Beetle Feeding Research Articles

Timing of oviposition enables dominant female burying beetles to destroy brood-parasitic young

Infanticide can increase an individual’s reproductive success through reduced competition for its offspring. Here we document the occurrence and effects of infanticidal behaviour by dominant female burying beetles, Nicrophorus vespilloides, in nontolerant breeding associations. Burying beetles feed and guard their young on buried carcasses, and on small carcasses, conspecific females engage in intense aggression. Dominants largely exclude subordinates from the carcass and are the sole caregivers for the larvae. Although subordinates and dominants produce similar egg clutches, only one out of five surviving offspring is the subordinate’s. We hypothesized that much of this skew is due to temporally cued infanticide by dominants. Females oviposit over the course of 24–48 h, and kill larvae they encounter prior to the hatching of their own larvae. Such infanticide can lead to significant skew only if the dominant’s larvae hatch significantly later than the subordinate’s, and if more subordinate than dominant larvae hatch during the infanticidal phase. The subordinate’s share of larvae hatching during the parental phase must be smaller than her share of eggs, and the portion of subordinate larvae killed by the dominant should increase with an increasing difference in oviposition time between the two females. These predictions were met. Dominant females, who had exclusive access to the carcass and larvae, were able to use temporal cues to destroy over half of the subordinates’ first-instar larvae. This is the first study to unambiguously document the primary mechanism underlying reproductive dominance in nontolerant associations of female N. vespilloides.

Adults of European ant‐like stone beetles (Coleoptera: Staphylinidae: Scydmaeninae) Scydmaenus tarsatus Müller & Kunze and Scydmaenus hellwigii (Herbst) prey on soft‐bodied arthropods

AbstractScydmaenine beetles are commonly described as predators specialized in capturing and feeding on armored mites of the order Oribatida, and documented cases of feeding on other live arthropods have not been known. Based on laboratory observations and a broad choice of Acari (armored and soft‐bodied) and other soil arthropods, food preferences and associated behavior of two scydmaenine species are clarified and described. Adults of Scydmaenus tarsatus ignored oribatid and mesostigmatan mites, but readily attacked and fed on a soft‐bodied Rhizoglyphus sp. (Acaridae), and on small springtails, especially on Ceratophysella denticulata (Hypogastruridae). A water drinking behavior was observed for this species, not reported previously in any Staphylinidae. Scydmaenus hellwigii ignored all tested Acari (including Rhizoglyphus) and scavenged on dead neanurine collembolans or freshly cut pieces of large springtails; a long term culture was maintained by feeding beetles with isotomid springtails. Previously reported strict specialization of Scydmaenus as a predator on Oribatida was not confirmed and it is concluded that the studied species feed on live soft‐bodied organisms and scavenge on dead arthropods.

Plant-mediated effects of different Salix species on the performance of the braconid parasitoid Perilitus brevicollis

The blue willow beetle, Phratora vulgatissima, is considered to be the most damaging herbivorous pest in Salix short-rotation coppices throughout Europe. The braconid parasitoid Perilitus brevicollis is an important natural enemy of Phratora. As several different Salix species are used in coppices, I investigated the bottom–up (tritrophic) effects of Salix on the parasitoid. Three host plants were studied: the introduced fast-growing S. viminalis, which is highly susceptible to the beetle; S. dasyclados, which is introduced and moderately-resistant to the beetle; and the native slow-growing Salix cinerea, which is not currently used in coppices. The identity of the host-plant species had significant effects on parasitoid larval development time; parasitoids developed rapidly on the susceptible S. viminalis and slowly on the moderately resistant S. dasyclados. Increased development time resulted in reduced adult longevity. Host-plant species identity also affected larval survival; 57%, 64%, and 49% of the parasitoids successfully completed larval development in beetles fed S. viminalis, S. cinerea, and S. dasyclados, respectively. Parasitoid development was also correlated with the body size of their beetle host, but this effect was independent of the identity of the host-plant species. The results of this study suggest that the parasitoid has higher survival and growth rates when it parasitizes beetles feeding on the common coppice species S. viminalis, but the performance of the parasite is reduced when the beetle feeds on the moderately-resistant S. dasyclados. Conversely, the omnivorous biocontrol agents sometimes used in these systems appear to perform better on S. dasyclados compared to S. viminalis. The results of this study suggest that Perilitus parasitoids and omnivorous beetle predators may provide complementary protection to Salix and therefore be useful in coppice management.

