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EFFECTS OF WITHIN-FIELD LOCATION OF HOST PLANTS AND
INTERCROPPING ON THE DISTRIBUTION OF Microtheca ochroloma (Stil) IN
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
I would like to thank my committee members for their dedication and assistance
in this endeavor. In particular, I am grateful to Dr. Swisher for her overall guidance and
instruction in scientific method; to Dr. McSorley for his help with experimental design
and statistical analysis; and Dr. Webb for thoughtful and persistent editorial comments
and use of her lab facilities.
I would like to thank my family for their continuous love and support.
I would like to thank the Organic Farming Research Foundation for its generous
financial support for this project.
I would like to thank Rose Koenig for hours of grant writing assistance and her
and her family for use of their farm.
I would like to thank all the farmers in north central Florida who shared their
anecdotal evidence and keen observations with me, and whose experiences were the
impetus for this research.
I would like to thank my friends and colleagues at UDSA-ARS for their patience
and clarification of the finer points of entomology.
TABLE OF CONTENTS
A C K N O W L E D G M E N T S ................................................................ ......... .................. iii
LIST O F FIG U R E S .... .............................. ....................... ........ .. ............... vi
ABSTRACT ........ .............. ............. .. ...... .......... .......... vii
1 IN TR OD U CTION .................. ............................. ....... ...... .............. .
D description ofM ochrolom a ....................... ......... ......................... .. .............. 2
Characterization of M ochroloma in Florida ....................................... .............. 3
Pesticide Resistance and M ochroloma.................... ................................... 5
Organic Research and M ochroloma......... .............................................. .......... 6
R research O bjectiv es........... .................................................................. ...... ........... 6
2 LITER A TU R E R EV IEW ................................................................ ....................... 7
D orm ancy and Em ergence................. ............................ ....................... .............. 8
Host Plant Preferences: Searching and Finding................... .............. 13
Chrysomelid Habitats..... .......... ........ ................. ......... 13
Host Plant Finding in Simple and Complex Environments ................................. 14
H ost Plant Finding Theories .............. ......................................................... 17
H ost Plant Finding M echanism s ........................................ ......... .............. 23
Research Objectives and H ypotheses ........................................ ................. ...... 25
3 M E T H O D O L O G Y ............................................................................ ......................27
Border Versus Interior Experim ent ...................................................... ..... ... .. 27
Intercropping Experim ent .......... ..................................... ........ ... .............. 31
4 R E S U L T S ..................................................................3 3
Border Versus Interior Experiment................. ............... ................... 33
Intercropping Experim ent ......... .................................... ................................... 37
5 D ISC U S SIO N ...........................................................................40
Border Versus Interior Experiment................. ............... ................... 40
Intercropping Experim ent ......... .................................... ................................... 48
6 C O N CLU SIO N ............... ............................ ............ ............. ........ 54
R research Im plications .................. .................................. ....... .... ............ .. 54
D direction s for F uture Stu dy .......................................................................................... 54
L IST O F R EFE R E N C E S ............................................................................ ...............57
B IO G R A PH IC A L SK E T C H ...................................................................... ..................63
LIST OF FIGURES
1-1 Feeding damage to experimental plots of mizuna by M. ochroloma. .........................
1-2 An adult female M icrotheca ochroloma................................... ......................... 2
1-3 A second instar larva Microtheca ochroloma............... ....................3
3-1 Field layout for border versus interior experiment. The dashed lines represent rows
that were not part of the experiment, and the letters designate the experimental
plots of host plants at both ends of the rows.................................................29
4-1 Mean number of yellowmargined leaf beetles in border versus interior plots
according to life stage. ...................... .. .... ....................................... 33
4-2 Total number of yellowmargined leaf beetles collected from host plants. Plots A-F
are the interior plots; G-L are border plots. Note the different y-axis scales........35
4-3 Yellowmargined leaf beetle adult (AD), egg (EG) and larval (LA) distributions
during a one-w eek sam pling period ............................................ ............... 36
4-4 Mean number of yellowmargined leaf beetle eggs collected from experimental plots
based on the proximity of the plots to non-experimental host plants ..................37
4-5 Mean number of yellowmargined leaf beetles collected on intercropped host plants by
date and host plant density .................................. ............... ............... 38
4-6 Mean number of yellowmargined leaf beetles found on host plants...........................39
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science
EFFECTS OF WITHIN-FIELD LOCATION OF HOST PLANTS AND
INTERCROPPING ON THE DISTRIBUTION OF Microtheca ochroloma (Stil) IN
Chair: M.E. Swisher
Major Department: Natural Resources and Environment
The yellowmargined leaf beetle, Microtheca ochroloma (Stil), is a pest for
organic vegetable farmers in Florida. Very little is known about the ecology of M.
ochroloma. The yellowmargined leaf beetle is dormant during the warmest part of the
year, but it is not clear whether this dormancy constitutes aestivation or quiescence. In
field studies, populations of adult M. ochroloma were higher on host plants in the field
interior than on the field borders, indicating that border areas are not important dormancy
habitats. Microtheca ochroloma accumulated in monocropped plots of host plants in
larger numbers than in intercropped plots, but there was no difference in the number of
beetles per plant between the monocropped and intercropped treatments. Therefore,
intercropping does not appear to be a useful control strategy for this beetle by organic
farmers. The searching behavior of the yellowmargined leaf beetle appears to be density
dependent. Small populations of yellowmargined leaf beetles do not congregate or
engage in patch restricted searching. At higher population levels, M. ochroloma move en
masse in response to their own herbivory. More research on the host-plant finding
behavior and basic ecology ofM. ochroloma is necessary to develop control strategies
appropriate for organic farmers.
The yellowmargined leaf beetle, Microtheca ochroloma Stil, (Coleoptera:
Chrysomelidae) is a pest that devastates high value cruciferous crops, such as mizuna
(Brassica rapa, japonica group), mibuna (Brassica rapa, japonica group), napa cabbage
(Brassica rapa, pekinensis group), turnip (Brassica rapa), mustard (Brassicajuncea),
and watercress (Nasturtium officinale) (Figure 1-1).
Figure 1-1 Feeding damage to experimental plots of mizuna by M. ochroloma
Microtheca ochroloma feeds on these cruciferous host plants, whose primary
allelochemical is mustard oil glucosides (Hicks 1974). Jolivet and Hawkeswood (1995)
comment that adults of the genus Microtheca can feed on the pollen of plants in the
Rosaceae family. No reports ofM ochroloma feeding on non-crucifers have been made.
Microtheca ochroloma is widespread throughout much of the southeastern Gulf States.
The yellowmargined leaf beetle was first identified in the United States in Mobile,
Alabama, in 1947 (Chamberlin and Tippins 1948). The yellowmargined leaf beetle was
subsequently found in Louisiana, Texas, Mississippi, and Florida. In 1994, M.
ochroloma was collected in North Carolina (Staines 1999). The yellowmargined leaf
beetle is native to South America, where it is found in Argentina, Brazil, Chile and
Uruguay (Woodruff 1974).
Description ofM. ochroloma
The yellowmargined leaf beetle is about 5 mm long (Woodruff 1974), with
females generally larger than males. Microtheca ochroloma is dark brown, bronze or
black, and has orange, yellow or white margins around its elytra (Woodruff 1974). Each
elytron has four prominent rows of punctures (Figure 1-2).
Figure 1-2 An adult male icrotheca ochroloma
Figure 1-2 An adult male Microtheca ochroloma
Female M. ochroloma deposit bright orange, elongate eggs on plant stems, under
fallen leaves or on the soil surface. Eggs are commonly laid in small clutches but may be
found singly. Larvae range in color from grayish to yellow-brown and have a sclerotized
head capsule (Figure 1-3).
Figure 1-3 Second instar larvae of Microtheca ochroloma
According to Oliver and Chapin (1983), there are three larval instars. Jolivet and
Hawkeswood (1995) refer to the pre-pupa stage as the fourth instar. Pupal cases are dark
brown or black and may be found attached to the undersides of leaves or on the soil
surface. Development ofM. ochroloma from egg to adult takes about 23 days (Oliver
and Chapin 1983).
Characterization ofM. ochroloma in Florida
In 2001, farmers in Florida reported infestations ofM ochroloma as far north as
Jefferson and Leon counties (George and Margie Cole, pers com.) and as far south as
Charlotte County (David Coles, pers com.). Farmers have reported changing their
growing practices due to the severity of yellowmargined leaf beetle infestations (Joe
Durando and Charley Andrews, pers com.). Changes reported include not growing
susceptible crops at all or decreasing the proportion of susceptible crops grown. Large
field populations of this foliage-feeding insect cause significant economic losses to
There are three reasons why M. ochroloma causes such problems in Florida. M.
ochroloma's cruciferous host plants thrive in the cool months from October to April that
comprise most of the growing season for organic vegetable farmers here. During these
months, hard frosts or freezes are relatively rare. As a result, the adult beetles continue to
feed and reproduce throughout the winter, although larvae are somewhat more
susceptible to cold weather. The abundant food supply and above-freezing temperatures
create ideal conditions for the yellowmargined leaf beetle. Finally, the yellowmargined
leaf beetle is an introduced pest and has no known predators or parasites in the United
States. Freed from bio-regulatory interactions, M. ochroloma has the potential to spread
unchecked. It appears to migrate at a slow rate, which may have thus far prevented it
from becoming a nuisance on the order of such introduced pests as whitefly (Bemisia
spp.), imported fire ants (Solenopsis invicta), diamondback moth (Plutella xylostella) and
In Florida, M. ochroloma is part of an invasion of adventive species. Florida is
particularly susceptible to the threat of non-native species because of its tropical to sub-
tropical climate, its insularity and fragmented natural habitat (Simberloff 1997). There
are nearly a thousand non-native insect species in Florida (Frank et al. 1997). Experts
estimate that one major new pest arrives every year (Frank et al. 1997).
Pesticide Resistance and M. ochroloma
Little research has been done on the biology or ecology of M. ochroloma because
the application of broad-spectrum synthetic insecticides has provided sufficient control
for conventional growers. However, the use of insecticides on a large scale will speed up
the selection process for individuals with pesticide resistance, as demonstrated by the
development of resistance in such pests as Colorado potato beetle (Leptinotarsa
decemlineata) and tobacco budworm (Heliothis virescens). Resistance to insecticides has
been reported since the early 20th century, with 447 species of insects and mites resistant
to at least one insecticide (Georghiou 1986). Of these resistant insects, 66 species are
Coleopterans. Follett and Roderick (1996) list 15 species of chrysomelids that have
developed insecticide resistance worldwide. Overall, 59% of the species with known
resistance are described as "agriculturally important" pests (Georghiou 1986). The
economic costs of resistance are staggering.
The emergence of chemical resistance in M ochroloma will eventually
necessitate control measures that are based on an understanding of insect ecology. Many
of the newer, reduced-risk insecticides act against a narrower range of pests, but few of
these target beetles. If ecological methods can be developed to control M ochroloma,
farmers would be able to use these reduced-risk chemicals against aphids and various
lepidopteran pests. Currently, with neither the knowledge about its ecology nor the
option to use chemical means for its control, organic farmers have been the most affected
by this pest (Rose Koenig, pers. comm.).
