herbivore, Phyllgtrgta crucifgrae (Coleoptera:
Chrysomelidae) Oecologia (Berlin) 10: 321-346.

Taylor, R.A.J. & D. Reling. 1986. Preferred wind direction
of long-distance leafhopper (Emunaaca. fabae) migrants and
its relevance to the return migration of small insects. J.
An. Ecol. 55: 1103-1114.

Tingey, W.M. & R.W. Gibson. 1978. Feeding and mobility of
the potato leafhopper impaired by glandular trichomes of

Salamm herihanltii and Salaam nelxadeniim. J. Econ.
Entomol. 71: 856-858.

Tingey, W.M. & J.E. Laubengayer. 1981. Defense against the
green peach aphid and potato leafhopper by glandular

trichomes of Sglannm, berthanltii. J. Econ. Entomol. 74:
721-725.

Turnipseed, 8.6. 1977. Influence of trichome variations on
populations of small phytophagous insects in soybean.
Environ. Entomol. 6: 815-817.

van Schoonhoven, A., G.J. Hallman & S.R. Temple. 1985.
Breeding for resistance to Empoasga, kraemgzi Ross and
Moore in Phaseglns vulgaris L., pp. 11-39. IN L.R. Nault
and J.G. Rodriquez (eds.), The leafhoppers and planthop-
pers. John Wiley, New York.

vandermeer, J. 1981. The interference production principle:

an ecological theory for agriculture. BioScience 31: 361-
364.

van Emden, H.F. 1965. The effect of uncultivated land on the
distribution of cabbage aphid (arexicnrxne.hrassicae) on
an adjacent crop. J. Applied Ecol., 2: 171-196.

139

van Emden, H.F. & G.F. Williams. 1974. Insect stability and
diversity in agroecosystems. Annu. Rev. Entomol. 19: 455-
4750

Vidano, C. a A. Arzone. 1983. Biotaxonomy and epidemiology
of Typhlocybinae on vine, pp. 75-85. IN W.J. Knight, N.C.
Pant, T.S. Robertson, and M.R. Wilson (eds.), lst interna-
tional workshop on leafhoppers and planthoppers of
economic importance. Commonwealth Institute of Entomology.

Viraktamath, C.A. 1983. Genera to be revised on a priority
basis. The need for keys and illustrations of economic
species of leafhoppers and preservation of voucher
specimens in recognized institutions, pp. 471-492. IN W.J.
Knight, N.C. Pant, T.S. Robertson, and M.R. Wilson (eds.l,
lst international workshop on leafhoppers and planthoppers
of economic importance. Commonwealth Institute of Ento-
mology.

Vogtmann, H., A.T. Temperli, U. Kunsch, M. Eichenberger & P.
Ott. 1984. Accumulation of nitrates in leafy vegetables
grown under contrasting agricultural systems. Bio. Agric.
and Hort. 2: 51-68.

Wagner, W. 1951. Beitrag zur phylogenies und systmatik der
Cicadellidae (Jassidae) nord-und mittleuropas. Soc. Sci.
Fennica Comment. Biol. 12: 44.

Walgenbach, J.F. & J.A. Wyman. 1984. Dynamic action thres-
hold levels for the potato leafhopper (Homoptera: Cicadel-
lidae) on potatoes in Wisconsin. J. Econ. Entomol. 77:
1335-1340.

Walgenbach, J.E. & J.A. Wyman. 1985. Potato leafhopper
(Homoptera: Cicadellidae) feeding damage at various potato
growth stages. J. Econ. Entomol. 78: 671-675.

Walgenbach, J.F., J.A. Wyman & D.B. Hogg. 1985. Evaluation
of sampling methods and development of sequential sampling
plan for potato leafhopper (Homoptera: Cicadellidae) on
potatoes. Environ. Entomol. 14 231-236.

Watt, K.E.F. 1965. Community stability and the strategy of
biological control. Can. Entomol. 97: 887-889.

