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Polyphagy in True Bugs: A case study of
Leptoglossus phyllopus (L.)
(Hemiptera, Heteroptera, Coreidae)1
P.L. MITCHELL
Abstract: The polyphagous species Leptoglossus phyllopus(L.) was examined with respect to host plant
preference, tissue feeding specificity, seasonal dispersal among host plants, and life history. Mark-recap-
ture, census, and rearing experiments demonstrated that this species exhibits true polyphagy, in that in-
dividual bugs feed on plants from more than one family. Developmental parameters such as growth and
survivorship did not differ among plants from several families, but did vary significantly with quality of
host (e.g., wild vs. cultivated). Stadium duration, however, varied among wild host plant species in la-
boratory experiments. Specialization on reproductive plant parts, coupled with sequential polyphagy
and dispersal among a variety of seasonal host plants, allows multiple generations per year. Modes of fee-
ding and preferred target tissues among coreids are discussed.
Key words: leaffooted bug,Leptoglossus phyllopus, polyphagy, stylet sheath, target tissue.
Introduction spp.), for example, employ a macerate-and-
flush process, whereas an osmotic pump
For phytophagous insects with piercing-
mechanism is associated with coreids (MILES
sucking mouthparts, feeding selectivity op-
& TAYLOR 1994). However, some pentato-
erates on two levels: preferred target tissue
mids and lygaeids shift between salivary
and host plant species. Tissue preference is
sheath formation and lacerate-and-flush
considered to be a conservative evolution-
feeding (MILES1972).
ary character (TONKYN & WHITCOMB
1987); for example, specialization on xylem, Preference for a particular plant devel-
phloem, or parenchyma is characteristic of opmental stage or structure (e.g., growing
subfamilies or families in Auchenorrhyncha shoots, buds, ripe seeds), may also be associ-
(PORT 1978). Phytophagous Heteroptera ated with specific groups. Pyrrhocoroidea
have been extensively analyzed with respect feed predominantly on mature seeds, tingids
to several factors associated with target tis- prefer mature leaves, while phytophagous
sue preference: mouthpart morphology, sali- mirids concentrate on flowers, buds, and
vary chemistry, preference for plant parts or new foliage (SCHUH & SLATER 1995). In
structures, and mode of feeding (MILES some cases, however, such trends only be-
1972; COBBEN1978; MILES& TAYLOR1994; come evident at the tribal or even generic
HORI 2000). The enzyme components of level. SCHAEFER & MITCHELL (1983) noted
heteropteran saliva are considered to be a that an affinity for vegetative or reproduc-
family-level character (MILES, cited in HORI tive structures is characteristic of tribes
2000), although induction of proteolytic en- within the Coreidae. Among Australian
zymes has been demonstrated in a zoophy- coreids, KUMAR (1966) recognized two dif-
tophagous mirid (ZENG & COHEN 2001). ferent types of feeding – exclusive sap feed-
The mode of feeding may also be associated ing is found in some genera whereas others
with particular taxa. Mirids (e.g., Lygus feed on both sap and fruit. However, such
Denisia 19, zugleich Kataloge
1Dedicated affectionately to Ernst Heiss, my delightful colleague on the Executive Committee of the International der OÖ. Landesmuseen
Heteropterists’ Society and heteropterist extraordinaire. Neue Serie 50 (2006), 1117–1134
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diversity of feeding was considered by phytophagous groups, he proposed that sap-
COBBEN (1978) to indicate a “phase of un- feeding originated from polyphagous seed-
balanced equilibrium.“ feeding, with the former mode of feeding
tending toward a more restricted host range
Even fewer generalizations may be made
(COBBEN 1978). In Hemiptera in general,
regarding host-plant specificity. Curiously,
tissue-feeding specialization has been associ-
the question of diet breadth in Heteroptera
ated with host plant specificity (BERNAYS&
has not been explored with the intense fer-
CHAPMAN 1993), but this observation is
vor devoted to insect-plant interactions in
based primarily on the British fauna, and is
Lepidoptera, Orthoptera, and other orders
biased toward Sternorrhyncha and Auchen-
of chewing insects. COBBEN (1978) charac-
orrhyncha. Clearly, more information on
terized the Tingidae as monophagous while
polyphagy in Heteroptera is needed.