New record of predatory ladybird beetle (Coleoptera, Coccinellidae) feeding on extrafloral nectaries

New record of predatory ladybird beetle (Coleoptera, Coccinellidae) feeding on extrafloral nectaries. Feeding by Exoplectra miniata (Germar) on extrafloral nectaries of Inga edulis Mart. was observed in Nova Friburgo, Rio de Janeiro, Brazil. This is the first record of this behavior for Exoplectrini.

Olfactory cues from plants infected by powdery mildew guide foraging by a mycophagous ladybird beetle.

Powdery mildews (Erysiphales) are economically important plant pathogens that attack many agricultural crops. Conventional management strategies involving fungicide application face challenges, including the evolution of resistance and concerns over impacts on non-target organisms, that call for investigation of more sustainable alternatives. Mycophagous ladybird beetles (Coleoptera: Coccinellidae) feed on powdery mildew and have considerable potential as biological control agents; however, the foraging ecology and behavior of these beetles is not well understood. Here we document the olfactory cues presented by squash plants (Cucurbita moschata) infected by powdery mildew (Podosphaera sp.) and the behavioral responses of twenty-spotted ladybird beetles (Psyllobora vigintimaculata) to these cues. Volatile analyses through gas chromatography revealed a number of volatile compounds characteristic of infected plants, including 3-octanol and its analogues 1-octen-3-ol and 3-octanone. These compounds are typical “moldy” odorants previously reported in volatiles collected from other fungi. In addition, infected plants exhibited elevated emissions of several compounds also observed in collections from healthy leaves, including linalool and benzyl alcohol, which are reported to have anti-fungal properties. In Y-tube choice assays, P. vigintimaculata beetles displayed a significant preference for the odors of infected plants compared to those of healthy plants. Moreover, beetles exhibited strong attraction to one individual compound, 1-octen-3-ol, which was the most abundant of the characteristic fungal compounds identified. These results enhance our understanding of the olfactory cues that guide foraging by mycophagous insects and may facilitate the development of integrated disease-management strategies informed by an understanding of underlying ecological mechanisms.

Evaluation of Cucurbitacin-Based Gustatory Stimulant to Facilitate Cucumber Beetle (Coleoptera: Chrysomelidae) Management With Foliar Insecticides in Melons

The bitter plant-derived compounds cucurbitacins are known to stimulate feeding of adult cucumber beetles (Coleoptera: Chrysomelidae). A cucurbitacin-based gustatory stimulant applied as a flowable bait combined with either spinosad or carbaryl was compared with foliar sprays of spinosad and carbaryl for controlling two cucumber beetle species (Diabrotica undecimpunctata undecimpunctata Mannerheim and Acalymma trivittatum Mannerheim) in honeydew melons (Cucumis melo L.). Field studies were conducted on the University of California-Davis plant pathology farm in 2008 and 2009. Beetle densities after applications and fruit damage from beetle feeding were compared among treatments. In addition, beetle survival was compared within field cages placed over the treated foliage infested with beetles. Using all three measures of efficacy, we determined that the addition of cucurbitacin bait had no effect on the level of cucumber beetle control with carbaryl in either 2008 or 2009. In both years, spinosad did not significantly reduce cucumber beetle densities in either field cages or field plots and did not reduce fruit damage relative to the untreated control. The addition of the bait to spinosad did not improve its efficacy. A laboratory bioassay of the spinosad formulation used in the field showed it had significant lethal effects on adults of both cucumber beetle species. Results indicated that the bait formulation used did not improve cucumber beetle control but may benefit from the addition of floral attractants or using a different type of cucurbitacin.

No evidence for a Ganoderma spore dispersal mutualism in an obligate spore-feeding beetle Zearagytodes maculifer

The role of spore dispersal mutualism remains equivocal in many fungus–insect assemblages. We tested experimentally whether an obligate spore-feeding beetle Zearagytodes maculifer has a mutualistic relationship with its host bracket fungus Ganoderma cf. applanatum via spore dispersal. We asked three specific questions: (1) whether or not Ganoderma spore germination rate is increased via beetle digestive activity and (2) is dependent on temperature and sporocarp identity. Spore germination rates were examined in 2 × 3 × 2 factorial experiments (spores consumed by beetles or not × temperature 20, 25, and 30 °C × two independent pairs of sporocarp–beetle populations) replicated five times in an array of 60 experimental cultures. Analysis showed that consumption by beetles significantly reduced germination rate of Ganoderma spores. The effect of temperature was modulated by the effect of individual sporocarp, and was overridden by beetle feeding. Microscopic analysis revealed that spores from beetle faecal pellets exhibited extensive damage to their thin outer walls (pellicles) and thick inner walls, as well as significant loss of cytoplasm, while control spores were intact. The overall evidence argued against our spore dispersal mutualism hypothesis, suggesting that Z. maculifer can potentially exert a negative, if vanishingly small, fitness effect on its host fungus G. cf. applanatum.