Waller, R.A. & D.B. Duncan. 1969. A Bayes Rule for the
symmetric multiple comparison problem. J. Am. Stat. Assoc.
64: 1484-1499.

Wells, P.W., G.P. Dively & J.M. Schalk. 1984. Resistance and
reflective foil mulch as control measures for the potato
leafhopper (Homoptera: Cicadellidae) on Phasgglus species.
J. Econ. Entomol. 77: 1046-1051.

140

Williams, W.G., G.G. Kennedy, R.T. Yamamoto, J.D. Thacker &
J. Bordner. 1980. 2-Tridecanone: a naturally occurring
insecticide from the wild tomato Lycgpgrsiggn_nirsntnm f.
glabratnm, Sci. 207: 888-889.

Wilson, M.C., J.K. Stewart & R.D. Vail. 1979 Full season
impact of the alfalfa weevil, meadow spittlebug, and
potato leafhopper in an alfalfa field. J. Econ. Entomol.
72: 830-854.

Wolfenberger, D. & J.P. Sleesman. 1961. Resistance in common

bean (Ehasenlus Yulgaris) lines to the potato leafhopper.
J. Econ. Entomol. 54: 846-849.

Womack, c.L. 1984. Reduction in photosynthetic and transpi-
ration rates of alfalfa caused by potato leafhopper,
(Homoptera: Cicadellidae) infestations. J. Econ. Entomo.
77: 508-513.

Young, D.A. 1952. A reclassification of Western hemisphere
Typhlocybinae (Homoptera:Cicadellidae). Kans. Univ. Sci.
Bull. 35.

APPENDIX A

POTATO LEAFHOPPER FIELD STUDY

141

APPENDIX A

.momd Gd ”noon“ OHSUHQUMO 08308 nap—fl QuangOOe—OI

cu Henna cmon Hon acaflhc nonaocumou canyon we named: é .mum
to: .2 E5 255.. 32. 2
0mm ovm onN CNN 0 PN CON om _.
a 111.11 2.. ID
. . m...
a oooooooo ’0. Oo’o o. I
5 .5...D... ... .\
IN MW
e . A
x W
/ \h TV mm
// fl. . Q9
D. a
z \ I
/ \ IA s {C d
u. r s r 3
. .2 H
x .2 no 8
w . E
[OF MN
Nd I . d
—.— D3? INF W
mm. I .. W.
mam. an. a...
mum: 3om\.zo» o. I [I

 

 

 

142

APPENDIX A

Fig. 2. Graphical analysis of 1985 intercrop, E, fang:
nymph populations and bean plant growth by replicate over
successive dates. 1) nymph density by tomato treatment,
2) bean plant leaf area by tomato treatment, and 3) nymph
density by bean plant leaf area. Units of measurement are:
tomato plants per row meter, nymph density per leaf area
(m2); leaf area (m’) per bean plant.

APPE

 

NDIX A

JULIAN DATE 193. 1985

143

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a ”.3
5 :. . 2
0.01“ . ' O O
1 ' O . 3
.oo‘ °- ' ' ' '
10.01 ' ' I fl
'3' aa-
§ Eco-1 1
mo-
za‘ - '
o“: C - I C - . C
o 0.2 0.5 as 1:1 :14 137 in "i3
TOMATO PLANTS PER ROW METER
JULIAN DATE 198. 1985
tom:
‘3 ac-
3 col
5 4.0-3
2.0 '
on} -. IO. .“. C . d
. J. a be
ammo-5
: i
g 0.041 '
3; 1 I . I I
0.021 I I I
m: - I l
—‘°.o.: I' " U"" I 'I T V I 1I
9 am
i 3 col
E «oi
2.0 I 0 .
9.: 9' -,. I "I" -, I .--- n - I
0.2 0.5 as 1.: 13¢ :17 in if.)
TOMATO PLANTS PER ROW METER
JULIAN DATE 203. 1985
10.01
‘i‘ 0.0%
i t 3.0-: . I I
3:33 - ' - - ' '
' . —I II I 0 .
0.0-Jr— h b.
mwmh’)
j i
I C
I D I ' .
0.02" I I .
.oo . I '
I"'I""'V""'I"""""""' ,v.----'-.- .,
10.01
'2 101
fix“ - - '
. ‘ g
2.01 l '
o“ '--- _ 3" 9 W' _ - --'-,
' of: 0:5 ofs if: :34 1.1 2.0 2.3

TOMATO PLANTS PER ROW METER

cont.