suggesting that “polyphagy prevails“ among
the phytophagous Miridae; but he provided The objective of this research was to
no comparable analysis for the Pentatomo- conduct a detailed study of polyphagous
morpha. Nearly 30 years have passed since feeding behavior in a single coreid species,
the publication of COBBEN’s (1978) monu- the leaffooted bug Leptoglossus phyllopus
mental study of mouthparts and feeding (L.). Host range and dispersal, seasonal pat-
strategies, but our understanding of het- terns of host plant use, preferred feeding
eropteran-plant relationships remains limit- site, and target tissue were examined in or-
ed. Neither facultative zoophagy nor the ex- der to characterize the factors influencing
treme polyphagy associated with some het- host plant selection. Leptoglossus phyllopus
eropterans is properly understood (ZENG & damages legumes, tomatoes, tree nuts, and
COHEN 2001). WHEELER (2001) observes citrus in the southern and eastern United
that despite an extensive literature on crop States (MITCHELL2000), and is considered a
injury, there are “large gaps in our knowl- minor economic pest. The primarily
edge of mirid-plant interactions.“ Informa- Neotropical genus Leptoglossus GUERIN was
tion for some heteropteran groups is lacking, selected for study because it includes species
detailed ecological studies of bugs outside of exhibiting widely disparate feeding strate-
agroecosystems are uncommon, and adult
gies ranging from strict monophagy to ex-
host plant records are not always reliable in-
treme polyphagy, as well as a number of
dicators of breeding hosts (SCHAEFER & species of economic importance. Several
MITCHELL1983). Leptoglossusspecies are presently expanding
Polyphagy in Heteroptera is of great in- their ranges – and potential for economic
terest from both an economic and an evolu- damage – geographically. The highly
tionary standpoint. Many of the major agri- polyphagous L. zonatus (DALLAS), a pest of
cultural pests (e.g., Nezara viridula(L.), Rip- many crops in Mexico and South America,
tortus clavatus (THUNBERG), Leptoglossus has recently invaded the southeastern Unit-
zonatus (DALLAS), Lygus lineolaris (PALISOT ed States to Florida (BUSS et al. 2005) and
DE BEAUVOIS)) have a wide range of host has become a pest of Satsuma oranges in
plants (SCHAEFER& PANIZZI2000). Howev- Louisiana, displacing L. phyllopus (HENNEet
er, it is important to distinguish between al. 2003). Leptoglossus occidentalis HEIDE-
generalist species composed of more special- MANN, once restricted to conifers in western
ized populations and polyphagy at the indi- North America, has spread rapidly eastward
vidual level (i.e., diet mixing) (FOX& MOR- across the continent to Ontario and New
ROW 1981; BERNAYS & MINKENBERG 1997). England (RIDGE-O’CONNOR 2001). Acci-
The evolution of omnivory has been shown dentally introduced into Italy in 1999 (TAY-
to correlate with polyphagy in Heteroptera LORet al. 2001), this species has now spread
(EUBANKS et al. 2003), and these authors to Central Europe (RABITSCH & HEISS
proposed that polyphagous, seed-feeding 2005). Thus, information on the feeding be-
herbivores may be more likely to expand the havior of L. phyllopusmay be applicable not
diet to consume animal prey. COBBEN(1978, only in the southeastern United States, but
1979) considered polyphagous carnivory to to congeneric species of economic impor-
be plesiomorphic within Heteroptera. For tance elsewhere.
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Materials and Methods Both L. phyllopus and another coreid, Eu-
thochtha galeator(F.), were monitored. Num-
Study site:Research was conducted pri-
ber of adults, nymphs of all instars, and cop-
marily at Brackenridge Field Laboratory
ulations were counted. Location of bugs on
(BFL), operated by The University of Texas
the plant was noted in greater detail than in
at Austin. This field station is located inside
earlier censuses, differentiating between
the city limits of Austin, Texas, along the
bud, stem, and leaf primordia as well as be-
shores of the Colorado River, and comprises
tween mature plant organs. The 1979 cen-
32 hectares of grassland, cedar-post oak
sus covered the entire reproductive life span
scrub and semi-deciduous woodland.
of the host plant Cirsium texanum BUCKL.,
Four study plots, each measuring 92.9 from bolting through seed set.
m2, were established at BFL to investigate
A plant census was conducted monthly
seasonal activity of L. phyllopus and other
in each study site in conjunction with the
coreids. All plots were located in either ear-
bug censuses in 1977 and 1978. Each plot
ly successional or cultivated garden areas.
was subdivided into 40 equal quadrats, and a
Plot 1, on the river terrace, was dominated
wire square measuring 930 cm2 was tossed
by Johnsongrass, Sorghum halepense (L.)