Organic Research and M. ochroloma
This project is a needed addition to the small number of organic and on-farm
research projects carried out in the United States southeast region (which includes
Florida, Georgia, Alabama, Mississippi, Louisiana, South Carolina, and North Carolina).
Florida is the second leading state in the country in vegetable production in the United
States, with $6.95 billion in cash receipts in 2001 (National Agriculture Statistics Service
2002). However, as of 2001, the state had no certified organic research acreage (Sooby
2001). In Florida, only three on-farm research projects have been conducted with the
input of certified organic farmers (Sooby 2001). This situation is reflected nationwide as
well. Sales of organic products topped $9 billion in 2001, or about 2% of total market for
agricultural products. Publicly funded organic agriculture research comprises only about
0.1% of total agriculture research funding (Lipson 1997).
This study will describe aspects of emergence and host finding behavior by the
yellowmargined leaf beetle and evaluate whether intercropping can be employed by
farmers to reduce the severity of beetle outbreaks.
In studying the effect of photoperiod on M. ochroloma, Oliver and Chapin (1983)
asserted that yellowmargined leaf beetles are multivoltine, with adults entering
aestivation from mid-June to October in Louisiana. However, they report finding M.
ochroloma in ground trash as early as September. They theorized that the ability of M
ochroloma to develop continuously in the laboratory (at ca. 27 C) under an ambient
photoperiod indicates that temperature is important in mediating diapause. Oliver and
Chapin (1983) did not rear yellowmargined leaf beetles at outdoor ambient temperatures,
or vary temperature with photoperiod in order to test this assertion.
In efforts to clarify the aestival behavior of the yellowmargined leaf beetle, I
sampled an organic farm in Gainesville, Florida on 1 July 2001. I found a dozen adult
yellowmargined leaf beetles on turnip greens. I did not find any eggs or larvae. I took the
adult beetles and exposed them to a 14:10 photoperiod and approximately 250 C. The
beetles began to mate within 24 hours and oviposition soon followed (Bowers,
There are several possible explanations for the disappearance ofM. ochroloma
during the summer. The dormancy pattern of the yellowmargined leaf beetle has not
been well described. Pinpointing when and where the yellowmargined leaf beetle
emerges and characterizing its host-finding patterns after emergence are the first steps in
developing ecologically-based control strategies.
Dormancy and Emergence
The general term dormancy encompasses two distinct types of insect behaviors:
diapause and quiescence. Diapause refers to a resting period that is pre-programmed and
may be mediated by environmental factors, but is not caused directly by them (Danks
1987). The cues that signal diapause do not limit an insect's development per se, but
rather act to set off a series of neuro-hormonal responses known as diapause induction
(Danks 1987). Before an aestivating insect can resume activity it must complete the
diapause development, a period which restores the ability of an insect to respond to
favorable conditions (Danks 1987). A diapausing insect cannot respond to favorable
conditions which resume before diapause development is completed. Similarly, Masaki
(1980, p.3) comments that aestivation is not only a pattern of dormancy during the
summer, but that "there should always be a particular response to environment or
programmed sequence of physiological events to complete the dormant stage after the
Quiescence is a dormancy that is a direct response to environmental thresholds
(e.g., not enough food, temperature extremes approaching lethal limits) (Danks 1987).
Quiescence does not involve the same series of pre-programmed developmental stages
involved in diapause, so quiescent insects can resume normal activity as soon as
environmental conditions become favorable.
Photoperiod and temperature are often cited as diapause cues, while food quality
and quantity are said to provoke quiescence or contribute to diapause in an indirect way.
The overlap of these factors and the degree with which they interact are responsible for
many of the insect dormancy strategies observed in the field. There are a great number of
interactions that control diapause induction.
Photoperiod is the most reliable and easily identifiable diapause cue in temperate
climates and terrestrial habitats (Danks 1987). Insect diapause is frequently induced by
photoperiods above or below some threshold value, known as the critical photoperiod.
The critical photoperiod is the photoperiod under which half of a group of individuals
enter diapause (Danks 1987). Insects that respond to long days with diapause (i.e. they
diapause in the summer) are known as short-day insects. Long-day insects are those that
require long days for their active stages and are cued to diapause by short days.
Although seasonal variations in temperature are predictable, variation in
temperature from one day to the next can be drastic. For this reason, temperature is not
considered an effective diapause cue, except in a limited number of insects. However,
the interaction between temperature and photoperiod plays a fundamental role in
mediating diapause (Danks 1987). Temperature can affect photoperiod in several
different ways. In some cases, insects are only sensitive to photoperiod cues between
certain temperatures. In other insects, low temperatures can strengthen the effect of short
days on diapause induction in long-day insects (Danks 1987). Long photoperiods are the
cue for summer diapause, or aestivation (Masaki 1980). In general, high temperatures act
in concert with long photoperiods in summer diapause induction. The onset of lower
temperatures is favorable for diapause development and termination (Masaki 1980).
Although relatively little has been written on the subject, summer diapause is more
common in insects than the literature might suggest (Masaki 1980). The relationship
between temperature and photoperiod in signaling insect diapause is not straightforward,
however, as temperatures alone can induce aestivation in the cabbage root fly, Delia
radicum pupae (Finch and Collier 1985).
In addition to photoperiod and temperature, food plants can influence dormancy
in phytophagous insects. Seasonal changes influence the availability of food plants which
can have distinct effects on quiescence and diapause. First, lack of food is a direct
control (rather than a cue) that causes quiescence (Danks 1987). Secondly, the
unavailability of host plants may slow an herbivore's development, exposing the insect to
diapause inducing conditions for a longer period of time. This is considered and indirect
effect (Danks 1987). Both type and quantity of food can alter an insect's developmental
sequence, although the presence or absence of particular food plants is a more reliable
cue for monophagous than polyphagous insects (Danks 1987). For the Colorado potato
beetle, photoperiod and temperature are the major inductive cues, but access to food
plants during long days ensures that beetles do not enter diapause (De Wilde et al. 1959).
Oliver and Chapin (1983) do not discuss the influence of altered habitat or food resources
as a possible explanation for dormancy in M. ochroloma.
Most species can enter diapause only in a single specific life cycle stage,
according to taxonomic group but two or more dormant stages are possible within diverse
groups (Danks 1987). Temperate region chrysomelids were reported to enter diapause as
adults (Krause 1982 from Danks 1987), although a few species diapause as eggs, and
some genera as larva. A survey of the distribution of summer diapause by stage shows
that Coleopterans most often enter summer diapause as adults (38 out of 44 species
surveyed) (Masaki 1980). The protection offered by the adult beetles' sclerotized cuticle
as well as its ability to move to more favorable microclimates afford adult beetles the best
chance for survival during aestivation (Masaki 1980). Oliver and Chapin (1983) report
that the yellowmargined leaf beetle enters diapause as an adult, but this observation has
not been substantiated. The adult yellowmargined leaf beetles are the only ones to be
seen in the field during the summer and the first to return in the fall, so it seems likely
that this is the oversummering stage (Bowers, unpublished). Adult diapause involves the
cessation of post-emergence ovarian development. The dormant sub-stage is the newly
emerged, non-parous adults (Danks 1987). Oliver and Chapin (1983) do not discuss the
possibility of a reproductive diapause as an explanation for the yellowmargined leaf
beetle's scarcity during the summer months.
Both summer and winter diapausing insects exhibit the same pre-dormancy
behaviors, including seeking shelters, migrating from feeding/ breeding sights and
burrowing in the soil (Masaki 1980). Insects may travel between crop plants and non-
agricultural landscapes for a number of reasons including changes in food availability,
habitat disturbances and natural dispersal patterns (Altieri 1994). Weedy field borders
can harbor insect pests until field conditions are appropriate for their return to agricultural
hosts (Altieri 1994), particularly when the weeds are closely related to agricultural plants.
Insects display as many variations in diapause habitat as they do in diapause
timing. Bean leaf beetles, Cerotoma trifurcate (Forster), leave feeding sites for field
margins, where they spend their reproductive diapause (Boiteau et al. 1979a). Upon
emergence, adult Colorado potato beetles can fly or walk back to known feeding sites
from overwintering sites, or they may migrate long distances to new feeding sites. For
second generation Colorado potato beetles, the usual pattern is to diapause in the field or
travel short distances to field margins for overwintering (Voss and Ferro 1990).
In the spring, newly emerged Colorado potato beetle females may oviposit briefly
before diapausing or may continue to reproduce without entering diapause. Their
progeny will remain active during the summer months and enter diapause in the fall. The
activity of the second generation in the field during the spring and summer tends to
obscure the aestival habits of the first generation adults (Tauber et al. 1988). Tauber et
al. 1988 found that the variability in summer oviposition (and subsequent active summer
populations) was largely due to temperature and food variability.
Oliver and Chapin (1983) observe that yellowmargined leaf beetle populations
drop off dramatically in the hot summer months and attribute this decline in activity to
aestivation. Since M. ochroloma did not enter dormancy at all under long photoperiod
and constant temperature regime in their laboratory, the dormancy ofM. ochroloma may
be mediated by a combination of photoperiod and temperature. It is also possible that the
yellowmargined leaf beetle experiences a quiescence during the summer months. Unlike
diapause, quiescence is a direct and immediate dormancy response to altered
Masaki (1980) proposes that summer diapause comprises part of a polymodal
emergence strategy by adult insects, whereby a few insects continue to develop and
oviposit on a limited basis while others enter dormancy. Multiple diapause responses in a
single population would ensure survival during adverse environmental conditions
(through the dormancy strategy) while a few insects reproduce, which keeps the
population active and growing on a limited basis. If there is no strong selective pressure
towards one or the other of these strategies, both will continue to persist in the
population. This is a third aestival pattern that could describe the yellowmargined leaf
In summary, the stage during which diapause induction takes place is highly
variable in insects. It can occur as a complete halting of activity in immatures or as the
reproductive diapause of adults. Induction cues also vary at the species level and may be
the result of unfavorable food or climatic conditions, most often photoperiod,
temperature, or the interaction of temperature and photoperiod. Diapause can also vary
within a species according to geographical distribution. The induction signals and
variability of diapause response in M. ochroloma are unknown. It is not yet clear which
inductive cues are responsible for dormancy in M. ochroloma, or where M ochroloma
spends its dormant period.
Host Plant Preferences: Searching and Finding
Ameen and Story (1997a) established that first-instar yellowmargined leaf beetles
preferred turnips to other cruciferous vegetation, third instars preferred turnip and
mustard greens, while adults consumed turnips, mustard, and radish in equal quantities.