NLIAN DATE 207, 1985

 

 

 

 

 

 

 

 

 

 

 

 

 

:o.o~:
72‘ am
0 1
' 3.0-! I
E 54.0: ' ' 0 .
2.0-J .— I . '
D“ II I I P
"m is .TI .10 m
0" "Mme-h
6 I .
0.1-1 U ' I
a; 1 - 2
.
1| I. I I
9‘2‘ l""' "I" """' U' " U ""I "' I
10.0-
3 am
3 0.01 .
i 4.0-: I I . .
1.04 c I - : '
o'c‘ : 'I V V. 'U' '3 I "' U 77" V'? U
0.2 0.3 0.8 1.1 1.4 1.7 2.0 2.3
TOMATO PLANTS PER ROW METER
JULIAN DATE 210. 1985
10m:
"‘1' a0« '
0.0- ' ' I '
s 4.01 . I. . . . I
‘ I I .
:21 P . I
"'4' II .TI .‘is no
0" ”mun-5
l o
0.1: 3 ' I
. . z
I ' I
J ' . O I D
9.2% E "V """ I """ V """ I """ """U "" """ I
10.0:
q a01 '
‘0-1 I .
4.01 o '
2.01 ' '
nn‘ . '

 

 

 

I

' crimes "oiémifimifimifi' 330 its
TOMATO PLANTS PER ROW METER

JULIAN DATE 214, 1985

 

 

 

 

 

 

 

 

"6:5 '63 "636" iii" iicmifvmiomi's
TWATO PLANTS PER ROW METER

APPENDIX A

JULIAN DATE 218. 1985

 

 

 

ufl'i’iu
E
lAA‘A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1
“'3‘ ."'I """ I """'"I""'l"""""'I"""
10.0; . I
I— i g
3 ”'1 o
I 3.0.: . .
540‘ : . o '
D
at- _v_ _" ________________________ 9'
o 0.2 0.5 0.11 1.1 134 117 2.0 2.3
TOMATO PIAN'TS PER ROW METER
JULIAN DATE 221. 1985
10.01 . I
'1? 5.0: ‘
P .
£5- 3: . o .
' 1 I
2.0 '-
°"'m .1. .1. 1. .1. .11 .1. .1- .-
“mun-1')
0.4-
’ 0.3- .
0.2- I
0
0.1- I '
9'9: I' I I' I‘ ' 9' I U ' """'E
1o.o-: 0 '
'q" ao« ,
i‘ 0.03 . '
4.04 I
2.04 ' . I
0.9 v I " I "v I ' "l "I ' 'I' "'1
0.2 0.5 0.11 1.1 1.4 1.7 2.0 2.3
TOMATO PLANTS PER ROW METER
JULIAN DATE 224. 1985
10.04 . '
'-? aoJ '
3 5.04 . .
‘0‘: . . I U
2.0: 0
9.9
a .5 1e '10 b .50 .5 )3 .30
mafia-tun?)
0.4-
0.3- ,
0.2- '
C
01: I '
0'91 ' I I " I '! I I' """ v
10.0- t
'5' and '
E 1.0-1 I I
2.0 ' I
0.2 .......