twice into each quadrat. This quadrat
PERS.,and various composite species. Plot 2, method was designed to eliminate the un-
bordering an artificial pond, was composed
equal representation of marginal areas fre-
primarily of grasses and composites inter-
quently associated with sampling by random
spersed with prickly pear (Opuntia spp.) and
toss (SOUTHWOOD1966). After each throw,
mesquite (Prosopis glandulosa TORR.). The presence or absence of plant species within
remaining study plots were placed in the the wire sampler was noted, in order to com-
cultivated garden area to ensure an adequate pute frequency of occurrence from a total of
water supply during summer drought. Plot 3, 80 samples per study plot. Additionally,
formerly under cultivation, had returned to counts were taken of number of stems, buds,
native early successional vegetation two flowers, developing fruits, and mature fruits
years before the commencement of research. of host plants within the confines of the
Plot 4, the agricultural study plot, was plant- wire square. All counts were made visually
ed each spring with tomato (Lycopersicon es- in the field, and no plant material was re-
culentum P. MILL.), giant sunflower (He- moved from the study areas. All Leptoglossus
lianthus annuus L.), and okra (Hibiscus host plants were identified to species. With
[=Abelmoschus] esculentus L.). A sprinkler the exception of grasses, non-hosts were
system provided water for both garden plots identified at least to genus. Within the
twice weekly, and fertilizer was applied to Poaceae only S. halepensewas distinguished;
cultivated plants according to standard other grasses were lumped in a single cate-
agronomic practices. gory. Plant family designations follow JUDD
et al. (2002); species and describer names
Field census: From July to November
1977, and February to November 1978, L. follow RADFORDet al. (1968) and CORRELL
phyllopusindividuals were visually counted in & JOHNSTON (1970). In 1979, only host
plants were surveyed. Finer distinctions
each study plot at weekly intervals. All cen-
were used in the census of plant structural
suses were taken within two hours of sunset,
and reproductive organs, to correspond with
a time of maximal copulation and feeding ac-
the more detailed bug distribution studies.
tivity. Field work was discontinued during
the winter (mid-November through mid- For statistical analysis, plants were cate-
February), as no bugs were active during this gorized as reproductive or non-reproductive,
period. For each individual observed, the fol- and bug counts (log bug density for each
10
lowing data were collected: location on plant non-zero census date) were correlated with
(leaf, stem, bud, etc.), plant species and re- density of reproductive plants for C. tex-
productive condition, instar (nymphs), and anum in Plot 1 and Heterotheca latifolia
copulatory activity (adults). BUCKL. in Plots 2 and 3.
From March to June 1979, a modified Mark-recapture: Mark-release-recap-
bug census was conducted weekly in Plot 1. ture studies were carried out at BFL from
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Fig. 1: Leptoglossus phyllopus adults; June 1976 through November 1977. Adult bugs to emerge. The effect of prominent
clockwise from upper left: aggregated on L. phyllopus were individually marked by white dorsal markings on bugs in the field is
Cirsiumsp., March, Brazos Co., Texas
painting the pronotum with typewriter cor- unknown, but this technique does not sig-
(Photo: W. O. Ree Jr.); in copula on Gaura
parviflora, July, Burleson Co., Texas (Photo: rection fluid (Liquid Paper™) and number- nificantly alter survivorship or copulatory
A. Calixto); aggregated with marked bug ing with india ink (Fig. 1). A total of 1,070 activity of individuals under laboratory con-
on Helianthus annuus, August, Travis Co.,
individuals was marked during the course of ditions (Mitchell unpubl. data). Mark-re-
Texas; feeding on Solidagosp., October,
Brazos Co., Texas (Photo: W. O. Ree Jr.); the study. Bugs were collected in the field by lease-recapture studies were designed to ex-
feeding on G. parviflora, July, dropping net bags over aggregations on host amine dispersal, host plant shifts, and length
Burleson Co., Texas (Photo: A. Calixto).
plants, and were returned to the laboratory of residency, rather than population size.
for marking. With rare exceptions, each Consequently, initial marking was a discon-
batch was completed and released on the tinuous process, although study areas were
date of capture. Bags of marked individuals checked daily or twice daily for recaptures.
were attached to a branch or stem of the Thirteen subsites (host plant patches) were
original host plant and opened, allowing delineated in the mark-release-recapture
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study. Size of subsites was variable, being a Colony maintenance: Leptoglossus phyl-
function of host plant density in a given lopus colonies were reared at 26 ±2°C, and
area, and ranged from a single Callicarpa a photoperiod of 16:8 [L:D], and were fed
americanaL. bush to a 30 m2stand of H. lat- whole green beans, Phaseolus vulgarisL. and
ifolia. Distance between subsites was meas- shelled organically grown sunflower (H. an-
ured from center to center of each patch. nuus) seed. Adults were housed in screen
Analysis of dispersal therefore did not ac- and Plexiglas™cages (25 x 25 x 25 cm) pro-
count for movement within the larger sub- vided with wooden applicator sticks for
sites, and total movement may have been oviposition. Nymphs were maintained in
slightly underestimated. Each subsite was smaller cages constructed from 300 ml plas-
characterized by one dominant host plant tic drinking cups (cup cages) and provided
species. with a constant source of water through cot-
ton dental wicks.
