Labidomera Clivicollis Research Articles

Does secretory canal architecture determine the sabotage behaviors of insect folivores?

Insect folivores on plants protected by secretory canals commonly sever leaf veins or cut trenches before feeding beyond the cuts. Previous studies reported that vein cutting occurs when canals have an arborescent arrangement, whereas trenching is found when canals have a net-like arrangement. However, some danaine species, such as the monarch caterpillar, Danaus plexippus, show both behaviors on the same milkweed plant; early instars cut circular trenches and later instars chew furrows in the leaf midrib. This study tests the hypothesis that milkweed canals differ in arrangement at different scales, thus requiring different behaviors from early and late instars. I compared common milkweed, Asclepias syriaca (Apocynaceae) with prickly lettuce, Lactuca serriola (Asteraceae). Leaves were damaged with standard wounds and the response of the laticifers was compared by measuring latex exudate. With L. serriola, severing either the primary or secondary veins failed to reduce latex emission beyond the cuts. The veins and associated laticifers form an interconnected network; plusiine caterpillars on L. serriola disarm the network with a trench. With A. syriaca, transecting the midrib virtually eliminated distal exudation. However, severing a secondary vein caused only a partial reduction. To decrease exudation beyond secondary veins, milkweed insects need either to sever multiple adjacent veins (as shown by Labidomera clivicollis beetles) or to cut a trench (as in early instar danaine larvae). Thus, in both A. syriaca and L. serriola, herbivore behaviors match the laticifer systems as predicted by the hypothesis that canal architecture has a central role in determining behavior.

Above‐ground herbivory by red milkweed beetles facilitates above‐ and below‐ground conspecific insects and reduces fruit production in common milkweed

Summary Initial herbivory and induced plant responses can influence subsequent above‐ and below‐ground herbivore attack. When two life stages of the same herbivore damage different plant parts sequentially, there is strong potential for plants to respond with induced plant defence against the later attacker. Alternatively, the earlier attacker could manipulate the host plant to facilitate the later‐feeding life stage. We studied herbivory by foliage‐feeding adults and root‐feeding larvae of the red milkweed beetle (Tetraopes tetraophthalmus) on native common milkweed (Asclepias syriaca) in laboratory and field experiments. We applied factorial above‐ and below‐ground herbivory treatments to test for induced responses, effects on later‐feeding conspecific larvae, and damage by naturally colonizing herbivores, including adult T. tetraophthalmus. We found that the inducibility of toxic cardenolides was systemic across the root–shoot barrier, with the highest concentrations in plants damaged both above‐ and below‐ground. Initial above‐ground herbivory increased root damage and larval survival, suggesting an increase in root quality following leaf herbivory. Initial below‐ground herbivory did not affect the performance of later‐feeding larvae, indicating limited importance of induced root cardenolides and competition between clutches of T. tetraophthalmus. In a natural milkweed population, initial above‐ground herbivory attracted conspecific adults and milkweed leaf beetles (Labidomera clivicollis) and ultimately reduced fruit production by 33%. Nonetheless, the probability of damage by monarch caterpillars (Danaus plexippus) was reduced on plants initially damaged by T. tetraophthalmus above‐ground, likely due to reduced oviposition following induced plant responses. Synthesis. Induced plant responses of common milkweed to above‐ground damage by adult T. tetraophthalmus both facilitate further damage by adults and enhance the performance of their root‐feeding larvae, most likely as a result of host plant manipulation. Although the same induction reduced monarch herbivory, the net effect of these interactions was negative for the plant as fruit production was substantially reduced. These results imply that host plant manipulation may be especially common by specialist herbivores that have sequential above‐ and below‐ground life stages.

Community-wide convergent evolution in insect adaptation to toxic cardenolides by substitutions in the Na,K-ATPase

The extent of convergent molecular evolution is largely unknown, yet is critical to understanding the genetics of adaptation. Target site insensitivity to cardenolides is a prime candidate for studying molecular convergence because herbivores in six orders of insects have specialized on these plant poisons, which gain their toxicity by blocking an essential transmembrane carrier, the sodium pump (Na,K-ATPase). We investigated gene sequences of the Na,K-ATPase α-subunit in 18 insects feeding on cardenolide-containing plants (spanning 15 genera and four orders) to screen for amino acid substitutions that might lower sensitivity to cardenolides. The replacement N122H that was previously shown to confer resistance in the monarch butterfly (Danaus plexippus) and Chrysochus leaf beetles was found in four additional species, Oncopeltus fasciatus and Lygaeus kalmii (Heteroptera, Lygaeidae), Labidomera clivicollis (Coleoptera, Chrysomelidae), and Liriomyza asclepiadis (Diptera, Agromyzidae). Thus, across 300 Myr of insect divergence, specialization on cardenolide-containing plants resulted in molecular convergence for an adaptation likely involved in coevolution. Our screen revealed a number of other substitutions connected to cardenolide binding in mammals. We confirmed that some of the particular substitutions provide resistance to cardenolides by introducing five distinct constructs of the Drosophila melanogaster gene into susceptible eucaryotic cells under an ouabain selection regime. These functional assays demonstrate that combined substitutions of Q(111) and N(122) are synergistic, with greater than twofold higher resistance than either substitution alone and >12-fold resistance over the wild type. Thus, even across deep phylogenetic branches, evolutionary degrees of freedom seem to be limited by physiological constraints, such that the same molecular substitutions confer adaptation.