 

 

 

"of: 035 are '1.'1"1I¢ 137 afomifs

TOMATO PLANTS PER ROW METER

JULIAN DATE 228. 1985

 

 

 

 

 

 

 

 

 

 

 

 

10.0- .
72' 3.0- .
3: so: ' .
is 0.0-‘1 . ’
2-0': . . . .
“a. h .1. 1. 5. 5. :1. .1- '6
"mmhfi
0.4- . .
0.3- ' '
. U
0.2 E g I .
OJ. . .
o'c‘ " 'I"" "' V ' "I" ' I"""" ' I W
10.01
R am '
T 3.0.: . I
E "0'3 I .
32* ' - -
N "'63 "6:5 ' ofsmifi "133' 111" if: "if:
TOMATO PLANTS PER ROW METER
JULIAN DATE 232. 1985
10.0-1
3? ao- -
O 1 .
‘ 0.0-1 . I I
E; 4.0-: I . . ~ ,
2.01 I . I I
9'31. In .1. 'u b is ~11. .1. b
manna-1’1
0.4- . '
0.3- ' '
. U
0.2 E g I .
0.1-. P :
0‘2‘ l l' ' v ' I I "'fi"T" I I
10.01
= ‘0‘ I
O
i T 0.0-j .
E 4.0-: I .
2.0
n;- '

 

 

 

'03 635 do 131" 1:4 13 in" 5::
mm PLANTS PER ROW METER

JJLIAN DATE 239. 1985

 

 

 

 

 

 

 

 

 

113" of: 63 131'"1II 15 afomzia
TOMATO PLANTS PER ROW METER

145
APPENDIX A

Fig. 3. Graphical analysis of 1986 intercrop, E. fabag
nymph populations and bean plant growth by replicate over

successive dates. 1) nymph density:tomato treatment, 2)
bean plant leaf area:tomato treatment, and 3) nymph
density:bean plant leaf area. Units of measurement are:

tomato plants per row meter, nymph density per 3 trifoliate
sample, leaf area (m’) per bean plant.

1 46
APPENDIX A

JUL|AN DATE 188. 1985

 

 

 

 

 

 

 

 

 

 

 

 

 

_. 1 5.3 o
a 3 .
I 8.
i g. 1.0: W
g 0.51
0.0: .
0.“ 0.01 0.02
00:41.0!me
0.0.1-
‘ I
g 0.02- I . I a g
3 1 I | I 1
_‘ 0.011
0m 1 I I 1 I l I 'TT
3. 1.5-1 ' 1
g I ‘0: . . l g a
gig ‘ M, 4—3
05-3
0.9' . . . . . . qw
02 0.3 0.5 1.1 1.4 1.7 2.0 2..)
TOMATO PLANTS PER ROW METER
JULIAN DATE 192. 1986
$7:- 1.54 . . .
.3. 1.0- MIT-r,
3 ‘ "
0.51
0.0“. 11.31 ob: 0.6.:
macaw)
003-

fl
9.
I?

 

 

 

 

a 0.01-1
m‘ V I I I I I I Iv I
72' 3'51 I
I g_ I
i; TO“ I . P
g C —.
0.51
0.3

 

032 033 038 131 134 137 2307233
TOMATO PLANTS PER ROW METER

JUUAN DATE 195. 1986

 

 

 

7’ 1.5
E 1 o; I . I
r ' 3 '...‘¢. ‘ . .
0.51
0.93 . . . .
CAD 0.00 0.10 0.13 0.20
manna-F)
0.2

KAN
AREA
.0
2.1.11-1-
.

 

 

 

 

d
. .

.c‘ y I v I 1 I l’ ' I T
I: T.S'S
o'

$9 1.0-
0.3-
0.: l ‘ -

0.2 035 0311 131 13¢ 137 230 233
TOMATO PLANTS PER ROW METER

JULIAN DATE 198. 1985

 

MS
“The.”
3
I

 

o. I: sin (11: 11.1: 11.20

Immune-(.3)

 

115m
9
- T--

 

W115

“The.”