Chamberlin and Tippins (1948) Haeussler (1951), Oliver (1956), Spink (1959) all
reported that the yellowmargined leaf beetles were found more frequently on their
preferred host plants in the field (turnip and mustard) than other crucifers, although this
phenomenon has never been quantified. Generally, females of phytophagous insects are
able to choose host plants based on characteristics associated with reproductive
performance, so that host preference and fecundity are expected to be correlated
(Ferguson et al. 1991, Ramnath et al. 1992). Collard and cabbage were the least
preferred host plants of the beetles. In the field, M. ochroloma exhibited these same
preferences, feeding on cabbage only when no other host plants were available
(Chamberlin and Tippins 1948). Cabbage plantings adjacent to a field of turnips heavily
infested with yellowmargined leaf beetles did not become infested with beetles
(Chamberlin and Tippins 1948). Ameen and Story (1997) postulate that the texture of
host plant leaves may influence feeding; the beetles avoid plants with tough or waxy
When a female insect locates an appropriate oviposition habitat, her progeny may
find the habitat suitable as well. Lower dispersal rates are generally associated with more
specialized phytophagous species (Stinner et al. 1983 from Nielsen 1988). Chrysomelids
commonly exhibit this phenomenon. For many chrysomelids, mating, oviposition, and
adult and larval feeding all take place on the same plant species (Nielsen 1988). Larvae
may complete their development on plants only meters away from those that supported
their parents' own development (Carne 1966 from Nielsen 1988).
Host Plant Finding in Simple and Complex Environments
While life history characteristics such as monophagy, shared adult and larval
resources, and the potential for low dispersal rates all strengthen the relationship between
host and insect (Strauss 1988), it is not known exactly how herbivores initially find their
preferred host plants. Generally, insects rely on visual, mechanical, and chemical stimuli
to locate potential host plants and to determine their acceptability for feeding and
oviposition. While insects generally respond to evidence of general habitat like yellow-
green reflected light, monophagous herbivores rely on additional, more specific host
plant cues (Stanton 1983). Host plant finding is influenced by background vegetation
(e.g. an adjacent meadow or forest) as well as the distribution of cultivated host and non-
host plants, as in an agricultural intercropping pattern. Generally, it is thought that a
habitat composed of varied microclimatic, biotic and structural elements supports a
greater stability in insect pest populations (Altieri 1994).
While investigating the arthropod community of Brassica oleracea, Pimentel
(1961) found more herbivores residing in dense host plantings than sparse ones, but host
plants in more sparse areas had more herbivores per plant. Herbivores tended to spread
themselves out in a dense habitat, so that each plant is less likely to be chosen by an
individual herbivore (Pimentel 1961). Dense habitats tended to support fewer taxa
overall than the sparse plantings (Pimentel 1961). Also, smaller sized plants spaced far
apart were more difficult for herbivores to locate, but once the plants grew larger, they
became easier to find, which increased the tendency toward aggregation among the
insects (Pimentel 1961).
Dempster (1969) found that crucifers grown in a weedy environment had fewer
cabbage butterflies, Pieris rapae, than those grown without weeds. Both Phyllotreta
striolata and Phyllotreta cruciferae were found more commonly in the cultivated
(weeded) plots than the uncultivated ones, where they were all but absent (Cromartie
1975). Host collards intercropped with tomato and tobacco (Nicotiana tabacum) had
lower colonization by flea beetles, less leaf damage due to beetle feeding, and lower
emergence of subsequent generations (Tahvanainen and Root 1972). There were fewer
striped cucumber beetles, Acalymma vittata, in polycultures than in cucumber
monocultures, even taking into account the smaller plant size in the polyculture plots
(Bach 1980). In a similar set of experiments, Bach (1980) found that increasing the
cucumber stand purity increased the beetle density per plant. Additionally, the striped
cucumber beetle, A. vittata preferred cucumber leaves grown in monocultures over those
grown with tomato plants (Bach 1980).
Risch (1981) studied several species of beetles (Chrysomelidae: Galerucinae) and
found that monocultures had higher numbers of beetles than polycultures, with no
significant differences between predation or parasitism between the polyculture and
monoculture treatments. Purposeful cultivation of crucifers and non-host plants together
in an intercropping system reduced populations of flea beetles, Phyllotreta crucifera, in
broccoli (Garcia and Altieri 1992).
During the first two seasons of their study, Latheef et al. (1984) found no
differences in populations ofPhyllotreta cruciferae between monocultures of collards
(Brassica oleraceae) and polycultures of collards with non-cruciferous vegetables. The
third season, the populations of P.cruciferae was smaller on intercropped collards than
monocultures. The monocultures also had higher plant damage than the polycultures
during the third season. The overall populations of P. cruciferae were much higher the
first two seasons than the third, and the authors posit that the polyculture did not provide
protection to the host plants in the face of much higher populations of flea beetles.
The effects of vegetationally diverse plantings on insect population distribution
are far from predictable. Andow (1991) analyzed literature on both additive and
substitutive polyculture plantings (a total of 209 studies involving 287 herbivores) and
found that just over half (51.9%) of the herbivores studied had lower population densities
in polycultures, and 15.2% had higher densities. Andow (1991) concludes that
polycultures are likely to support lower individual species densities than monocultures,
especially for monophagous insects. However, the range of arthropod responses to plants
and the mechanisms responsible for those responses are so varied that generalization is
not useful for pest management purposes. Smith and McSorley (2000) concur, observing
that the specific conditions under which polyculture can facilitate pest management or
even reduce chemical pest control applications must be tested more rigorously through
Host Plant Finding Theories
Cromartie (1975) found that Phyllotreta striolata and Phyllotreta cruciferae were
more frequent as plot size increased. Kareiva (1983) also found that densities of these
two species of flea beetles (P. striolata and P. cruciferae) increased with patch size.
Pieris rapae, on the other hand, appeared less frequently with increasing plot size
The theory of island biogeography (MacArthur and Wilson 1967) suggests that a
number of factors, including island size, determine how many species an island can
support. Generally, larger islands are able to support larger animal populations than
smaller islands. Larger islands are easier for individuals of a species to colonize and once
there, those individuals are less likely to leave or die out. Several authors, including
Janzen (1968) have suggested that the theory of island biogeography is applicable to host
plant finding by insects. Patches of host plants are "islands" among a sea of vegetation to
an insect. Janzen (1968) theorized that the number of herbivores is dependent on the size
and location of the host plant relative to adjacent vegetation, the similarity of the host
plant to that adjacent vegetation, the abundance of the plant in space and the relative
insect population on adjacent plants. The insect population in a host plant patch reflects
the equilibrium between herbivore emigration and immigration (or colonization in
biogeography terms). Janzen (1968) describes this relationship as a co-evolutionary one.
A theory of chemical coevolution between plants and insects was described by
Ehrlich and Raven (1964). Although acknowledging that plant mechanical defenses and
ecological considerations are valid parameters within which insects must operate when
choosing suitable host plants, Ehrlich and Raven (1964) conclude that it is secondary
chemical substances that largely dictate the patterns of herbivory observed in nature.
Even so, they caution that experimental verification is required to assess whether or not a
particular secondary chemical is an attractant of a feeding stimulant to a specific insect
(Ehrlich and Raven 1964).
Subsequent authors have agreed that chemical communication between plant and
insect is a key factor with regard to the feeding behavior of phytophagous insects
(Matsuda 1988). The relationships between cruciferous plants and crucifer feeding
insects illustrate this phenomenon. When crucifers are damaged, enzymes and
glucosinolates that are normally stored in different compartments of the plant cells (Luthy
and Matile 1984 from Nielsen 1988) are mixed and hydrolysis products (known as
mustard oils) are released (Stanton 1983). Glucosinolates and their hydrolysis products
are defensive products and are toxic to bacteria, fungi and a number of phytophagous
insects (Nielsen 1988). However, glucosinolates and mustard oils act as allelochemicals
to some insects, including crucifer-feeding chrysomelid beetles (Stanton 1983, Nielsen
1988). These compounds allow the beetles to distinguish a crucifer host plant from a
non-suitable plant (Nielsen 1988). Hawkes and Coaker (1979) established that the
cabbage root fly (Delia radicum) oriented towards host plant odors even in the absence of
visual or tactile cues. The production of plant volatiles can be positively correlated with
the density of herbivores feeding on the plant, resulting in aggregated feeding behavior
(Dicke and Vet 1999). Ameen and Story (1997b) did not compare the differences in
chemical attractants produced by their experimental host plants nor propose how
differences in chemical profiles may have influenced feeding by M. ochroloma.
Finch and Collier (2000) summarize a number of prominent theories that attempt
to explain how non-host plants interfere with host plant finding. These hypotheses
include physical or visual disruption of the host plant architecture, chemical "masking" of
host plant odors or production of chemical repellants, influencing host plant physiology,
and Root's (1973) resource concentration hypothesis and natural enemies hypothesis.
Despite the plethora of attention devoted to the topic of host plant finding, no single
theory has yet been able to explain the diversity of host plant finding behavior evidenced
by phytophagous insects.
In choice experiments, Tahvanainen and Root (1972) showed that the flea beetle
preferred the collard leaves alone to combinations of collard with tomato and collard with
ragweed (Ambrosia artemisiifolia). They suggest this is because non-host plant chemical
stimuli can dilute or mask chemical signals from host plants. Even when non-host plant
leaves were buried, the olfactory cues alone were enough to repulse beetles, especially
when the non-host plant was ragweed.
Non-host plant compounds in a more vegetationally complex environment may
amplify the effect of distance, further masking or overpowering host plant finding cues.
Non-olfactory components of a complex system may also factor into an insect's host-
finding efficacy. Insects seeking out a favorable microclimate will be further disoriented
by the heterogeneous temperature, light and moisture gradients available among a non-
cultivated plant community. In addition to the chemical defenses possessed by a single
plant, plants in a complex environment benefit from the variability in these factors. The
additional protection afforded to a single plant by complex surroundings was termed
associationall resistance" by Tahvanainen and Root (1972).
One of the most influential theories was the resource concentration hypothesis
proposed by Root (1973). Root (1973) found that the herbivore load (defined as the
biomass of herbivores per 100 g of dried foliage) was higher in pure stands than in
perimeter rows, but that the perimeter rows had greater herbivore diversity and evenness
than the pure stands. He proposed the resource hypothesis to explain the behaviors he
observed in the field.
Root (1973) theorized that species will tend to stay in an area of suitable host
plants. If a clump of host plants is favorable for the growth and development of a
phytophagous insect, individuals of that species will tend to accumulate on or around that
host plant. The more of the insect's life cycle requirements that are met by this habitat,
the more likely it is to remain there, and the longer the length of its stay will be.
Generalist herbivores or those that have varying habitat or food requirement throughout
their life cycle will tend to move among different host plants, rather than linger on one
plant. The end result is that specialized herbivores tend to accumulate in pure stands of
their host plants, and herbivores with generalized feeding patterns will move in and out of
a stand. The accumulation of specialized herbivores may be enough to produce an
overall higher herbivore load in pure stands (Root 1973). Root's resource concentration
hypothesis is complementary to the island biogeography model in predicting that
herbivore abundance should be positively correlated with host plant patch size.
Additionally, Root (1973) found that crucifer-specialist herbivores with the
narrowest host plant ranges (the flea beetle Phyllotreta cruciferae and the aphid
Brevicoryne brassicae) appeared at significantly higher densities in the pure stands. The
other crucifer specialists in this community, including the diamondback moth, Plutella
maculipennis, the flea beetle, Phyllotreta striolata, and the cabbage butterfly, Pieris
rapae, were found on the perimeter rows and even feeding on wild crucifers around the
perimeter. In both perimeter rows and in pure stands, herbivore load was positively
correlated to the P. cruciferae population and species diversity was inversely correlated
to P. cruciferae populations. Root's observation that other crucifer aphids emigrated
from host plants that had been damaged by P. cruciferae suggests that interspecific
competition reinforced the dominance of this flea beetle in pure stands.