Ambulatory Use of Ventro-Lateral Abdominal Ampullae by Larvae of Labidomera clivicollis(Kirby) (Coleoptera: Chrysomelidae: Chrysomelinae)

Abstract Ampullae appear to be common in the larvae of some chrysomelid subfamilies. We describe and discuss the occurrence and use of these structures in larvae of Labidomera clivicollis (Kirby), on its host plant Asclepias verticillata L. (Asclepiadaceae) under field and lab conditions. Through film footage, we reveal that ventral ampullae are apparent on all ten segments of the larval abdomen; however, only those associated with segments AVIII–AX were actually used in ambulation by anchoring to the host plant. These ampullae always function with the true legs during movement. Our study unveils ambiguities in homology and terminology of abdominal ambulatory structures that are relevant to discussions of chrysomelid characters and phylogeny.

COMMUNITY-WIDE IMPACTS OF HERBIVORE-INDUCED PLANT RESPONSES IN MILKWEED (ASCLEPIAS SYRIACA)

The effects of early-season herbivory and subsequent induced plant responses have the potential to affect the diversity of herbivorous insect communities. We investigated the seasonal development of the herbivore fauna on common milkweed (Asclepias syriaca) to understand the effect of early-season herbivory by different species on insect growth, natural colonization, and community composition. First, we showed that damage by an early-season stem-feeding weevil (Rhyssomatus lineaticollis) reduced growth of monarch larvae (Danaus plexippus) and leaf beetle larvae (Labidomera clivicollis), suggesting that plant quality is reduced by weevil damage. To better understand the potential for initial herbivore damage to affect subsequent colonization by herbivores in the field, we compared undamaged controls to plants experimentally damaged with one of three herbivores: weevils, monarchs, or leaf beetles. We counted seven species of naturally colonizing herbivores on all plants for the next two months to assess colonization, damage, and insect community richness. Our results showed that initial herbivory by different species altered host plant use by herbivores in two years of experiments. Similarly, induced resistance and suscep- tibility occurred in both years, but due to different initial damaging species on individual plants. Treatment effects also scaled up to alter herbivore community richness. Initial treatments varied in their persistence through the season. For example, in 2001, the influence of initial monarch damage dissipated due to subsequent damage by colonizing herbivores, but the impacts of initial weevil treatment were unaffected. This result suggests that, al- though induced responses to weevil feeding persisted through the season, monarch herbivory was more likely to affect the herbivore community via a cascade of indirect effects. In 2002, plant and insect responses were more specific, depending on the identity of both initial and colonizing herbivore species. Despite year-to-year variation, considerable con- sistency in many responses to our treatments indicates that the identity of the initially colonizing herbivore can affect subsequent plant use and community structure. Given the preponderance of influential early-season herbivores, the effects of induced plant responses similar to those presented here may be widespread and may strongly contribute to the structure of phytophagous insect communities.

Specificity of induced plant responses to specialist herbivores of the common milkweed Asclepias syriaca

Induced plant responses to herbivory appear to be universal, yet the degree to which they are specific to sets of herbivores is poorly understood. The generalist/specialist hypothesis predicts that generalist herbivores are more often negatively affected by host plant defenses, wheras specialists may be either unaffected by or attracted to these same “plant defenses”. Therefore, specialists should be less predictable than generalists in their responses to induced plant resistance traits. To better understand the variation in plant responses to herbivore attack, and the impacts these responses have on specialist herbivores, we conducted a series of experiments examining pairwise interactinos between two specialaist herbivores of the common milkweed (Asclepias syriaca). We damaged plants mechnically, with swamp milkweed beetles (Labidomera clivicollis), or with monarchs (Danaus plexippus), and then asessed specificity of elicitation, both by measuring a putative defensive trait (latex volume) and by challenging plants with insects of both species in bioasays. Latex production increased by 34% and 13% following beetle and monarch herbivory, respectively, but only beetles significantly elevated latex production compared to undamaged controls. While beetle growth was negatively affected by latex across all experiments, beetles were not affected by previous damage caused by conspecifies or by monarchs. In contrast, monarchs feeding on previously damaged plants were 20% smaller, and their response was the same on plants damaged mechnically or by either herbivore. Therefore, these specialist herbivores exhibit both specificity of elicitation in plant responses and specificity of effects in response to prior damage.