.0 I“

u 0
--1 .- 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0': l I I T I T I T
0.2 0.3 0.8 I.) 1.6 1.7 2.0 2.3
TOMATO PLANTS PER ROW METER
JULIAN DATE 202. 1986
.. °
:5 ”'2 .
C 10.‘ I. . . I
1 '8
5....
0.3“” TS ITI 0.15 0:10
”mane-1')
“4 I
g N} ' I .
I I I .
e'c‘ l I I I I ' I I I
i 1 o
i" 3" :
E I 1.0' M
i .
0.5-
0.3 v-vv ' rv' I I' l 'I V '
0.2 0.3 0.8 1.1 1.4 1.7 2.0 2.3
TOMATO PLANTS PER ROW METER
JUUAN DATE 205. 1986
:15: I f P
i: 1.0: . . f
5 0.53
0:11.111: on I'm an no
~11me
"1 .
I I
a; 0.1-1 . .
1 I I .
0‘3: I I ' I I I v "T' ' 1' 1
:9- L3- MI.
E 3 1.0- ' .
5 0.5-
11.33

 

 

 

0'2 0'3 033 131 134 137 230333
TOMATO PLANTS PER ROW METER

APPENDI X A

JULIAN DATE 209. 1986

 

 

0.30

 

 

 

 

 

"bfzmbfsmbfé"'iiimifimifimié' '25
TOMATO PLANTS PER Row METER

147‘

JULIAN DATE 216. 1986

 

 

 

 

 

 

: 0
E E 1.0-: o . Iq,
5 05-3
0.0: . . fl . .
OJ” 0J0 O10 0.30 0.00 0.30
autumn?)
g 0.4: .
I
i 3 -
0.2-1 I I
.1 : . 3
0'9: a "I "I"" I ' I 'I 'f"I' ' I " I
51' 1.5-'2 .
E 0.5-3
0.3:- ......

 

 

TOMATO PLANTS PER Row METER'

APPENDIX A

Table 1.

plant sample

obtained tron tour plants

ables are:

Julian

date,

per replicate {or nynpbs,

(I').

bean

1985 intercrop field study data. PLH nymph counts
represent an average per half
per treat-ent

plant,

per block.

per treatnent
Treat-ent,
Nynpb count,

 

193
193
193
193
193
193
193
193
193
193
193
193
193
193
193
193
193
193
193
193
198
198
198
198
198
198
198
198
198
198
198
198
198
198
198
198
198
198
198
198
203

0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00

1‘1waH1500NHbQNHbUNI—‘bWNHQUNwaNHBWNi-‘bwNwaNH

0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
4.35
0.00
0.00
0.00
0.00
0.00
0.00
0.00
9.12
0.00
9.12
0.00
0.00
0.95
0.00
0.00
0.00
2.40
0.00
0.00
3.51
0.00
0.00
3.51
0.00
0.00
0.00
0.00
7.92
0.00
0.00
0.00

12.47

.045
.061
.014
.040
.061
.007
.005
.012
.030
.021
.007
.036
.038
.012
.009
.025
.025
.019
.009
.037
.104
.128
.039
.105
.039
.060
.015
.053
.028
.013
.021
.051
.056
.031
.035
.090
.020
.012
.017
.056
.104

on a 10
Bean leaf area was
per block.
Block, Plants sa-plied

and Bean leaf area

APPENDIX A

203
203
203
203
203
203
203
203
203
203
203
203
203
203
203
203
203
203
203
207
207
207
207
207
207
207
207
207
207
207
207
207
207
207
207
207
207
207
207
210
210
210
210
210
210
210
210
210
210
210

0.00
0.00
0.00
0.35
0. 35
0. 35
0.35
0. 55
0. 55
0.55
0. 55
1.10
1.10
1.10
1.10
2. 20
2. 20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55