Two Genera of Aulacoscelinae Beetles Reflexively Bleed Azoxyglycosides Found in Their Host Cycads

Aulacoscelinae beetles have an ancient relationship with cycads (Cycadophyta: Zamiaceae), which contain highly toxic azoxyglycoside (AZG) compounds. How these "primitive" leaf beetles deal with such host-derived compounds remains largely unknown. Collections were made of adult Aulacoscelis appendiculata from Zamia cf. elegantissima in Panama, A. vogti from Dioon edule in Mexico, and Janbechynea paradoxa from Zamia boliviana in Bolivia. Total AZG levels were quantified in both cycad leaves and adult beetles by high performance liquid chromatography (HPLC). On average, cycad leaves contained between 0.5-0.8% AZG (frozen weight, FW), while adult beetles feeding on the same leaves contained even higher levels of the compounds (average 0.9-1.5% FW). High AZG levels were isolated from reflex bleeding secreted at the leg joints when beetles were disturbed. Nuclear magnetic resonance and mass spectroscopy identified two AZGs, cycasin and macrozamin, in the reflex bleeding; this is the first account of potentially plant-derived compounds in secretions of the Aulacoscelinae. These data as well as the basal phylogenetic position of the Aulacoscelinae suggest that sequestration of plant secondary metabolites appeared early in leaf beetle evolution.

Re‐establishment of biting mouthparts in desert‐living dung beetles (Scarabaeidae: Scarabaeinae) feeding on plant litter—Old structures reacquired or new ones evolved?

Evolution of mouthparts in adult dung beetles (Scarabaeidae: Scarabaeinae) for eating moist, fresh dung was linked with a loss of the ability to chew. However, the desert-living genus Pachysoma, probably evolved from a wet-dung feeding, Scarabaeus-like ancestor, has switched to a diet of dry fecal pellets (of rodents or small ruminants) and plant litter that requires re-establishment of chewing. Indeed, gut contents of a litter-feeding Pachysoma species indicate efficient food comminution. Based on scanning electron microscopy, cutting and grinding mouthpart structures in six Pachysoma species, of two lineages and with different food preferences, are described and compared with homologous structures in wet-dung feeding Scarabaeus species. In Pachysoma, cutting and breaking of large food items is probably performed by a clypeal scraper, a prominent epipharyngeal tooth and large maxillary galeal hooks. Further comminution is achieved by a large, grinding area evolved on the mandibular molae. Interspecific differences and the probable function and evolution of these structures are discussed. Particularly, the unique tools for cutting/breaking are completely novel structures and not results of some reacquisition of normal biting mouthparts.

Trees wanted--dead or alive! Host selection and population dynamics in tree-killing bark beetles.

Bark beetles (Coleoptera: Curculionidae, Scolytinae) feed and breed in dead or severely weakened host trees. When their population densities are high, some species aggregate on healthy host trees so that their defences may be exhausted and the inner bark successfully colonized, killing the tree in the process. Here we investigate under what conditions participating with unrelated conspecifics in risky mass attacks on living trees is an adaptive strategy, and what this can tell us about bark beetle outbreak dynamics. We find that the outcome of individual host selection may deviate from the ideal free distribution in a way that facilitates the emergence of tree-killing (aggressive) behavior, and that any heritability on traits governing aggressiveness seems likely to exist in a state of flux or cycles consistent with variability observed in natural populations. This may have implications for how economically and ecologically important species respond to environmental changes in climate and landscape (forest) structure. The population dynamics emerging from individual behavior are complex, capable of switching between “endemic” and “epidemic” regimes spontaneously or following changes in host availability or resistance. Model predictions are compared to empirical observations, and we identify some factors determining the occurrence and self-limitation of epidemics.