Sexually transmitted parasites and sexual selection in the milkweed leaf beetle, Labidomera clivicollis

Milkweed leaf beetles (MLBs; Labidomera clivicollis Chrysomelidae) are parasitized by a subelytral mite, Chrysomelobia labidomerae (Tarsonemina: Podapolipidae). We show that C. labidomerae is transmitted between MLBs when they copulate, and can reduce the survival of nutritionally stressed beetles. We investigated the effect of this sexually transmitted parasite on mate choice and male‐male competition in MLBs, and the consequences of variation in these behaviours for mite transmission. We found no evidence of parasite avoidance by MLBs, and evidence for high rates of parasitism in the MLB populations we surveyed. In the absence of females, parasitized males contacted unparasitized males more often and for longer than controls, and they tended to displace rival males from females more often than did unparasitized males, a result consistent with the interpretation that parasitized beetles compensate for loss of fitness by increasing reproductive effort. These changes can also benefit mites, because longer and possibly more contacts between beetles provide more opportunities for transmission, but there is no evidence that these changes in male behaviour result from parasite manipulation.

Egg cannibalism by larvae and adults of the milkweed leaf beetle (Labidomera clivicollis, Coleoptera: Chrysomelidae)

Abstract. Egg cannibalism is a form of infanticide that has been implicated in the evolution of guarding of eggs and immatures in some species of insects. The milkweed leaf beetle, Labidomera clivicollis (Coleoptera: Chrysomelidae), exhibits three types of egg cannibalism in the field: siblicide, cannibalism of eggs by older larvae from earlier hatching egg clutches, and cannibalism of eggs by adult females. Unlike their close relative, L.suterella (Choe, 1989), female L.clivicollis do not guard their eggs or immatures. They move slowly about a patch of milkweeds laying multiple egg clutches. First instar and older larvae cannibalized eggs in two geographically separated study populations (subspecies) in Austin, Texas, and Bridgeport, New York, U.S.A. Although adult females of both populations cannibalized eggs in the laboratory, only the Texas subspecies, L.c.rogersii, exhibited such cannibalism in the field. In the field, correlates of siblicide varied both temporally (within subspecies) and spatially (between subspecies) in terms of whether they were statistically significant, but trends were all in the same direction. Group size was positively correlated with hatching success and siblicide, but negatively correlated with other types of predation. Siblicide was also positively correlated with egg density in a laboratory study of the Texas subspecies, L.c.rogersii. In the laboratory, an average of 15–17% of L.c.clivicollis eggs never developed embryos. Although these were almost always cannibalized, some viable eggs were also eaten and there is no evidence that females increased the proportion of infertile eggs they laid to increase siblicide. Field data and laboratory experiments showed that adult female L. c.rogersii cannibalized eggs while males rarely did. Females preferentially ate the eggs of other females over their own eggs in an experiment that removed spatial cues. Although the selective context of cannibalism is not demonstrated here, I suggest that females may increase siblicide by increasing egg density and may cannibalize eggs to protect their own eggs from being eaten by second and third instar larvae produced by other females.

Scramble competition polygyny in the milkweed leaf beetle: combat, mobility, and the importance of being there

Scramble competition polygyny in the milkweed leaf beetle: combat, mobility, and the importance of being there

Population dynamics ofChrysomelobia labidomeraeEickwort, a parasite of the Colorado potato beetle

Abstract The population dynamics of Chrysomelobia labidomerae Eickwort, a podapolipid parasite of the Colorado potato bettle (CPB), Leptinotarsa decemlineata (Say) in Mexico; and the milkweed leaf beetle (MLB), Labidomera clivicollis (Kirby) in the U.S. and Canada; was studied in the laboratory and in field cages in Rhode Island. Optimal development and survival occurred at 30° C with a generation time of 14.2 days. Mites collected from the MLB host in R.I. developed more slowly and had poorer survival on the CPB than mites originally collected from the CPB. Dispersal of C. labidomerae (primarily preoviposition females) occurred during beetle copulation and was dependent upon beetle age and temperature. C. labidomerae could survive the winter in Rhode Island.