“NH-bUNHOQNHbWNPDUNwaNwaNI-ibWNwaNwaNwaNwaNI-‘bww

149

11.76
12.47
0.95
30.87
9.75
0.00
7.35
24. 51
0. 00
0. 00
0. 00
32.00
0.00
0.00
0.00
7.92
0.00
0.00
3.92
34.32
20.67
0.00
3.12
7.92
21.60
2.07
3.92
17.15
4.80
0.00
0.72
12.47
5.27
0.00
2.75
7. 35
0. 00
0. 00
5. 76
43.07
40.47
75.20
30.87
28.67
28.67
6.27
16.32
36.72
21.60
26.55

.128
.039
.105
.039
.060
.015
.053
.028
.013
.021
.051
.056
.031
.035
.090
.020
.012
.017
.056
.205
.071
.049
.081
.150
.107
.058
.076
.173
.054
.125
.214
.201
.049
.083
.108
.083
.060
.081
.254
.103
.036
.024
.041
.075
.054
.029
.038
.087
.027
.062

APPENDIX A

210
210
210
210
210
210
210
210
210
214
214
214
214
214
214
214
214
214
214
214
214
214
214
214
214
214
214
214
214
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
221

0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00

P.WNP.WNHbWNwaNHbWNI-‘ub“NHDUNHfiwNI-‘bwNwaNHbMNwaNI-‘b

150

1.47
18.00
44.40

6.80

5.76
24.51

6.27

0.72

0.15
75.20
30.87
36.72
37.95
75.20
28.67
32.00
14.72
27.60
23.52
22.55
14.72
37.95
22.55

9.75

7.35
23.52

9.12

4.80

2.40
124.2
16.32

99.4
27.60
168.5

0.95
11.76

4.35
109.8
15.12
13.22
22.53
33.65
26.25
18.72

4.90

7.23

4.13
20.02

0.00
107.7

.107
.100
.025
.041
.054
.041
.030
.040
.127
.157
.184
.093
.189
.118
.073
.129
.119
.042
.123
.121
.142
.113
.061
.048
.061
.101
.024
.025
.023
.157
.184
.093
.189
.118
.073
.129
.119
.042
.123
.121
.142
.113
.061
.048
.061
.101
.024
.025
.023
.350

APPENDIX A

221
221
221
221
221
221
221
221
221
221
221
221
221
221
221
221
221
221
221
224
224
224
224
224
224
224
224
224
224
224
224
224
224
224
224
224
224
224
224
228
228
228
228
228
228
228
228
228
228
228

0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55

WNHDNNwaNwaNI-‘bwNwaNwaNwaNHOWNI-‘b“NHbWNwaNwaN

151

29.76
47.12
41.76
114
30.87
55.76
27.60
28.67
7.35
10.40
27.60
48.51
18.87
10.40
17.15
4.80
22.55
4.80
19.76
116.2
33.15
89.76
18.00
71.76
16.32
32.00
19.76
37.95
5.27
24.51
18.00
32.00
18.87
3.92
11.76
27.60
14.72
7.35
7.35
76.95
45.75
52.80
30.87
37.95
18.87
7.35
17.15
15.51
8.51
14.72

.128
.193
.156
.147
.135
.190
.211
.176
.174
.139
.211
.153
.063
.035
.050
.045
.052
.029
.035
.350
.128
.193
.156
.147
.135
.190
.211
.176
.174
.139
.211
.153
.063
.035
.050
.045
.052
.029
.035
.219
.194
.345
.241
.336
.205
.177
.367
.363
.105
.198

APPENDIX A

228
228
228
228
228
228
228
228
228
232
232
232
232
232
232
232
232
232
232
232
232
232
232
232
232
232
232
232
232
239
239
239
239
239
239
239
239
239
239
239
239
239
239
239
239
239
239
239
239