Root (1973) offered the natural enemies hypothesis in addition to the resource
concentration hypothesis in order to explain his results. Root theorized that because
diverse vegetation provides more habitat niches and food resources for a greater number
of herbivores, it also supports more predators and parasites. Habitats that support an
abundance of natural enemies keep herbivore populations in check, so one or two species
don't dominate the community structure.
Root (1973) found that the diversity of predators and parasitoids was higher in the
pure stands than the perimeter on several occasions. Although the herbivore-to-predator
ratio of the perimeter rows was generally higher than that of the pure stand, the predators'
main prey were insects that made a small contribution to the herbivore load (early instar
strip feeders and sap feeders). Adult flea beetles were the most prevalent component of
this group, but are not predated upon and have only one specialized parasitoid. Thus, the
natural enemies hypothesis could not completely account for the lower herbivore loads in
the perimeter rows. According to Root, insects congregated in areas dominated by their
host plants and at the same time the wide variety of natural enemies which accumulated
in diverse vegetation controlled and evened out herbivore populations outside the pure
stands. Natural enemies and resource concentration work in a complementary fashion to
produce the distribution of insects observed by Root (1973).
Within the crucifer-arthropod community characterized by Root (1973), each
species preferred slightly different host plant dispersion characteristics. No single species
dominated all plant densities or both cultivated and uncultivated treatments. Root (1973)
concluded that while reduction of host plant density or intercropping may be effective in
controlling some insect outbreaks, host plant resistance, predation, and parasitism and the
timing of insect and host plant lifecycles were important factors in determining the
severity of herbivore loads on vegetation.
Coll and Botrell (1994) found that tall varieties of corn (Zea mays) intercropped
with beans (Phaseolus vulgaris) prevented colonization by adult Mexican bean beetles,
Epilachna varicestis. These tall corn-bean intercrop plantings had lower overall beetle
densities than bean monocultures or short corn-bean intercrops. Ostensibly, the tall corn
physically disrupted the searching pattern ofE. varicestis. Despite the adults' difficulty
in locating the beans among the tall corn, E. varicestis larvae developed more quickly on
tall corn-bean intercrop plots. In choice tests, E. varivestis preferred beans grown with
tall corn over the other bean leaves (Coll and Botrell 1994). The overall E. varicestis
density was higher in the monocropped plots, even taking into account the faster larval
development in the tall corn intercropped plots. Coll and Botrell's (1994) finding (that E.
varicestis preferred the beans grown with tall corn) does not fit with the associational
resistance of Tahvanainen and Root (1972). However, the density of E. varicestis does
support Root's (1973) resource concentration hypothesis. At the same time, the authors
observe that the population of natural enemies did not differ among the treatments and
that the overall mortality due to predation was low and did not differ among the habitats
(Coll and Botrell 1994).
Host Plant Finding Mechanisms
Taken together, the various theories of host plant finding explain the distribution
of insects observed in the field but offer little insight into the how herbivores find their
hosts. What are the mechanisms or behaviors involved in host plant finding?
Root (1973) predicted that altering the concentration of resources shifted the emigration-
immigration balance, thus accounting for the variation in herbivore densities. As
predicted by island biogeography and resource concentration hypotheses, Karevia (1983)
found increasing flea beetle densities with larger patch sizes. Large patches had more
beetles, regardless of the initial number of beetles placed in the patch, indicating that
emigration was more sensitive to patch size than immigration (Karevia 1983). Garcia
and Altieri (1992) observed that broccoli monocultures had more flea beetles than
intercopped plots. They also demonstrated that even when Phyllotreta cruciferae were
introduced into the monoculture and intercropped plots in equal numbers, the flea beetles
left mixed croppings of broccoli and vetch in vast numbers. Within 24 hours, the flea
beetle populations in the monoculture versus the vetch intercrop were similar to what
they had been before the experiment (Garcia and Altieri 1992).
These findings support Andow's (1991) assertion that insects spend less time in
patches of diverse vegetation and move more quickly than in monoculture plots.
Similarly, Hawkes and Coaker (1976) showed that although cabbage root flies (Delia
brassicae) laid fewer eggs on host plants that were intercropped with clover than those in
monoculture, D. brassicae found the host plants in equal numbers in polyculture and
monoculture. The clover did not hide the host plants. Instead the presence of the non-
host plants increased D. brassicae 's movements within the plots, resulting in less time
spent laying eggs and fewer eggs laid (Hawkes and Coaker 1979).
On the other hand, Stanton (1983) attributed herbivore concentrations to
herbivore population growth within a colonized host plant patch as well as the
emigration/immigration balance. A slightly different explanation was offered by Matter
(1997) for the distribution of the red milkweed beetle Tetraopes tetraophthalmus. Matter
(1997) observed that T tetraophthalmus' density did increase with patch size, but not due
to inter-patch migration. In fact, Matter (1997) found that female T. tetraophthalmus
tended to migrate to smaller patches of host plants. Distribution and density patterns of
T. tetraophthalmus were due to local reproduction and patch residence time. Matter
(1997) points out that larger patches provide more suitable oviposition sites, more
abundant food (which could produce larger and more fecund females) and decreased
mate searching time in patches with large numbers of beetles.
Risch (1981) studied various species of chrysomelid beetles (Acalymaa thiemei
(Baly), Ceratoma ruficornis rogersi, Diabrotica viridula (Fab.), Paranapiacaba
waterhousei (Jacoby), Diabrotica balteata (Le Conte) and Diabrotica adelpha (Harold)
and examined their patterns of movement after landing on a potential host plant. As with
other authors, Risch found that beetles left non-host plants more quickly than host plants,
resulting in increased movement in polyculture plots. Emigration from plots as well as
movement within plots were both higher in polyculture than in monoculture plots. Risch
(1981) observed that these patterns were due to the presence of corn in the intercropped
plots. The beetles avoided host plants that were shaded by the corn and the corn also
appeared to interfere with the beetle's flight patterns (Risch 1981).
Research Objectives and Hypotheses
There were three objectives of this research. The first objective was to determine
if yellowmargined leaf beetles remained active into summer if crucifers are present under
field conditions. Oliver and Chapin (1983) report that M ochroloma enters aestivation
from mid-June to October. The authors did not distinguish between aestivation (a
diapause response) and quiescence caused directly by unfavorable resource or climatic
conditions. I hypothesized that if the yellowmargined leaf beetle exhibited a pre-
programmed diapause response, the beetles would not be apparent, even when food was
The second objective was to determine if initial infestations ofM. ochroloma
arise from within the field, or from field edges. Oliver and Chapin's (1983) observations
that beetles can be found as early as 9 September in ground trash but not until a month
later in the field implies that they may oversummer outside agricultural fields in the
summer months and return during the autumn planting. I hypothesized that M ochroloma
infestations would arise first in areas closest to the oversummering location of the beetles.
If beetles oversummered in field edges, then host plants on the borders of the field would
be more rapidly infested than those host plants on the field interior.
The third objective was to determine if intercropping host plants with non-host
plants would protect the host plants from beetle infestation. I hypothesized that host
plants that were intercropped in low densities among non-host plants would be less
"visible" to M ochroloma, and thus less susceptible to infestations. The second part of
this hypothesis was that locating host plants in experimental plots near non-experimental
host plants would create a larger island of host plants. Microtheca ochroloma would
either already be present in the established non-experimental plots of host plants or more
quickly find the areas with experimental and non-experimental plots in close proximity.
Therefore, Microtheca ochroloma would be more abundant in the experimental plots
close to other non-experimental host plots.
Border Versus Interior Experiment
I carried out this experiment on Rosie's Organic Farm, a certified organic farm
located in southwest Gainesville, Florida. I chose this farm because it is a well-
established certified organic farm that had experienced outbreaks ofM. ochroloma and
the farmer was willing to participate in the research. The farm consists of two non-
contiguous fields; one of eight acres (3.2 ha) and the other of seven acres (2.8 ha). This
experiment involved only the eight-acre (3.2-ha) field. The soils are Entisols; mineral,
sandy soils with no obvious soil profile.
The field has been certified organic and managed organically since 1993. A
typical season begins at the end of the summer, when the cover crop (a combination of
cowpea and millet) is mowed and disked. Well-rotted chicken manure, the only fertility
amendment, is applied to the fields at the rate of 2 tons/acre (1814 kg/ha). Vegetables
and flowers are then seeded directly or transplanted from one of two greenhouses on the
I seeded mizuna, Brassica rapa, var. Kyona (untreated seed, from Johnny's
Seeds, Albion, ME) into four 72-cell transplant trays on 3 August 2001 and maintained
the plants in a greenhouse until transplant. I used Scotts Metro-Mix, specially blended
without starter fertilizer or wetting agents as the transplant media. No fertilizer was added
to the transplants initially, which halted the seedlings' growth, and delayed transplanting
by several weeks. I thinned the cells three weeks after planting, leaving only the largest
transplant in each cell. A single application of composted chicken manure was added one
month after seeding (during the first week of September).
I had initially planned to use the entire field for this experiment, and surveyed it
accordingly the last week of September. Because of the long growing season and
diversified nature of the farm, beds are prepared, planted, and harvested on an as-needed
basis. During the growing season at the farm, a single bed may be rotated through three
different crops. The result is that the eight-acre area is heterogeneous; some areas are
still in their summer cover crop while others are mowed and disked and ready to be
planted and some have already been planted. After considering these factors, I decided
to adjust the experimental design. The heterogeneity of the research site led me to divide
the field and choose a single homogenous area for this experiment. The mizuna host
plants were transplanted to into the experimental area on 2 October 2001.
I chose an experimental area in the northeast part of the field. The area consisted
of 18 rows on 6 ft. (1.83 m.) centers, running north-south, approximately 250 ft. (76.2 m.)
long. The rows had been planted in green beans and cucumbers during the first week of
September 2001. The north border was the edge of the field, bordered by successional
vegetation typical of this area of north Florida, including trees and shrubs and forbs. The
south border was the irrigation lines and walkway dividing the north and south sections
of the field. The east border was disked but unplanted. The west border was two rows of
turnips that had been planted around the middle of July 2001. In August 2001, I surveyed
the turnip rows and found several adult M. ochroloma, but no eggs or larvae and no
evident plant damage.
Beginning with the second (easternmost) row of turnips, I measured out
experimental plots of 3 ft. (0.914 m) long at either end (woods and interior) of every third
row. In each experimental plot, I planted 12 host plants in a three by four block. I
assigned interior plots the letters A through F and border plots the letters G through L
(Figure 3-1). I recorded the number of beetles (adults, larvae and eggs) on each host
plant in each plot at least twice a week beginning on 9 October 2001 and ending on 31
October 2001. By the end of October, many of the host plants had been completely eaten
by yellowmargined leaf beetles and I was no longer able to sample.