Behavior ofChrysomelobia labidomeraeEickwort parasitizing the Colorado potato beetle

Abstract Investigations on niche selection, migration, and oviposition behavior were conducted with Chrysomelobia labidomerae Eickwort parasitizing the Colorado potato beetle, Leptinotarsa decemlineata (Say). These findings were compared with those of Baker and Eickwart for the behavior of C. labidomerae on the milkweed leaf beetle, Labidomera clivicollis (Kirby). The most consistent difference is that adult female mites of the milkweed leaf beetle race are found on the exterior surface of C. labidomerae more often than the Colorado potato beetle mite race. Observations on individual mites throughout their development revealed a regular pattern of migration from one stage-specific niche to the next. The routes of migration are illustrated for each developmental stage. Studies on oviposition behavior provided no evidence for a diel periodicity in egg laying. The niche occupied by eggs is a result of a “rolling” behavior by adult female mites.

Determinants of paternity in the milkweed leaf beetle

Males and females of the milkweed leaf beetle mate for up to 2.5 d in the field; copulation is interspersed with mounted courtship behavior and periods of passive riding on the female's back. In 1985, females mated with up to 10 different males in Bridgeport, New York, and matings averaged 0.75±0.04 (SE) d in duration. Sperm utilization patterns are complex in the milkweed leaf beetle. In the laboratory, mating duration, mating order and the duration of the gap between matings affected paternity. The second male's sperm predominated when a female's two consecutive matings were of equal duration (but were long: 45 h each) or when they were intermediate in duration (15 h each) with a 5 day gap between the two matings. The mechanism of sperm predominance appears to be one of time-dependent sperm removal and replacement. Neither relative nor absolute size of males affected the extent to which they superceded the sperm of rivals. Electrophoretic analysis of paternity at 6 polymorphic loci showed that offspring of at least eight out of 11 mating pairs pairs collected in the field at the end of the 1984 breeding season were sired by more than one male. At least seven of the 11 families produced some offspring that were sired by the female's most recent mate in the field and in no case was the collected male completely excluded from paternity. In a greenhouse plot, males climbed off females' backs a mean of 1.1±0.3 h before oviposition. Females did not oviposit with males on their backs and did not oviposit sooner when males were removed than when males were allowed to remain mounted, indicating that males don't keep females from ovipositing until they can achieve sperm predominance. The close concordance between male disembarkment and oviposition suggests that males remain with females beyond the time when they have superceded the sperm of their prior mates, possibly to guard them from rival males. Although the prolonged mating association of the milkweed leaf beetle cannot be separated into discrete copulatory and guarding phases, the results of this study suggest that prolonged mating enables males both to remove and replace the sperm of the females' prior mates with their own sperm and to prevent females from remating prior to oviposition.

Effects of parasitism by the miteChrysomelobia labidomerae(Acari: podapolipidae) on the longevity and fecundity of its host beetle,labidomera clivicollis(coleoptera: chrysomelidae)

Abstract Under laboratory conditions, parasitism by Chrysomelobia labidomerae did not significantly reduce the longevity, total fecundity, and daily oviposition rate of New York milkweed leaf beetles, Labidomera clivicollis.

Prolonged mating in the milkweed leaf beetle Labidomera clivicollis clivicollis (Coleoptera: Chrysomelidae): a test of the “sperm-loading” hypothesis

Female milkweed leaf beetles (Labidomera clivicollis clivicollis) frequently mate with more than one male, and pairs form mating associations which last for up to 42 h in the field. I tested the hypothesis that males remaining with females for long periods of time benefit by numerically overwhelming the sperm of their competitors. Male L.c.clivicollis copulated intermittently with females throughout an 11 hour period in the laboratory. When virgin females were allowed a single copulation, 94.3% of the sperm they received were located in the spermatheca immediately afterward. Males were not sperm-depleted, for they had large numbers of sperm available after one copulation (mean=230,000±43,200); the maximal number of sperm a male transferred to a female in 24 h was 30,500. There was a positive linear relationship between the number of sperm transferred and time up to 24 h after mounting (r2=0.178, P<0.003). These data suggest that males transfer increasing numbers of sperm throughout a 24-h-period. Mating duration was the most important determinant of paternity when females were placed with one male for 24 h and another male for 6 hours. Females whose first matings were longer showed first male sperm predominance (as determined by starch-gel electrophoresis), while females whose second matings were longer showed last male sperm predominance. In view of these data, it is puzzling that males do not inseminate with large numbers of sperm immediately after mounting the female. It is possible that female refractory behaviors make insemination difficult and favor prolonged mating by male milkweed leaf beetles.