0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20

DQNPDUNHh“NwaNI-‘DWNH-waO-‘DWNH‘WNH.WNwaNwaNwaNI-‘b

152

18.87
22.55
11.07
2.07
7.92
6.27
4.35
0.95
4.35
66.75
30.87
37.95
37.95
47.12
15.51
19.76
14.72
28.67
9.12
12.47
11.07
7.92
14.72
6.80
3.51
3.12
8.51
2.07
3.12
28.67
30.87
15.51
20.67
13.20
15.51
5.27
15.51
25.52
19.76
15.51
15.51
10.40
9.75
0.00
7.92
1.47
5.27
1.47
2.75

.373
.213
.087
.119
.176
.156
.067
.089
.070
.219
.194
.345
.241
.336
.205
.177
.367
.363
.105
.198
.373
.213
.087
.119
.176
.156
.067
.089
.070
.316
.323
.201
.297
.379
.289
.335
.239
.276
.267
.156
.087
.158
.099
.057
.134
.098
.099
.053
.053

 

APPENDIX A

Table 2.

plants

1088 intercrop field study data.
represent an average per three trifoliates
on 30 plants per treatment in each block.

area was obtained trom six

per

 

block. Variables are: Julian date, Treatment, Block, Plants

sampled per replicate tor nymphs, Average nymph count, and

average bean leaf area (m').
188 0.00 1 30 0.46 .017
188 0.00 2 30 1.92 .019
188 0.00 3 30 0.22 .024
188 0.00 4 30 1.15 .023
188 0.35 1 30 0.25 .019
188 0.35 2 30 0.88 .016
188 0.35 3 30 0.19 .016
188 0.35 4 30 0.48 .015
188 0.55 1 30 0.25 .014
188 0.55 2 30 0.27 .015
188 0.55 3 30 0.22 .020
188 0.55 4 30 0.68 .016
188 1.10 1 30 0.08 .012
188 1.10 2 30 0.48 .014
188 1.10 3 30 0.08 .018
188 1.10 4 30 0.75 .020
188 2.20 1 30 0.02 .015
188 2.20 2 30 0.58 .020
188 2.20 3 30 0.19 .020
188 2.20 4 30 0.79 .017
192 0.00 1 27 0.95 .017
192 0.00 2 30 1.34 .024
192 0.00 3 30 . .019
192 0.00 4 0 . .023
192 0.35 1 30 0.75 .019
192 0.35 2 30 0.19 .016
192 0.35 3 30 . .016
192 0.35 4 0 . .015
192 0.55 1 30 0.88 .014
192 0.55 2 30 0.51 .015
192 0.55 3 0 . .020
192 0.55 4 0 . .016
192 1.10 1 30 0.42 .012
192 1.10 2 30 0.42 .014
192 1.10 3 0 . .018
192 1.10 4 0 . .020
192 2.20 1 30 0.15 .015
192 2.20 2 25 0.58 .020
192 2.20 3 0 . .020
192 2.20 4 0 . .017
195 0.00 1 30 0.84 .051

PLH nymph counts
per plant,
Average bean leaf

treatment in each

APPENDIX A

195
195
195
195
195
195
195
195
195
195
195
195
195
195
195
195
195
195
195
202
202
202
202
202
202
202
202
202
202
202
202
202
202
202
202
202
202
202
202
205
205
205
205
205
205
205
205
205
205
205

0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55

“NH-bUNwaNwaNHbUNHDwNI-‘bwNHTLUNHbUNwaNHDwNwaNI-‘bwh’

154

0.42
0.11
0.25
0.64
0.05
0.08
0.19
0.11
0.98
0.11
0.22
0.02
0.34
0.11
0.15
0.15
0.15
0.15
0.11
2.14
0.95
2.58
1.31
2.20
0.42
0.72
0.79
0.64
0.34
0.98
0.88
0.64
0.05
0.64
0.56
0.56
0.34
0.81
0.25
2.17
2.17
1.80
3.16
1.89
1.71
0.79
1.18
1.00
1.20
0.81

.071
.084
.062
.061
.052
.038
.072
.023
.043
.047
.048
.020
.042
.044
.047
.031
.050
.058
.097
.128
.159
.182
.146
.124
.107
.083
.097
.065
.094
.116
.124
.086
.098
.066
.119
.057
.088
.082
.098
.128
.159
.182
.146
.124
.107
.083
.097
.065
.094
.116