--------Mixed Crucifer Row-----
G --------------------------------- A
H ------------------------ B
I ---------------------------- C
K --------------------------------- E
L -----------Turnip----------F F
Figure 3-1. Field layout for border versus interior experiment. The dashed lines represent
rows that were not part of the experiment, and the letters designate the
experimental plots of host plants at both ends of the rows.
On two occasions (25 October and 29 October), I marked adult beetles using a
water-based paint and small paintbrush. I assigned each of the interior plots a color and
marked all the adults accordingly. The first time, I marked the beetles as I counted them.
The second time I collected the beetles in a container and then marked and counted them.
I then held the marked beetles in the container for 10 minutes, by which time the paint
appear dry. I then released the beetles back into the middle of their respective plots. On
the two subsequent sampling dates (27 October and 31 October) I recorded the number
and mark of all the beetles found in the experimental plots.
I used non-parametric methods to analyze the data. Graphing the untransformed
data, I found that the mean and variance were highly correlated. Neither square root nor
log transformations succeeded in diminishing this relationship to the point where the
parametric measures would have been appropriate. I used the Wilcoxon rank sum test
(Hollander and Wolfe 1999) to determine if there were differences between the numbers
of beetles on the field borders versus in the field interior. I used Kruskal-Wallis multiple
comparison test (Hollander and Wolfe 1999) to determine if there were differences
among the plots which were nearby, far away or a medium distance from the non-
experimental host plots. I used Wilcoxon comparisons post-hoc to test for differences
between the three pairs of treatments (near-far, near-mid, and far-mid) (Hollander and
I had three problems during this experiment. When I transplanted the host plants,
I noticed that there was evidence of beetle activity in one of the transplant trays. There
were several adults, a clutch of eggs and one newly hatched larva distributed among three
of the plants in this tray. I removed and killed the beetles, since I did not want to
introduce beetles to the field. Because the host plants were transplanted at a small size
and the beetles are very evident, I don't believe there were any more beetles on
previously transplanted trays and that this was an isolated incident.
A second problem was that each plot did not have a uniform host plant biomass,
nor did I correct my calculations to take this into account. The differences were not
systematic, i.e. all the plants on the interior were smaller than the ones on the border, but
Finally, my attempts to mark the yellowmargined leaf beetles failed. I did not
recapture a single marked beetle in subsequent sampling. I believe that the paint either
rubbed or washed off, or that I did not mark enough beetles relative to the total number of
beetles in the field to recapture them.
I carried out this experiment on Rosie's Organic Farm, a certified organic farm
located in southwest Gainesville, Florida. I seeded three 72-cell transplant tray of
mizuna, Brassica rapa, var. Kyona (untreated seed, from Johnny's Seeds, Albion ME)
and six trays of oak leaf lettuce, Lactuca sativa var. Berenice (untreated seed, Johnny's
Seeds, Albion, ME.) during the second week of January 2002. I maintained the plants in
a greenhouse until transplant. I used Scotts Metro-Mix, specially blended without starter
fertilizer or wetting agents as the transplant media. Transplants were thinned at three
weeks and fertilized every week after germination with fish emulsion fertilizer. On 15
March, I transplanted the seedlings to the field. The experimental design was a complete
randomized block, consisting of four treatments replicated four times. Each block
consisted of 32 plants.. The treatments were three densities of non-host plant (oak leaf
lettuce) to host plants 15:1, 7:1, and 3:1 plus a control plot that contained only mizuna.
The resulting blocks had 30 non-host plants plus two host plants, 28 non-host plants plus
four host plants, 24 non-host plants plus eight host plants and 32 host plants. The sixteen
blocks were randomized between two adjacent rows. I left a border space of 6 ft. (1.82
m) between each treatment plot. The location of the host plants within the treatment
block was selected using a random number table. There were no other host plants within
33 ft. (10 meters) of the experimental plots. Twice a week, from 16 March to 16 April, I
recorded the number of beetles per host plant and the position of the host plant.
I encountered several problems during this experiment. No adult yellowmargined
leaf beetles were present until the first week of April. I did not find any larvae or eggs
during the entire course of the experiment. I stopped sampling after 16 April because the
host plants were so badly damaged by other insects that I could not continue the
experiment. The other factor was that the nutsedge and pigweed that had been controlled
through hand weeding early in the season became completely out of control and took
over several of the experimental plots.
Again I used non-parametric methods for data analysis because of the correlation
between mean and varianace. I used the Jockheere-Terpstra test for ordered alternatives
(Hollander and Wolfe 1999) to determine if there were differences among the treatments.
I used the multiple-comparison Hayter-Stone test (based on Wilcoxon ranks) post hoc to
determine which plots were different.
Border Versus Interior Experiment
There were significantly more adult yellowmargined leaf beetles in the interior
plots than in those plots bordering the field edges (W= 52, P = 0.04). The border plots
(G-L) had a mean + SE of 8.17 + 3.67 adult beetles while the interior plots (A-F) had
54.5 + 20.42 beetles (Figure 4-1). There were no differences between border versus
interior location for either larvae or eggs (P = 0.45 and P = 0.42, respectively), although
the oviposition locations reflected a pattern similar to that of the adult population (Fig. 4-
2). The distribution of the yellowmargined leaf beetle larvae did not reflect the bimodal
distribution of the adults and eggs.
Adults Larvae Eggs
Figure 4-1 Mean number of yellowmargined leaf beetles in border versus interior plots
according to life stage, Gainesville, FL 2001.
The data were highly variable for the beetles' location in the border versus the
interior plots (Figure 4-2). Within the six experimental plots that comprised each of the
variables "border" and "interior", the adults, larvae and eggs were highly aggregated into
one or two plots. For example, I counted a total of 142 adult beetles in interior plot A,
but no beetles in plot B. Similarly, there were two eggs in interior plot B, but 467 in
interior plot A. I found the most larvae in the border plot 'I', which had 101 larvae but
no larvae in border plot L.
The relationship between number of adults and number of offspring was
inconsistent throughout the experimental plots. Plots with high larval populations and
high egg counts did were not always the plots with high adult populations in previous
weeks (Figure 4-3). Plot A had the most adult beetles, as well as the most beetle eggs but
only the fourth highest larval count. For example, plots D, 'I', and J, had relatively few
numbers of adult yellowmargined leaf beetles, but the second, third and fourth highest
egg counts later that week. Plots C, D, and E all had moderate and comparable numbers
of adults on 24 October, but subsequent oviposition varied as did their larval populations
A B C D E F G H I J K L
A B CD E F GH I J KL
S "- !
A B CD E F G H I J K L
Figure 4-2 Total number of yellowmargined leaf beetles collected from host plants,
Gainesville, FL 2001. Plots A-F are the interior plots; G-L are border plots.
Note the different y-axis scales.
* 3 1-Oct
If I n -* .
E 24 Oct AD
E 27 Oct EG
O 31 Oct LA
A B C D E F G H I J K L
Figure 4-3 Yellowmargined leaf beetle adult (AD), egg (EG) and larval (LA)
distributions during a one-week sampling period, Gainesville, FL 2001.
When I categorized the plots as nearby, medium distance or far away from other
crucifer plantings, there was no difference in the number of adult (X2 = 1.91, P = 0.43) or
larval (X2 = 0.94, P =0.66) yellowmargined leaf beetles in the experimental plots. Three
out of four of the plots categorized as near (plots F, G, and L) ranked towards the bottom
of all the plots for number of adult beetles and eggs. Plot A had the highest number of
adults overall, with 142. Plots A, F, and L ranked towards the bottom for number of
larvae, but Plot G had the second highest number of larvae, with 82.
The quantity of eggs in a plot did correspond to its proximity to other crucifer
plantings (X2 = 4.41, P = 0.11). Multiple comparisons using Wilcoxon ranks revealed
that the plots farthest away had more eggs than mid-distance plots (W= 3.266, P =
0.0739) but that there was no difference between the number of eggs in the nearest plot
and the farthest, or between the nearest and the mid-distance plot. The plots farthest from
other crucifer plantings had a mean + SE of 274.75 + 41.15 eggs, while the medium
distance plots had 60.25 + 33.51 eggs and the nearest plots had 135.75 + 110.82 (Figure
Near Mid Far
Figure 4-4 Mean number of yellowmargined leaf beetle eggs collected from experimental
plots based on the proximity of the plots to non-experimental host plants,
Gainesville, FL 2001.
I used the Jonckheere-Terpstra test for ordered alternatives to establish that there
was an increasing treatment effect (i.e. plots with fewer plants had fewer beetles) (J = 79,
P< 0.0056). (Figure 4-5) Multiple comparisons based on Wilcoxon ranks did not
establish which plots were different1. When plant density was taken into account, there
were no treatment differences among the intercrop plots (J= 48.5, P = 0.481). There
1 The critical value for the Hayter-Stone test at a= 0.10 is W= 2.873. The highest statistic
for these comparisons was for the monocrop to 1:15 treatment, which was W= 1.4.
were no more adult yellowmargined leaf beetles per plant in the monocropped (control)
plots than in any of the intercropped (treatment) plots nor were there differences among
yellowmargined leaf beetle populations per plant resulting from the various densities of
intercropped plants in the treatment plots. I did not find any larvae or eggs in the control
or treatment plots during the course of this experiment. However, there was a trend
towards higher number of adult yellowmargined leaf beetles as the experiment
progressed, indicating a seasonality effect (Figure 4-6).
S30 E 10-Apr-02
20 EO 16-Apr-02
1 0.25 0.125 0.0625
Host plant density
Figure 4-5 Mean number of yellowmargined leaf beetles collected on intercropped host
plants by date and host plant density2, Gainesville, FL 2002
2 Host plant density is the ratio of non-host plants to host plants. The least dense plots
of host plants (0.0625) had two host plants and 30 non-host plants (a ratio of 1:15 non-
host plants to host plants). The other treatment ratios are 1:7(0.125), 1:3 (0.25) and a
monocrop (control) plot containing all host plants, represented by 1.
Figure 4-6 Mean number of yellowmargined leaf beetles found on host plants,
Gainesville, FL 2002. Legend refers to the fraction of plants in a block that
are host plants.
Border Versus Interior Experiment
Whether or not M ochroloma experiences a true aestivation or not remains
unclear. While there does appear to be a pronounced summer dormancy, at least a
limited number of beetles are active during the summer months. During sampling in July
and August, I found a dozen adult yellowmargined leaf beetles on host plants. I did not
observe M. ochroloma feeding in the field. The yellowmargined leaf beetles that I
collected in the summer of 2001 mated and oviposited within 24 hours after I brought
them into the lab. This is not an expected response from beetles in a pre-diapause state;
but rather indicates that these beetles had not yet entered a preprogrammed diapause. I
also discovered a few eggs and first instar larvae on transplants as I was setting them in
the field on 2 October 2001. Finding beetles in the field during the summer and the
rapidity with which these field collected beetles mated and oviposited under laboratory
conditions suggests that M ochroloma has one of three distinct dormancy strategies.