The following data were collected for
Rearing experiments: Conducted in
each marked individual: sex, subsite, time of
both laboratory and field, these experiments
collection, host plant species, absence of
examined the ability of fifth-instar L. phyllo-
legs, presence (and position) of macrotype
pusto develop on a variety of hosts from dif-
tachinid eggs on exoskeleton, degree of scle-
ferent plant families at different stages of de-
rotization (teneral vs. mature) and wing
velopment. Three variables were used to
wear condition (tattered vs. whole). Begin-
measure host plant suitability: duration of
ning in August 1976, bug length was meas-
the fifth instar, growth increment during
ured with calipers to the nearest 0.5 mm. At
this period, and survivorship. Experimental
each subsequent recapture original observa-
bugs were derived from field collected par-
tions were rechecked, with the exception of
ents, and were reared in the laboratory.
length measurement. Further information
Rearing colony cages were checked nightly,
collected for resighted individuals included
at growth chamber sunset. All newly molted
location on host plant and activity (e.g., sit-
fifth instars were collected at this time, iso-
ting, walking, probing, sucking, copulating).
lated in screen-covered cups overnight, and
Data from the pilot study (June to Sep- supplied with a green bean for moisture.
tember 1976) and overwintering periods Distribution of nymphs among treatments
(October to February of both years) were was completed within 24 hours. Assignment
analyzed separately from the major mark-re- to treatment was randomized within the set
lease-recapture project in 1977. Marking of of host plants in the appropriate develop-
the overwintering generation proved unsuc- mental condition at a given point in time.
cessful; no bugs marked in late fall of either
Each nymph was measured with calipers
year were ever sighted again the following
to the nearest 0.5 mm before placement on
spring. Pilot project data were analyzed by
the experimental host plant. Cages were
hand to determine host plant and subsite
checked daily at sunset, and newly molted
shifts by individual bugs.
adults were re-measured. Growth increment
The mark-release-recapture project in was calculated as the difference between
1977 involved a total of 543 individuals and these two length measurements. Instar dura-
three complete generations of L. phyllopus. tion was defined as days elapsed between the
fifth instar and adult molts. Survivorship,
Bugs were separated into four generational
assessed only in laboratory experiments, was
categories (overwintering, spring, summer,
calculated as number of surviving nymphs
fall) on the basis of wing wear and scleroti-
per cage.
zation. Data were processed using the
LONGPOP program (WATT et al. 1977, In the laboratory, detached fruits or seed
1979). This program applies the capture-re- heads of a single plant species were offered
capture methods of JOLLY(1965) for calcula- as a food source. Each experimental cup
tion of survivorship, and also tabulates dis- cage contained five bugs, individually
persal and other population parameters. Sex marked with enamel dots on the tibial folia-
ratios were tested using χ2 goodness-of-fit tion. Laboratory experiments involved six
(ZAR1999). treatments, consisting of laboratory diet
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control and five host plants: Callicarpa amer- Field data from mark-recapture studies
icana L. var. lactea (Lamiaceae), Campsis were also analyzed to substantiate the exper-
radicans (L.) SEEM. (Bignoniaceae), Gaura imental results for fifth instar growth incre-
parviflora DOUGL. (Onagraceae), and ment. Adult length of L. phyllopus marked
Solanum eleagnifolium CAV. (Solanaceae). as teneral individuals was compared among
Each treatment consisted of four cages for a various host plants. Adult length of males
total of 20 nymphs per treatment. and females was analyzed separately for
these data, because sex ratios were not
In field experiments, bugs were caged
equivalent across treatments.
individually on live host plants (n = 25).
Tulle sleeves, measuring 45 by 25 cm, were Measurement data from both field and
lowered around plant stems or branches, laboratory experiments were analyzed by t
and fastened at the base with fine wire. Veg- tests or by one way analyses of variance
etative portions of the plant, flower buds, or (ANOVA) followed by Fisher’s LSD. Loga-
one or more developing seed heads (de- rithmic (base-10) transformation was used
pending on the growth form of the plant) prior to ANOVA if needed to normalize da-
were contained within each sleeve cage. Af- ta or correct for unequal variance (MINITAB
ter addition of a nymph, each sleeve was 2000). Count data were analyzed by non-
wired together at the top, enclosing both parametric tests, including Friedman two-
bug and plant. Plants were maintained in way ANOVA, Kruskal-Wallis (MINITAB
the bud stage by clipping flowers within the 2000), and non-parametric rank analog of
cage as they opened, or moving the entire Tukey’s test (CONOVER1971).
cage to a new plant. Field experiments con-
Laboratory choice tests:Choice exper-
centrated mainly on species in the family
iments were conducted in small cup cages.