Life-history Consequences of Body-size Variation in the Milkweed Leaf Beetle, Labidomera clivicollis (Coleoptera: Chrysomelidae)

Adult body size of milkweed leaf beetles, Labidomera clivicollis rogersii (LeConte), varied greatly among beetles given different amounts of food in the last larval stadium. Larger females laid approximately twice as many eggs as did smaller females, regardless of whether they reproduced before or after diapause, or were maintained on unlimited or limited regimens of food availability. Age at first reproduction was significantly delayed among smaller females when adults were maintained on the limited food regimen. Eggs from larger females were heavier and resulted in higher larval survivorship to pupation than eggs from smaller females. Larger adult beetles survived total starvation nearly twice as long as smaller beetles, but adult size had no consistent effects on survival through summer or winter in outdoor cages.

Host specificity tests ofChrysomelobia labidomerae,a mite parasitic on the Colorado potato beetle

Abstract The parasitic mite, Chrysomelobia labidomerae Eickwort, appears to be limited to coleopterous hosts in the tribe Zygogrammini of the subfamily Chrysomelinae. The mite was originally described as a parasite of adult Labidomera clivicollis (Kirby) in New York. We found it in Mexico parasitizing 4 additional species in the tribe Zygogrammini: Leptinotarsa decemlineata (Say), Leptinotarsa undecemlineata Stahl., Leptinotarsa signaticollis Stahl., and Leptinotarsa cacica Stahl. Experimentally, we found many species to be unsuitable hosts for a Mexican race of the mite including the honey bee, Apis mellifera (L.); coccinellids: Hippodamia convergens Guerin-Meneville, Coleomegilla maculata (DeGeer), Coccinella septempunctata L., and the Mexican bean beetle, Epilachna varivestis Mulsant; carabids: Harpalus pennsylvanicus DeGeer, and Clivinia impressifrons LeConte; the cerambycid, Tetraopes tetrophthalmus (Forster); and the chrysomelid, Lema trilineata L. Larvae of L. decemlineata were also found to be uns...

Phenology and Dormancy in the Milkweed Leaf Beetle Labidomera clivicollis (Kirby)

Phenology and Dormancy in the Milkweed Leaf Beetle Labidomera clivicollis (Kirby)

Environmental Determinants of Seasonal Body Size Variation in the Milkweed Leaf Beetle, Labidomera clivicollis (Kirby) (Coleoptera: Chrysomelidae)

Milkweed leaf beetles, Labidomera clivicollis (Kirby), eclosing later in the fall in central Texas have smaller adult sizes. Laboratory studies show that this seasonal decline is more probably due to deteriorating larval food supplies than to decreasing temperature, decreasing photoperiod, or maternal effects on egg weight. Adult size can vary greatly, because larvae in the last stadium become competent to metamorphose at weights much lower than those normally attained under favorable nutritional conditions. Because Labidomera can diapause only in the adult stage, the ability to complete development at low larval weights should be adaptive when the environment becomes increasingly foodand time-limited.

Photoperiodic control of reproduction in the milkweed leaf beetle, Labidomera clivicollis

ABSTRACT. Photoperiod significantly affected reproduction in a central Texas population of the milkweed leaf beetle Labidomera clivicollis (Kirby) (Chrysomelidae). Laboratory reared beetles responded to a critical photoperiod of LD 12.5: 11.5; longer photoperiods induced reproduction, while shorter photoperiods induced diapause. Both larval and adult stages exhibited sensitivity to photoperiod. Beetles exposed to long days as adults reproduced regardless of photoperiod experienced as larvae. However, exposure to long days, as larvae but short days as adults also induced reproduction in an intermediate portion of the population. No larval instar appeared to be more sensitive than the others, and the proportion of the population responding did not increase with cumulative larval exposure to long days. Larval sensitivity to photoperiod may be ecologically significant to central Texas populations because it permits a substantial portion of the autumn generation to initiate a third generation in favourable years.

Photoperiodic effect on size‐related metamorphosis in the milkweed leaf beetle, Labidomera clivicollis

ABSTRACT. Photoperiod significantly affected size‐related aspects of metamorphosis in the milkweed leaf beetle Labidomera clivicollis (Kirby) (Chrysomelidae). Larvae reared under short‐day photoperiod successfully pupated at lower weights than larvae reared under long‐day photoperiods. This short‐day effect was observed to an equivalent extent in both males and females; but within photoperiod treatments, males consistently pupated at lower weights than females. It is likely that the short‐day effect on metamorphosis is associated with photo‐periodically induced changes in larval corpora allata activity or juvenile hormone titre. Ecologically, the short‐day effect on metamorphosis may enhance the moulting success of larvae which encounter food shortages during autumn.