The first possibility is that they are not diapausing but are quiescent. Danks
(1987) remarks that in insects whose lifecycle is directly controlled by temperature (i.e.
non-diapausing insects), emergence tends to be more staggered than post-diapause
emergence, due to variations among individual insects or differences in habitat
microclimate. The second possibility is thatM ochroloma is aestivating. Masaki (1980)
discusses five patterns of aestivation, one of which matches the apparent seasonal
patterns of the yellowmargined leaf beetle. Based on my field observations during 2001
and 2002, I believe that the yellowmargined leaf is dormant during the warmest part of
the year. The dormant period is both preceded and followed by periods of active feeding
and reproduction in the spring and then again in the fall, continuing on into the next
spring (Masaki 1980). It is not clear if an individual adult M ochroloma can oviposit
during both reproduction periods, or if mated beetles die off at the beginning of the
summer, with their newly hatched offspring entering diapause directly without mating,
and then emerging in the fall. If it is the latter, then what I collected in July and August
of 2001 are what is left of the early generation adults who have mated and will continue
to oviposit until death, without re-entering diapause. The rest of the population composed
of non-parous adults is in fact diapausing.
The third alternative is that the yellowmargined leaf beetle has multiple
oversummering strategies, as suggested by Masaki 1980) and similar those of the boll
weevil in the tropics and sub-tropics (Palmer and Cate 1992). In this scenario, most of
the population is in diapause, but a small percentage continue to feed and oviposit during
the normal aestival period.
Boiteau et al. (1979a) observed pre-dormancy flight to nearby woods for bean leaf
beetles, as did Voss and Ferro (1990) for Colorado potato beetles. Altieri (1994)
summarized multiple incidences of diapause migration in insects. However, it is not
evident that M ochroloma seeks oversummering habitat outside agricultural fields. I
found adult M ochroloma in interior plots first and the number of adults increased more
quickly in those plots. Most of these additional adults were recruited into interior plots
(rather than oviposited there), since the 23-day lifecycle ofM ochroloma is too long for
eggs to have hatched and be counted during the course of this study.
The higher populations of adult M. ochroloma in the field interior versus the field
border suggest that a large number of adults oversummer in the field. My sampling
indicates that large number of adults appear first in the autumn, followed in quick
succession by eggs. A period of several weeks elapses before larval populations build up.
Like other specialist herbivores, M. ochroloma likely oversummers near its feeding sites.
When the yellowmargined leaf beetle emerges, it begins feeding on the first acceptable
host plants it finds. No precise field records were available for the season previous to this
field study, to confirm that oversummering locations were in fact close to the last
season's feeding sites.
In addition to the higher adult populations in the field interior, there is a second
reason to conclude that the population of yellowmargined leaf beetles on this farm
oversummer within the field. While laying out the experimental plots on 26 September
2001, I surveyed the woody border along the northern border of the field. I looked
specifically for any cruciferous plants that might have served as alternate hosts for M
ochroloma during the summer months. I did not find any plants that were likely to serve
as suitable habitat for non-diapausing yellowmargined leaf beetles around the field edges.
Unlike the adult populations, egg and larval beetles ofM. ochroloma were equally
likely in border as well as interior sites. However, egg location showed a bimodal
pattern, similar to the pattern of adult location. Since eggs are sessile, their distribution is
the result of the adult female beetles' choice of oviposition sites. I believe that even
though the adults emerged in the field interior, they did not limit their oviposition to those
sites. This apparent dispersal by adult female beetles could be due to three different
factors. Female beetles may disperse their eggs as a "bet-hedging" strategy in case of
disaster or to avoid intraspecific competition as found with red milkweed beetles, T
tetraophthalmus (Matter 1997). A single female M. ochroloma can oviposit between
four to six eggs daily and is capable of a total fecundity of nearly 500 eggs (Ameen and
Story 1997b). With a single beetle capable of producing that quantity of offspring, my
data indicate that female beetles did not oviposit all their eggs in a single host plot.
Another other possibility is that adult beetles oversummered and emerged near
old feeding sites, but through nonrandom searching, some females found other host sites
more preferable and oviposited in those sites. Kareiva (1983) suggested that this type of
movement frequently takes place and can account for the observed damage among
treatments in an experimental field. It is also possible that the yellowmargined leaf beetle
has multiple oversummering strategies. Just as there may be multiple types of dormancy
in this population ofM ochroloma, there may be multiple dormancy locations as well.
While the majority of beetles oversummer in the field, some beetles may be
oversummering around field borders. The timing of dormancy induction and emergence
may vary somewhat within this population, with a group of beetles entering and emerging
together and the remainder emerging asynchronously both before and after the main
group. If the field oversummering beetles emerge and oviposit first, that could account
for their higher numbers in the interior plots initially. Beetles emerging later in the
autumn or from field borders (or both) may find the experimental border plots and
oviposit. If this second group happens to be smaller or oviposition takes place over a
longer period of time, a pattern of their emergence and oviposition may be harder to
detect than a larger group of beetles that emerges in a suitable field habitat
simultaneously and oviposits immediately. Tauber et al. (1988) described a similar
scenario for the Colorado potato beetle.
The larval distribution was dissimilar from both adult and egg locations. While
Nielsen (1988) indicates that adult chrysomelids do not move far during their lifespan,
my data indicate that the larvae are mobile within the scale of a single, small (<10 acre)
field. The lack of relationship between larval and adult locations is the evidence for
larval dispersal. The border and interior plots were located at opposite ends of 250 ft
(76.2 m) rows. On either given side of the field (border and interior) the experimental
plots were located 15 ft (4.57 m) apart. The beetles were allowed to move freely about
the field. In plot A, an interior plot with the most adults and highest number of eggs, I
did not record any larvae until 27 October, three weeks after the study began. This
indicates that once eggs hatched, the larvae likely moved to other feeding locations. The
closest experimental plot was B, which had no beetles or larvae, and only two eggs
during the duration of the study. However, the next closest plot of host plants was not B,
but a non-experimental plot of host vegetation. This non-experimental vegetation
consisted of a mixed row of kale and tat soi (Brassica oleracea, japonica group) on the
east end of the experimental plots (Figure 3-1); in other words located on the opposite
side of plot A than plot B. The beetles (adults or larvae) probably did not leave plot A,
skip over or walk around plot B and then choose a subsequent experimental plot (C or D)
to feed or oviposit. Instead, they moved to an area of non-experimental host plants.
Ameen and Story (1997) established that the food preferences ofM. ochroloma
vary with age, with adults preferring the largest variety of suitable hosts and first instars
preferring a single host. Narrower host preferences by earlier instars could also explain
the difference between adult and larval distribution.
Based on MacArthur and Wilson's (1967) theory of island biogeography
Janzen's (1968) subsequent interpretation and Root's (1973) resource concentration
hypothesis, I expected to find more yellowmargined leaf beetles in the plots closest to
alternative food sources (i.e. the biggest island, or in resource concentration terms, in the
most resource rich area). The larger islands are easier for colonizing beetles to locate, and
the abundance of food provides the incentive to remain in the area. The distribution of
M. ochroloma in this experiment did not conform to this theory. I believe that two
different processes occurred in the near plots. In plot A, which had the most adults, the
adults found the larger island, but their progeny did not remain there. While the adult
beetles emerging from dormancy or dispersing larvae may have found the larger islands
(created by plot A and its adjacent non-experimental host vegetation) more easily, the
concentration of resources did not keep the beetles within the experimental plots. The
adjacent non-experimental host plants may have been more attractive than the host plants,
in terms of architecture, or microclimate, host plant volatiles, or some other aspect of the
field layout, or perhaps provided a refuge from intraspecific competition. The result was
reduced larval populations in plot A. In effect, these non-experimental areas may have
acted more as trap crops rather than serving to increase the attractiveness of the area
overall. A similar result was obtained by Altieri and Schmidt (1986), who discovered
that host collards which received the least flea beetle (Phyllotreta cruciferae) damage
were located adjacent to wild mustard borders.
The other three near plots (F, G, and L) reflect two different situations. The high
number of larvae in plot G (a border plot) did not come from high numbers of eggs in that
plot, so the larvae clearly had moved to plot G from some other part of the field. In this
case, the concentration of food resources attracted larvae from outside that plot. Finally,
neither of the plots at the west end of the experimental area (plots F and L) attracted large
numbers of beetles in any stage. The effect of concentrated resources here did not attract
more beetles. I did not count the beetles in the alternative host plants to see if these
alternative (non-experimental) hosts had served as a trap crop instead of creating a bigger
island. While Ameen and Story (1997a) established that M ochroloma could distinguish
among several host plants and exhibits feeding preferences among these suitable hosts,
the relative preferences ofM ochroloma for the food plants in this particular experiment
have not been established.
In comparison, the experimental plots farthest away from the alternative host
plants retained their populations ofM. ochroloma. In effect, these far away plots served
as isolated, distant islands, on which yellowmargined leaf beetles became stranded and
concentrated in these plots. Altieri and Schmidt (1986) also found that P. cruciferae
populations were positively correlated with distance from the preferred mustard host
There was no difference between the nearest and middle distance plots, indicating that the
balance between dispersal and plot finding was equally likely from both types of plots.
The distribution of food resources is clearly not the only factor which influences
beetle distribution. The high degree of variability within both treatments (border and
interior) indicates that there is another underlying pattern to the distribution of the
yellowmargined leaf beetles that was not captured by this experimental design. I believe
that the location of emergence ofM. ochroloma and its initial feeding is likely to depend
on the location of last year's feeding sites. Beetles emerge close to old feeding sites, or
return to those sites first in search of suitable host plants. The differences between border
and interior populations could reflect the fact that interior plots were closer to old feeding
sites than border sites. The variation within the interior sites may reflect that those
locations with high beetle populations are in the same place as last year's crucifer
plantings, while those interior plots with low beetle populations are located farther away.
Without an accurate map of previous plantings, I had no way of knowing were crucifers
were planted the season before and the experimental plots were laid out without regard to
The distribution of M ochroloma within experimental plots was very uneven as
well. Yellowmargined leaf beetles were not spread among the 12 host plants per plot, but
clustered in just a few of the host plants. In a single plot, plants with only minor feeding
damage grew along side plants that were completely defoliated. While this pattern was
not captured in the data collection, it was evident when I examined the experimental
plots. Host plant searching techniques may be just as important as the location of
previous feeding sites in field distributions ofM. ochroloma. Host plant searching by
herbivores can be uniform or patch restricted (Stanton 1983). Insects that alter their
searching strategy upon finding a suitable host plant are engaging in patch restricted
searching. The result of patch restricted searching behavior is that insects remain in a
patch longer and are less likely to leave the patch, i.e. they have a longer "residence time"
in the patch.
Non-random insect distribution results indirectly from a heterogeneous
environment and patch restricted searching. Additionally, Morris et al. (1996) remark
that chrysomelid aggregations are formed directly over longer distances through
aggregation or mating pheromones or short range by visual and tactile cues from
conspecifics. Lewis (1994) used the term "herbivory-taxis" to describe the movement of
herbivores towards less damaged plants. Building on the idea of herbivory-taxis, Morris
et al. (1996) theorized that chrysomelid aggregations appear to move throughout an
environment when the insects engage in both herbivory-taxis and congregation based on
conspecific cues. Insects converge on a site, reduce the quantity and quality of the host
plant, and then collectively move on to a better site. The mass movement of M.
ochroloma from one host plant plot to another, and the aggregations of yellowmargined
leaf beetles within a single plot exemplify how congregation and herbivory-taxis could
act together under field conditions.