Asteraceae. Treatments included Baccharis
Naive second instars were used in all tests.
neglecta BRITT. (Astereae), C. texanum Field observations identified this instar as
(Cynareae), Gutierrezia texana (DC) TORR. the first critical period of host plant selec-
& GRAY (Astereae), H. annuus (He- tion, because the previous instar is a non-
liantheae), H. latifolia (Astereae), Solidago
feeding stage, and oviposition site does not
altissima L. (Astereae), and G. parviflora
necessarily reflect host plant preference
(Onagraceae). The last four species were
(MITCHELL & MITCHELL 1986). Nymphs
tested in all three developmental stages;
used in experiments were derived from field-
other hosts listed were tested only in repro-
collected adults, but reared from the egg
ductive condition.
stage in the laboratory. Prior to placement
Field experiments were conducted from in testing cages, bugs received only green
September to November of 1977, and May bean (a water source), and were not exposed
through July of 1978, according to the phe- to laboratory diet.
nology of host plants studied. Separating the Since early instar nymphs are normally
influence of climatic variation from genuine gregarious, bugs were tested in groups of five
treatment effects was therefore critical. A per cage. Preference between plant species
series of controls was established, in order to was tested by offering seed heads of H. lati-
monitor the combined effects of tempera- folia (Asteraceae) and G. parviflora (Ona-
ture and daylength and also laboratory stock graceae) as alternative food choices; prefer-
quality. In the laboratory control treatment, ence for plant parts was tested using buds
bugs received standard rearing diet (beans, and immature seed heads of C. texanum. For
sunflower seeds and distilled water), and each comparison, 36 replicates were con-
were maintained in the growth chamber at ducted, using a total of 180 second instars.
16:8 [L:D] photoperiod conditions. Addi- Each testing cage contained one cut stalk
tionally, tulle cages supplied with laboratory (ca. 8 cm) of each plant alternative, insert-
diet were set up on the roof of the Zoology ed in separate water vials. Fresh plant cut-
building on the University of Texas campus. tings for each experiment were collected
One set of these “roof controls“ was con- daily at the field station. Following addition
ducted in fall of 1977, and one in summer of of nymphs, cages were observed at 4-h inter-
1978. vals during the 16-h growth chamber day,
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and again at sunrise of the following day. Stylet tracks of L. phyllopuswere exam-
Stylet insertion was considered to represent ined on the wild host C. texanum, and also
definitive choice. A single observation, that on cultivated green cherry tomato (L. escu-
which involved the greatest number of feed- lentum), and green bean (P. vulgaris). In ad-
ing individuals, was selected from each ex- dition, feeding by the coreid E. galeator on
perimental data set. A sign test (ZAR1999) C. texanum was investigated, as these two
was performed on the resulting values. species coexist on thistle in the spring.
Histology: Plant tissue exposed to het- Voucher specimens: Specimens of the
eropteran feeding was sectioned and exam- dipteran parasitoid Trichopoda pennipesF. are
ined under a light microscope. Field collect- deposited in the California Academy of Sci-
ed plant material was supplemented by
ences, Department of Entomology. Coreid
caging bugs on potted plants and cuttings in
specimens are in the insect collection at
the laboratory. Sites of observed stylet inser-
Texas A&M University, Department of En-
tion were marked on the plant surface with
tomology.
an indelible pen. Marked plant tissue was
cut with a single edge razor blade, allowing
Results
a margin of ca. 2 mm. around the point of
insertion, and fixed in either Carnoys solu-
Field census. Although a diverse array
tion (0.5 hr) or formalin-acetic acid-alcohol
of plants from seven families served as L.