APPENDIX A

205
205
205
205
205
205
205
205
205
209
209
209
209
209
209
209
209
209
209
209
209
209
209
209
209
209
209
209
209
216
216
216
216
216
216
216
216
216
216
216
216
216
216
216
216
216
216
216
216

0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20
0.00
0.00
0.00
0.00
0.35
0.35
0.35
0.35
0.55
0.55
0.55
0.55
1.10
1.10
1.10
1.10
2.20
2.20
2.20
2.20

.UNHDQNHQUNwaNwaND-‘b“NHQUNwaNfi-‘bwNwaNHDWNwaNF-‘b

155

1.31
0.68
0.64
0.64
1.00
0.81
0.98
0.56
1.05
1.80
1.20
2.20
1.10
1.15
0.75
1.05
0.81
0.79
0.62
0.75
1.05
0.25
0.11
0.48
0.84
0.81
0.19
0.95
0.48
2.83
1.45
3.16
1.26
1.47
1.42
1.10
0.88
0.91
1.08
0.79
1.08
0.81
0.51
1.05
1.42
0.84
0.46
0.88
0.34

.124
.086
.098
.066
.119
.057
.088
.082
.098
.238
.182
.238
.258
.232
.214
.176
.175
.139
.216
.192
.164
.101
.114
.191
.136
.080
.145
.156
.188
.397
.370
.505
.390
.385
.351
.311
.266
.113
.209
.272
.276
.111
.203
.215
.231
.137
.213
.235
.221

 

APPENDIX B

POTATO LEAFNOPPER BEHAVIOR STUDY

156

APPENDIX B

 

...mo.ovm «enu.pnuc
«v.elh_ «(>oz¢ aa31uco can :OqulMOuIIIMu «can unc.ovm.
accunuucoun 30: III) nuculuaouv Iootuon noncououuua
.nuIQIUIIMa Insanaumc can Inouucou IIoa Isa unclI
no>uou III: :0 use: gee-«nouns II no Icnuausc coax;xur.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

P p b b m P b D
IN
w
1¢
1. 1.
WT L J. T
:mer [I 1—1 #1 1.. [1 TD
.. b F .. 12
INF

 

 

 

SELLFINIW dO EBBWHN

APPENDIX B

Table

plant surface during the

study.

157

1. Mean number of minutes a leafhopper spent on each

15 min

small

A treatment contained two leaves.

cage, observation

 

IEEAIHENI

Bean (control 1)
Bean (control 2)
Bean/Tomato
Bean
Tomato
Tomato
Bean/Pepper
Bean
Pepper
Pepper
Bean/Corn
Bean
Corn
Corn
Bean/Squash
Bean
Squash
Squash
Bean/Radish
Bean
Radish
Radish
Bean/Cabbage
Bean
cabbage

cabbage

MEAN
7.7

a: HUI
O O O
N was

Nib
O O
15‘)

w H01
0 I
U" ON

N)
NW

N HUI
N O‘N

1.9

 

A total of 18 individual leafhoppers
each treatment.

were observed for

158

APPENDIX B

Table 2. Mean number of minutes during an arrestment bout

on bean leaves, for those treatments containing bean
bean controls, and bean/companion-leaf

treatment contained two leaves.

(i.e.

treatments). A

 

TREAIHENI

Bean (control 1)
Bean (control 2)
Bean/Tomato
Bean/Pepper
Bean/Corn
Bean/Squash
Bean/Radish

Bean/Cabbage

MEAN

8.3
9.2
8.8
8.9
9.3
9.0
7.9
6.9

5.8
6.6
5.9

 

An arrestment bout is the duration of time from arrival

on a surface to relocation upon another surface.

For each

treatment a total of 18 individual leafhoppers were observed
for 15 min within the small cages.