As mentioned previously, I did not correct for differing quantities of vegetation in
the experimental plots, nor did I assess any chemical or qualitative differences among the
host vegetation in the plots. Either or both of these factors may correlate with beetle
distribution in the experimental plots.
In his study of the arthropod community of cabbage, Pimentel (1961) found more
herbivores in dense plantings than sparse ones, but fewer herbivores per plant in dense
plantings. Specialist chrysomelids were fewer in polyculture plots, but those polyphagous
chrysomelids that consumed both squash and beans were more abundant in the squash/
bean polycultures (Risch 1981). Bach (1980) found more striped cucumber beetles in
monocropped systems. Like Pimentel (1961), Bach (1980) and Risch (1981), I found
more herbivores (in my case yellowmargined leaf beetles) in dense host plantings than
sparse ones. I did not find any differences, however, in the number of beetles per plant,
whereas Pimentel (1961) found fewer herbivores overall and Bach (1980) found more
striped cucumber beetles in monocropped systems, as did Risch (1981). Stanton (1983)
suggests that above a certain density of host plants, the environment becomes saturated
with food, resulting in lower herbivore loads. The seasonality effect that I observed
could have resulted from larger plants being easier for an herbivore to locate as the
season progressed, as suggested by Pimentel (1961).
Intercropping host plants among non-host plants was not effective in preventing
beetles from colonizing host plants. Microtheca ochroloma was able to find host plants
equally well in sparse planting as in dense plantings of host plants. The presence of the
non-host plants was not enough to diffuse the odor of the host plants, as Thiery and
Visser (1986) found with when they used cabbage and tomato plants to mask the odor of
potato host plants. In their study, Colorado potato beetles were disoriented by the
presence of the non-host plants (although they were not repelled by them) and were
unable to locate the potato plants Thiery and Visser (1986).
Coll and Botrell (1994) attributed the lower Mexican bean beetle densities in tall
corn-bean intercropping systems to a multitude of factors, including decreased
colonization by adults due to the tall corn impeding the flight of the beetles, and changes
in the light regime in the intercropped plots, which prevented E. varivestis from finding
its host. Neither of these factors affected the ability ofM. ochroloma to find its host
plants. Since the host and non-host plants were not of different heights and are of similar
architecture, the presence of the non-host plants did not discourage or confuse the
yellowmargined leaf beetle.
There were more total yellowmargined leaf beetles in the monoculture plots than
in the intercropped plots as predicted by Root's (1973) resource concentration hypothesis.
While they did aggregate around their host plants, this aggregation behavior was not
sufficient to produce a higher herbivore load (i.e. more beetles per plant). In contrast to
the patch-restricted searching that took place in the border versus interior experiment, the
beetles seem to engage in uniform searching when their population is low. Stanton
(1983) comments that populations of insects that engage in a uniform searching strategy
will be negatively correlated (or not correlated at all) with host plant density. This is
because plants in a higher density habitat have a proportionately less chance of being
selected than those plants which are sparsely planted.
The low population density in the intercropped plots failed to provoke the
"herbivory-taxis" behavior (and resulting feedback loop) seen under higher densities of
M. ochroloma. One or two adult yellowmargined leaf beetles may find a plant and feed
on it, without producing the herbivory damage of a large group of adults or larvae. A
congregation ofM ochroloma can quickly degrade its patch of food plants and the group
will be forced to move on. A beetle searching and feeding singly will be able to feed off
the same plant for much longer without degrading it, and thus has no incentive to keep
searching for host plants.
The pure stands of host plants represented islands that were larger or more
suitable for colonization than the individual plants interspersed among the non-host
plants, as the theory of island biogeography suggests (MacArthur and Wilson 1967).
However the intercropping treatments probably did not act as smaller and smaller islands
because in each of the three intercrop treatments, the host plants were distributed singly
throughout the intercrop treatment, not clumped together to represent islands of various
sizes. Similarly, Stanton (1983) suggests that herbivores do not recognize host plant
patches as such, but instead are sensitive to the size of the "peripheral distance around the
patch". The non-host plants did not confer associationall resistance" (as described by
Tahvanainen and Root 1972) to the host plants.
The role of competition and predation on M ochroloma are still unclear. Both
resource concentration hypothesis and natural enemies hypothesis work together in
regulating phytophagous insect populations (Root 1973). Natural enemies of M.
ochroloma have not been identified up to this point, either in M. ochroloma's introduced
or native range. I did not observe any predatory interactions during these experiments
nor did field collected yellowmargined leaf beetles exhibit signs of parasitism (Bowers,
unpublished). I do not believe natural enemies had any effect on these experiments.
Interspecific competition may have influenced the results of this intercropping
experiment. During this experiment the most significant damage to the mizuna host
plants was not due to M ochroloma, but to various Lepidopteran larvae. Root (1973)
suggested that interspecific competition decreased herbivore diversity in pure stands in
collards. The presence of other crucifer specialists may have deterred M ochroloma
from colonizing the experimental plots. I did not survey overall herbivore populations in
non-experimental areas of the field to compare with experimental areas, in order to see if
M. ochroloma populations were lower overall, or only in this experimental plot due to
I was not able to assess the how intercropping may have influenced M. ochroloma
mechanistically. While my results do not indicate differences in yellowmargined leaf
beetle population per plant due to the treatments, there may be differences in frequency
of host plant finding versus the duration of an insect's stay in a particular patch. As
suggested by multiple authors, including Garcia and Altieri (1992), Finch and Kostal
(1985), Finch and Collier (2000), Matter (1997) and Karevia (1983), insect populations
within a stand of plants may have as much to do with how long each insect remains in a
particular plot (i.e. how pleasing the plot is, or how many of the insects needs are met),
not just how easy the plot is to locate. Garcia and Altieri (1992) suggest that a
monoculture has chemical and physical qualities which "strongly attract, increase
permanence, or even re-attract" departing herbivores. Microtheca ochroloma may have
found the monoculture plots more easily than the intercrop plots, but the plots were not
suitable for some other reasons, perhaps interspecific competition. In my first experiment
(border versus interior experiment), I attempted to mark the beetles in order to establish
how much movement between plots determined plot population. In the same experiment,
the egg count gave some indication of how many adult beetles had visited a plot and
remained long enough to oviposit. I did not count any eggs in the intercropping
experiment, so it is difficult to know if there were any differences between plot finding
and oviposition among the treatments.
It is interesting that the overall population of yellowmargined leaf beetles in the
spring was much lower than in the fall. I did not find a single larva or egg in the spring
plots, while counts of eggs during the fall reached over 30 eggs per plant in the most
heavily infested plots. I contacted some of the same farmers I spoke with during the first
two seasons of my experiment and found that they had noted a marked decrease in
populations ofM ochroloma during the autumn of 2002. Reports of lower field
populations of yellowmargined leaf beetles in the fall 2002 season are anecdotal and have
not been quantified.
The long term goal of this research is to provide farmers with the basis for
ecologically-based cultural control methods for M ochroloma. Such methods are based
on a fundamental knowledge of an insect's life cycle and behavior that is still lacking in
this case. However, the results of this research have implications for current organic
farming practices. Accurate field records of previous crucifer plantings and beetle
outbreaks would be extremely useful in establishing a hypothesis on the source of beetle
outbreaks. If a farmer (or farmers) could record the timing and a precise field location of
host plants preferred by M ochroloma, subsequent beetle infestations could be correlated
with the location of the closest (or largest and closest) host plant patch. This type of
record-keeping could yield valuable information about how M ochroloma orients itself in
the field and locates its host plants.
Although the results of the intercropping study presented here are not
encouraging, I believe a longer term (multi-season) intercropping study might yield more
useful results. Alternate intercropping patterns may prove more successful than the one
tested in this study.
Directions for Future Study
I believe that establishing the source and timing of return of the yellowmargined
leaf beetles to an agricultural field will first require the answers to some more
fundamental questions. The focus for future research should establish the nature of
dormancy and emergence through controlled studies ofM. ochroloma behavior under
varying photoperiod and temperature regimes. Dissecting field-captured yellowmargined
leaf beetles (in the spring, summer and fall) to determine the state of their reproductive
organs and fat body is also essential in determining which stage ofM. ochroloma is
receptive to cues related to reproduction and dormancy.
Trap cropping may prove a useful control strategy for farmers who can afford the
space and time. Since M ochroloma can choose among host plants, a farmer might select
a less valuable crop as a trap crop and establish it in the vicinity of a more valuable one,
in order to draw M ochroloma away.
In terms of behavioral studies, I think that research using mark-recapture methods
and direction traps would be useful in a study of pre- and post- diapause movement of the
yellowmargined leaf beetle. This type of study would be essential in establishing their
While many authors (Ehrlich and Raven 1964, Dicke and Vett 1999, Matsuda
1988) have stressed the importance of chemical interactions between plants and
herbivores, a strict chemical co-evolutionary relationship is not universally accepted
(Bernays and Graham 1988). The study of chemical interactions between plants and
herbivores is still in its nascent stages; the chemical ecology ofM. ochroloma is
unexplored. The response of the yellowmargined leaf beetle to various host plant visual,
chemical and tactile stimuli will certainly provide evidence about how M ochroloma
locates suitable host plants. The scale over which host plant attraction occurs is
unknown, as is the nature of the attractants or stimulants (chemical or tactile or a
combination of the two). Various responses have been observed in other insects.
Hawkes and Coaker (1979) found that Delia radicum oriented to host plant volatiles in
the absence of tactile or visual cues. Finch and Collier (2000) propose that for D.
radicum to oviposit, it must first locate a plant and then receive repeated tactile stimuli.
How host plant allelochemicals and conspecific pheromones influence the behavior of M.
ochroloma is unknown. The behavioral and chemical studies involving Microtheca
ochroloma would be important in providing clues towards a general theory of host plant
finding by herbivores.
LIST OF REFERENCES
Altieri, M.A. (1994) Biodiversity and Pest Management in Agroecosystems Food
Products Press, New York.
Altieri, M.A., and Schmidt, L.L. (1986) Populations tends and feeding preferences of flea
beetles (Phyllotreta cruciferae Goeze) in collard-wild mustard mixtures. Crop
Protection, 5, 170-175.
Ameen, A.O. and Story, R.N. (1997a) Feeding preferences of larval and adult Microtheca
ochroloma (Coleoptera: Chrysomelidae) for crucifer foliage. Journal of
Agricultural Entomology, 14, 363-368.
Ameen, A.O. and Story, R.N. (1997b) Fecundity and longevity of the yellowmargined
leaf beetles (Coleoptera: Chrysomelidae) on crucifers. Journal of Agricultural
Entomology, 14, 157-162.
Andow, D.A. (1991) Vegetational diversity and arthropod population response. Annual
Review of Entomology, 36, 561-586.
Bach, C.E. (1980) Effects of plant density and diversity in the population dynamics of a
specialist herbivore, the striped cucumber beetle, Acalymma vittata. Ecology, 61,
Bernays, E. and Graham, M. (1988) On the evolution of host specificity in phytophagous
arthropods. Ecology, 69, 886-892.