(FAA) (48 hrs). Material fixed in Carnoys
phyllopus breeding hosts at BFL (Table 1),
was dehydrated through a series of ethyl al-
plant species were not used in direct propor-
cohols to xylene, while FAA treated tissue
tion to frequency of occurrence. One species
was dehydrated with tertiary butyl alcohol,
in each study plot was always colonized to a
following the method of JOHANSEN (1940).
greater extent than predicted on the basis of
Although both procedures were satisfactory,
abundance alone, and others (e.g., grasses)
that of Johansen proved more consistently
were never used as breeding hosts at all.
reliable. Dehydrated tissue was embedded in
Temporal patterns of bug distribution on
Paraplast™and sectioned at 15 microns on
various wild and cultivated host plants are
a rotary microtome. Serial sections obtained
shown in Figure 2. Small vertical arrows in-
in this manner were rehydrated and stained
dicate the beginning of plant reproductive
with a 1 % solution of safranin in 50 %
activity. On thistle, tomato, sunflower and
ethanol, and counterstained with fast green
goldenrod, bug density increased dramati-
(0.2 % in 50 % ethanol). Best results were
cally following the transition from vegeta-
obtained using a staining schedule of 2 h in
tive to reproductive growth. Colonization
safranin solution, followed by 1 min in fast
green and 2 min in each of two 95 % alco- was concurrent with fruiting in the latter
hol baths.
Table 1: Nymphal host plants of L. phyllopus, Travis County, Texas, 1977-1979. Asterisk
After staining and subsequent dehydra- indicates observations at locations other than Brackenridge Field Station.
tion of sections, coverslips were mounted Plant family Plant species Common name
with Permount™. Bug salivary sheaths stain Asteraceae Achillea millefoliumL. yarrow
bright pink with safranin. Xylem stains red Baccharis neglectaBRITT. desert willow
Cirsium texanumBUCKL. Texas thistle
in contrast to the fast green absorbed by
Gutierrezia texana(DC) TORR. & GRAY broomweed
parenchyma and other non-lignified plant Helianthus annuusL. sunflower
tissues. Both stylet tracks and damaged Heterotheca latifoliaBUCKL. camphor weed
Solidago altissimaL. goldenrod
plant tissue were easily observed using this
Bignoniaceae Campsis radicans(L.) SEEM. trumpet creeper*
staining technique. As the plane of section-
Cucurbitaceae Cucurbita pepoL. squash
ing only rarely coincided with the path of
Lamiaceae Callicarpa americana L. French mulberry
insertion, seriality of sections was critical in
Malvaceae Hibiscus (=Abelmoschus)esculentusL. okra
determining the termination point of the
Onagraceae Gaura parvifloraDOUGL. lizard-tail
stylet tracks. Rare sections bearing com-
Orobanchaceae Agalinis heterophylla(NUTT.) SMALLEXBRITT. prairie false foxglove
plete, parallel-cut salivary sheaths were pho- Agalinis strictifolia(BENTH.) PENNELL stiffleaf false foxglove
tographed at 100x with a Nikon Eclipse Scrophulariaceae Verbascum thapsus L. woolly mullein*
E600 microscope equipped with an Olympus Solanaceae Lycopersicon esculentumMILLER tomato
DP10 digital camera. Solanum eleagnifoliumCAV. silver-leaf nightshade
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hatched prior to flowering only in 1979, and
buds were used temporarily as a food re-
source until developing seed heads became
available.
Preference among plant reproductive
structures is best documented by the de-
tailed data for C. texanumin spring of 1979
(Fig. 3). Weekly plant censuses and biweek-
ly bug counts covered the period from ap-
pearance of the first bud primordia in April
until seed set in early June. For each census
date, numerical tallies were converted to
percentages, to facilitate comparisons be-
tween plant organ availability and bug uti-
lization. Percent bug utilization was calcu-
lated as number of bugs on a given plant
structure (e.g. bud, flower, etc.) divided by
total bugs observed on reproductive organs
of that host plant species. Plant percentage
Fig. 2: Temporal patterns of L. phyllopus three species. Individuals dispersed between
distribution on various cultivated and wild host plants with overlapping life cycles, as values were determined in a similar manner.
host plants based on 1978 census counts, Preference was indicated when bug percent-
one host reached senescence and the next
Travis Co., Texas.
age use exceeded plant percentage availabil-
species began fruiting. Okra and H. latifolia
ity. Total daily bug counts during the census
become reproductive several months before
ranged from 10 to 122; plant parts counted
bug invasion, but were never colonized dur-
in each census ranged from 40 at first ap-
ing the vegetative stage. For a given plant
pearance of primordia to 302 at peak
species, bug density corresponded closely
growth.
with abundance of plants in reproductive
condition. The number of reproductive Early in the season, bugs concentrated
plants was significantly correlated with the on primordia (Fig. 3a), areas of the plant ex-
log of bug density in the study area for both hibiting rapid growth. As true buds ap-
C. texanum(r = 0.927, n = 15, P < 0.01) and peared (Fig. 3b), abrupt switching behavior
H. latifolia(r = 0.692, n = 44, P < 0.01); oth- was evident, leading to disproportionately
er plant species were not numerous enough lower use of the still common primordia.
for statistical analysis. Identical switching behavior accompanied
the first appearance of developing seed
Leaffooted bugs were active from early
heads (Fig. 3d), which continued as the pre-
spring to late fall, and overwintered as
ferred feeding site for the remainder of the
adults. Spring emergence varied from mid-
season. Flowers (Fig. 3c), occurring during
February to late March, depending on the
the same time period as immature seed
harshness of the winter. For 1976-1978,
heads, were rarely used. Ripening of seed
good correspondence was apparent between
heads in mid-June was not accompanied by
bug emergence and the condition of C. tex-
an increased proportion of bugs on mature
anum, the first breeding host. In early
heads (Fig. 3e).
spring, while thistles remained in the rosette
stage, an occasional leaffooted bug could be Similar census data for 1978 (not pre-
observed probing on B. neglecta, a woody, sented) also indicated an overwhelming
late fall host.However, large aggregations of preference for immature fruit and develop-
emerging adults did not appear in spring un- ing seed heads, and concomitant avoidance
til thistles commenced bolting and pro- of open flowers and mature fruits and seeds;
duced the first central bud primordia. Copu- this was observed for C. texanum, C. ameri-
lation began 1-3 weeks after emergence cana, H. latifolia, and S. altissimaconsistent-
from overwintering, and production of ly and for H. annuusin early season (June).
nymphs coincided with flowering and seed Mature seed heads of the last species were
development of C. texanum. Nymphs preferred in July, and all seed heads were
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© Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at
used in proportion to abundance at the end
of the season in August.
A comparison of L. phyllopus distribu-
tion with that of a less common coreid, E.
galeator, on the same host plant shows a
clear difference in utilization of plant parts
of C. texanum(Fig. 4). Significantly higher
numbers of L. phyllopusare found on repro-
ductive structures (buds, flowers, and seed
heads) compared with leaves or stems (T =
8.22, df = 2, P = 0.016), whereas signifi-
cantly more E. galeator are found on stems
(includes branches, petioles, and peduncles)
than on leaves or reproductive parts (T =
9.39, df = 2, P < 0.01).
Mark-recapture. Analysis of 1977 cap-
ture-recapture data provided information on
dispersal, longevity, copulatory activity, sex
ratio, predation, and parasitism of adults, in
addition to the primary objective of docu-
menting individual host plant shifts. For
males, 116 individuals were recaptured out
of 300 marked (38.7 %); in total, 299 recap-
ture events resulted in an average recapture
frequency of 2.58. Of 243 females marked,
86 (35.4 %) were recaptured in 153 recap-
ture events, for an average recapture fre-
quency of 1.78. Females showed a greater
tendency to disperse, although distance trav-
eled was equivalent between the sexes; 31 fe-
male dispersants (36 %) moved an average of
42.31 m, whereas for the 33 male dispersants
(28.5 %), the mean distance moved by dis-
persing individuals was 44.01 m.
The majority of individuals recaptured
(71.5 % of males, 63.9 % of females) re-
mained in a single patch of host plants.
Most dispersants were recorded moving be-
tween separate patches of the same host
plant species. However, multiple host shifts
Marked bugs were also observed in cop-
were documented. Teneral adults marked on Fig. 3: Floral and fruiting stages of Cirsium
ula. Among male L. phyllopus, eight bugs
C. texanum were subsequently recaptured texanum, Travis Co. Texas, April-June 1979,
while feeding on H. annuus(n = 4) and L. were observed to be mating on two separate showing frequency of occurrence of each
occasions. One marked individual engaged structure and distribution of L. phyllopus;
esculentum(7). One mature, fully sclerotized
squares connected by solid lines indicate
in four copulations on different days. For fe-
adult marked on G. parviflora was recap- percent occurrence of plant structure;
tured feeding on H. annuus. Mature individ- males, three individuals were seen mating circles connected by dotted lines indicate
uals marked on H. annuus were observed twice, and two engaged in copulations at percent bug distribution on a structure.
feeding on H. latifolia(2), L. esculentum(1), least three times during the course of the
and Zea mays L. (3). Marked individuals study. Since subsites were checked only
from H. latifolia fed upon G. parviflora (1), briefly each day (ca. 10 minutes per site),
and H. annuus (4), while those from L. es- these observations represent only a small
culentum dispersed to feed upon H. annuus fraction of total copulatory activity. Caged
(8). The maximal number of host shifts ob- bugs in the laboratory mated nearly every
served was four per marked adult. evening. No individuals marked as teneral
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© Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at
adults were observed in copula on C. tex- what more frequently than legs with simple
anum, but four of the 11 dispersants sighted tibiae, this trend may indicate only that
again on sunflower and tomato mated at predators preferentially approach from the
least once on the adult host plant. After rear, or that the expanded leaf-feet present a
bugs reached adulthood, average residence larger target for attack. Larger sample sizes
time on the nymphal host plant (C. tex- would be required to verify a predator escape
anum) was 3.8 +2.1 days for males (n = 18), function for the tibial expansions.
and 3.5 +2.1 days for females (n = 11).