Boiteau, G., Bradley, J.R., & Van Duyn, J.W. (1979a) Bean leaf beetle: Flight and
dispersal. Annals of the Entomological Association of America, 72, 298-302.
Boiteau, G., Bradley, J.R., & Van Duyn, J.W. (1979b) Bean leaf beetle: Some seasonal
anatomical changes and dormancy. Annals of the Entomological Association of
America, 72, 303-307.
Chamberlin, F.S. and Tippins, H.H. (1948) Microtheca ochroloma, an introduced pest of
crucifers, found in Alabama. Journal of Economic Entomology, 41, 979-980.
Coll, M. and Bottrell, D.G. (1994) Effects of nonhost plants on an insect herbivore in
diverse habitats. Ecology, 75, 7223-731.
Cromartie, W.J., Jr. (1975) The effects of stand size and vegetational background on the
colonization of cruciferous plants by herbivorous insects. Journal of Applied
Ecology, 12, 517-533.
Danks, H.V. (1987) Dormancy: An ecological perspective Biological Survey of Canada,
Dempster, J.P. (1969) Some effects of weed control on the numbers of the small cabbage
white (Pieris rapae L.) on brussels sprouts. Journal of Applied Ecology, 6, 339-
De Wilde, J., Duintjer, C.S. and Mook, L. (1959) Physiology of diapause in the adult
Colorado potato beetle (Leptinotarsa decemlineata Say). Journal of Insect
Physiology 3, 75-85.
Dicke, M. and Vet, L.E.M. (1999) Plant-carnivore interactions: Evolutionary and
ecological consequences for plant, herbivore and carnivore. In Herbivores:
Between Plants and Predators (eds H. Olff, K. Brown and R.H. Dent), pp. 642.
Blackwell Publishers, London.
Ferguson, C.S., Linit, M.J., and Krause, G. (1991) Host-plant preference of the Asiatic
oak weevil (Coleoptera: Curculionidae). Environmental Entomology, 20, 1427-
Finch, S. and Collier, R.H. (1985) Laboratory studies on aestivation in the cabbage root
fly Delia radicum. Entomologia Experimetalis et Applica, 38, 137-144.
Finch, S. and Collier, R.H. (2000) Host plant selection by insects--A theory based on
"appropriate/inappropriate landings" by pest insects of cruciferous plants.
Entomologia Experimetalis et Applica, 96, 91-102.
Ehrlich, P.R. and Raven, P.H. (1964) Butterflies and plants: a study in coevolution.
Evolution, 18, 586-608.
Frank, J.H., McCoy, E.D., Hall, H.G., O'Meara, G.F., and Tschinkel, W.R. (1997).
Immigration and introduction of insects. In Strangers in Paradise: Impact and
Management of Nonindigenous Species in Florida (eds D. Simberloff, D.C.
Schmitz & T.C. Brown), pp. 467. Island Press, Washington D.C.
Follett, P.A. and Roderick, G.K. (1996). Adaptation to insecticides in Colorado potato
beetle: single- and meta-population models. In Chrysomelidae Biology (eds P.
Jolivet & M.L. Cox), Vol. 2, pp. 465. SPB Academic Publishing, Amsterdam.
Garcia, M.A. and Altieri, M.A. (1992) Explaining the differences in flea beetle
Phyllotreta cruciferae Goeze densities in simple and mixed broccoli cropping
systems as a function of individual behavior. Entomologia Experimetalis et
Applica, 62, 210-209.
Georghiou, G.P. (1986). The magnitude of the resistance problem. In Pesticide
Resistance: Strategies and Tactics for Management (ed N.R. Council), pp. 471.
National Academy Press, Washington, D.C.
Haeussler, G.J. 1951. Special insects of regional significance: Yellowmargined leaf
beetle (Microtheca ochroloma). United States Department of Agriculture
Cooperative Economic Insect Report 1: 124.
Hawkes, C. and Coaker, T.H. (1979) Factors affecting the behavioral responses of the
adult cabbage root fly, Delia brassicae, to host plant odours. Entomologia
Experimetalis Et Applica, 25, 45-58.
Hicks, K.L. (1974) Mustard oil glucosides: Feeding stimulants for adult cabbage flea
beetles Phyllotreta cruciferae (Coleoptera: Chrysomelidae). Annals of the
Entomological Society of America 67, 261-264.
Hollander, M. and Wolfe, D.A. (1999) Nonparametric statistical methods. John Wiley &
Sons, New York.
Janzen, D. (1968) Host plants as islands in evolutionary and contemporary time.
American Naturalist, 102, 592-595.
Jolivet, P. and Hawkeswood, T.J. (1995) Host-plants of Chrysomelidae of the world
Backhuys Publishers, Leiden, Germany
Kareiva, P. (1983). Influence of vegetation texture on herbivore populations: resource
concentration and herbivore movement. In Variable Plants and Herbivores in
Natural and Managed Systems (eds R.F. Denno & M.S. McClure). Academic
Press, New York.
Kostal, V. and Finch, S. (1994) Influence of background on host-plant selection and
subsequent oviposition by the cabbage root fly (Delia radicum). Entomologia
Experimetalis Et Applica, 70, 153-163.
Latheef, M.A., Ortiz, J.H., and Skeikh, A.Q. (1984) Influence of intercropping on
Phyllotreta cruciferae (Coleoptera: Chrysomelidae) populations on collard plants.
Journal of Economic Entomology, 77, 1180-1184.
Lewis, M.A. (1994) Spatial coupling of plant and herbivore dynamics: The contribution
of herbivore dispersal to transient and persistent "waves" of damage. Theoretical
Population Biology, 45, 277-312.
Lipson, M. (1997). Searching for the O-word: An analysis of the USDA Current
Research Information System (CRIS) for pertinence to organic farming. Organic
Farming Research Foundation, Santa Cruz, CA.
Masaki, S. (1980) Summer diapause. Annual Review of Entomology, 25, 1-25.
MacArthur, R.H. and Wilson, E.O. (1967) The Theory of Island Biogeography Princeton
University Press, Princeton, N.J.
Matsuda, H. (1988). Feeding stimulants of leaf beetles. In Biology of Chrysomelidae (eds
P. Jolivet, E. Petitpierre & T.H. Hsiao), pp. 614. Kluwer Academic Publishers,
Matter, S.F. (1997) Population density and area: The role of between- and within-patch
processes. Oecologia, 110, 533-538.
Morris, W., Grevstad, F., and Herzig, A. (1996). Mechanisms and ecological functions of
spatial aggregation in chrysomelid beetles. In Chrysomelidae Biology (eds P.
Jolivet & M.L. Cox), Vol. 2, pp. 303-322. SPB Academic Publishing,
National Agriculture Statistics Service. Florida Agricultural Facts 2001. Available from
URL: http://www.nass.usda.gov/fl/rtocO.htm. Last accessed 28 March 2003
Nielsen, J.K. (1988). Crucifer-feeding Chrysomelidae: Mechanisms of host plant finding
and acceptance. In Biology of Chrysomelidae (eds P. Jolivet, E. Petitpierre and
T.H. Hsiao), pp. 614. Kluwer Academic Publishers, Dordrecht.
Oliver, A.D. 1956. Special insects of regional significance: Yellowmargined leaf beetle,
(Microtheca ochroloma). United States Department of Agriculture Cooperative
Economic Insect Report 6:352.
Oliver, A.D. and Chapin, J.B. (1983) Biology and distribution of the yellowmargined leaf
beetle Microtheca ochroloma Stdl, with Notes on M. picea (Guerin) (Coleoptera:
Chrysomelidae) in Louisiana. Journal of the Georgia Entomological Society, 18,
Palmer, J.O. and Cate, J.R. (1992) Overwintering survival of prereproductive and
postreproductive boll weevils (Coleoptera:Curculionidae). Environmental
Entomology, 21, 117-120.
Pimentel, D. (1961) The influence of plant spatial patterns on insect populations. Annals
of the Entomological Association of America, 54, 61-69.
Ramnath, S., Chitra, K., and Uthamasamy, S. (1992) Behavioral responses of
Helicoverpa armigera (Hubner) to certain host plants. Journal of Insect Science,
Risch, S.J. (1981) Insect herbivore abundance in tropical monocultures and polycultures:
an experimental test of two hypotheses. Ecology, 62, 1325-1340.
Root, R.B. (1973) Organization of a plant-arthropod association in simple and diverse
habitats: The fauna of collards (Brassica oleracea). Ecological Monographs, 43,
Simberloff, D. (1997). The biology of invasions. In Strangers in Paradise: Impact and
Management of Nonindigenous Species in Florida (eds D. Simberloff, D.C.
Schmitz and T.C. Brown), pp. 467. Island Press, Washington D.C.
Smith, H.A. and McSorley, R. (2000) Intercropping and pest management: A review of
major concepts. American Entomologist, 46, 154-161.
Sooby, J. (2001). State of the States: Organic farming systems research at land grant
institutions 2000-2001. Organic Farming Research Foundation, Santa Cruz, CA.
Spink, W.T. 1959. Truck crop insects: Yellowmargined leaf beetle (Microtheca
ochroloma). United States Department of Agriculture Cooperative Economic
Insect Report 9: 355.
Staines, C.L. (1999) Chrysomelidae (Coleoptera) new to North Carolina. The
Coleopterists Bulletin, 53, 27-29.
Stanton, M.L. (1983). Spatial patterns in the plant community and their effect upon insect
search. In Herbivorous Insects: Host-Seeking Behavior and Mechanisms (ed S.
Ahmad), pp. 320. Academic Press, New York.
Strauss, S. (1988). The Chrysomelidae: A useful group for evaluating herbivore-
herbivore interactions. In Biology of Chrysomelidae (eds P. Jolivet, E. Petitpierre
& T.H. Hsiao), pp. 614. Kluwer Academic Publishers, Dordrecht, Netherlands.
Tahvanainen, J.O. and Root, R.B. (1972) The influence of vegetational diversity on the
population ecology of a specialized herbivore Phyllotreta cruciferae (Coleoptera:
Chrysomelidae). Oecologia, 10, 321-346.
Tauber, M.J., Tauber, C., Obrycki, J., Gollands, B., and Wright, R.J. (1988) Voltinism
and the induction of aestival diapause in the Colorado potato beetle, Leptinotarsa
decemlineata (Coleoptera: Chrysomelidae). Annals of the Entomological
Association of America, 81, 748-754.
Thiery, D. and Visser, J.H. (1986) Masking of host plant odour in the olfactory
orientation of the Colorado potato beetle. Entomologia Experimetalis et Applica,
Voss, R.H. and Ferro, D.N. (1990) Ecology of migrating Colorado potato beetles
(Coleoptera: Chrysomelidae). Environmental Entomology, 19, 123-129.
Woodruff, R.E. (1974) A South American leaf beetle pest of crucifers in Florida. Florida
Department of Agriculture and Consumer Services, Division of Plant Industry,
Kristen Bowers was born in Washington, D.C., in 1974. She graduated with a
bachelors' degree in economics from the University of Virginia in 1996. She served in
the Peace Corps in Nicaragua from 1996 to 1998. She is currently employed by USDA-
ARS in Tallahassee, Florida.