A major natural enemy of L. phyllopusat
Field longevity (e.g., residence rate) was BFL is the tachinid fly Trichopoda pennipesF.
slightly higher for males, and the longest in- This parasitoid species (actually a complex
terval between initial marking and final re- of cryptic species or biotypes) is an impor-
capture was 51 days, as opposed to 42 for fe- tant natural enemy of the economic pest N.
males. The recapture duration decay plot viridula (JONES 1988), and leaffooted bugs
over time indicated a Type II survivorship serve as an alternative host in many crops in
pattern for both sexes. For males, the regres- the southeastern United States (TILLMAN
sion line may be expressed as y = 4.55 - 2006). Other coreid genera attacked include
0.0878x, where x = days in residence and y Acanthocephala, Anasa, Archimerus, Chelin-
= ln number of individuals (F = 1728.3; df = idea, Euthochtha, Leptoglossus, and Narnia
1, 49; P < 0.005). For females, y = 3.94 - (ARNAUD 1978). At BFL, T. pennipes has
0.0985x (F = 803.1; df = 1,40; P < 0.005). been reared from Acanthocephala declivis
SAY, A. femorata (F.), A. terminalis (DAL-
Only the sex ratio of the overwintering
LAS), Chelinidea vittiger UHLER, and Lep-
Fig. 4: Distribution of Leptoglossus generation on C. texanum was significantly
phyllopus(A) and Euthochtha galeator(B) toglossus oppositus (SAY)as well asL. phyllo-
biased toward males (s.r. = 0.602, n = 103,
on leaves, stems, and reproductive parts of pus(Mitchellunpublished).
the host plant Cirsium texanum, Travis Co., χ2= 4.28, df = 1, P < 0.05). Census data for
Texas, April-May, 1979. Median value, first 1978 corroborated this result (s.r. = 0.597, n Intensity of parasitism was estimated as
and third quartiles, and upper and lower = 613, χ2= 23.1, df = 1, P < 0.01). For five the proportion of adult bugs bearing a
ranges indicated by box and whisker plot. weeks following the initial colonization of macrotype egg (or eggs) on the exoskeleton.
the first spring host, males predominated; af- Mark-recapture data indicated that high
ter this time and throughout subsequent levels of parasitism were attained only in the
generations, the ratio of males to females overwintering and first spring generations,
did not differ significantly from 1:1. with 46 % and 27 % egg-bearing individu-
als, respectively. Leptoglossus phyllopusis the
The large hind leaf-feet of bugs in the
first hemipteran species to reach appreciably
coreine tribe Anisoscelini detach easily, and
high densities in the spring, whereas alter-
may operate as a predator escape mecha-
nate hosts (e.g., A. femorata, Anasa tristis
nism. The relative extent of predation in
(DEGEER), various pentatomid species) be-
different populations may be estimated by
come common on garden crops somewhat
frequency of leg loss, in much the same way
later in the season. According to both mark-
that tail break frequency is used to compare
recapture and census data, <10 % of L. phyl-
predation rates among lizard populations
lopusin summer and fall populations bear ta-
(e.g., PIANKA 1970). Leg loss data for indi-
chinid eggs.
viduals collected during the capture-recap-
ture study showed that only the overwinter- Oviposition site on the bug exoskeleton
ing generation on C. texanum exhibited a varies, but most eggs are placed on the head
high rate of leg loss: 65 % of individuals re- of L. phyllopus. Of 142 eggs examined, dis-
mained intact (n = 100). In all subsequent tribution on the body was as follows: head,
generations, the percentage of undamaged 72.5 %; pronotum, 13.4 %; elsewhere on
individuals was considerably higher, ranging thorax, 9.9 %; abdominal sternites, 2.1 %;
from 87.0-90.3 % (n ≥ 93). Summation of abdominal tergites, 0.0 %; tibial foliation,
hind, mid, and foreleg loss frequency over 0.7 %; wing, 1.4 %. The presence of a ta-
the entire season yields 55 individuals lack- chinid egg on the exoskeleton does not ap-
ing at least one hind leg, 41 lacking a mid- pear to deter an ovipositing T. pennipes. Oc-
dle leg and 13 with a detached foreleg. Al- currence of supernumerary T. pennipeseggs,
though the foliated hind legs are lost some- although infrequent in females, was com-
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