Beetle (Coleoptera: Scirtidae) Facilitation of Larval Mosquito Growth in Tree Hole Habitats is Linked to Multitrophic Microbial Interactions

Container-breeding mosquitoes, such as Aedes triseriatus, ingest biofilms and filter water column microorganisms directly to obtain the bulk of their nutrition. Scirtid beetles often co-occur with A. triseriatus and may facilitate the production of mosquito adults under low-resource conditions. Using molecular genetic techniques and quantitative assays, we observed changes in the dynamics and composition of bacterial and fungal communities present on leaf detritus and in the water column when scirtid beetles co-occur with A. triseriatus. Data from terminal restriction fragment polymorphism analysis indicated scirtid presence alters the structure of fungal communities in the water column but not leaf-associated fungal communities. Similar changes in leaf and water bacterial communities occurred in response to mosquito presence. In addition, we observed increased processing of leaf detritus, higher leaf-associated enzyme activity, higher bacterial productivity, and higher leaf-associated fungal biomass when scirtid beetles were present. Such shifts suggest beetle feeding facilitates mosquito production indirectly through the microbial community rather than directly through an increase in available fine particulate organic matter.

Sequestration of Camptothecin, an Anticancer Alkaloid, by Chrysomelid Beetles

Camptothecin (CPT), a monoterpene indole alkaloid, is a potent inhibitor of eukaryotic toposiomerase-I. Several derivatives of CPT are in clinical use against ovarian and lung cancers. CPT has been reported from several plant species belonging to the order Asterids, with the highest concentration in Nothapodytes nimmoniana (family Icacinaceae). In this paper, we report an intriguing observation of chrysomelid beetles (Kanarella unicolor Jacobby) feeding on the leaves of N. nimmoniana without any apparent adverse effect. LC-MS/MS analysis of the beetles indicated that 54.9% of the ingested CPT's was recovered from the wings, followed by lesser amounts in the head and abdomen. LC-HRMS analysis revealed that most of the CPT in the insect body was in the parental form available in the plants without any major metabolizable products, including sulfated and glucuronilated forms. The mechanism by which the beetles are able to tolerate substantially high levels of CPT in their body tissue is under investigation.

Micro‐PIXE studies of Ni‐elimination strategies in representatives of two families of beetles feeding on Ni‐hyperaccumulating plant Berkheya coddii

AbstractPlants may use the ability to hyperaccumulate toxic metals in their defence against herbivores. Insects can counteract and feed on toxic plants. Among grazers of Ni‐hyperaccumulating Berkheya coddii, some beetles tolerate Ni (Chrysolina clathrata, former name Chrysolina pardalina; Epilachna nylanderi). The adaptive mechanisms against Ni toxicity were studied in these species using micro‐PIXE quantitative elemental mapping and by microscopy techniques. Distinct differences were found in mechanisms used for Ni‐elimination in both species. Functional comparisons and quantification of data extracted from selected micro‐areas in target organs responsible for metal circulation (digestive tract and Malpighian tubules) were made. Similar detoxification mechanism is used against metals through spheric granules, which in E. nylanderi are formed mainly in the midgut, while in C. clathrata in Malpighian tubules and midgut. Elemental maps showed positive correlations of Ni and Zn in Malpighian tubules of E. nylanderi without such effect in C. clathrata. Quantitative relations of K+ and Cl− indicate higher osmotic pressure increasing reabsorption of water necessary for Ni transportation to the intestine lumen and further rejection outside the body. Copyright © 2011 John Wiley & Sons, Ltd.

Impact of Cry3Bb1‐expressing Bt maize on adults of the western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Genetically engineered maize producing insecticidal Cry3Bb1 protein from Bacillus thuringiensis (Bt) is protected from root damage by corn rootworm larvae. An examination was made to establish whether western corn rootworm (Diabrotica virgifera virgifera) adults are affected by Cry3Bb1-expressing maize (MON88017) when feeding on above-ground tissue. In laboratory bioassays, adult D. v. virgifera were fed for 7 weeks with silk, leaves or pollen from Bt maize or the corresponding near-isoline. Male, but not female, survival was reduced in the Bt-leaf treatment compared with the control. Female weight was lower when fed Bt maize, and egg production was reduced in the Bt-silk treatment. ELISA measurements demonstrated that beetles feeding on silk were exposed to higher Cry3Bb1 concentrations than beetles collected from Bt-maize fields in the United States. In contrast to silk and pollen, feeding on leaves resulted in high mortality and low fecundity. Females feeding on pollen produced more eggs than on silk. C:N ratios indicated that silk does not provide enough nitrogen for optimal egg production. Direct effects of Cry3Bb1 on adult beetles could explain the observed effects, but varietal differences between Bt and control maize are also possible. The impact of Bt maize on adult populations, however, is likely to be limited.

Eavesdropping on Plant Volatiles by a Specialist Moth: Significance of Ratio and Concentration

We investigated the role that the ratio and concentration of ubiquitous plant volatiles play in providing host specificity for the diet specialist grape berry moth Paralobesia viteana (Clemens) in the process of locating its primary host plant Vitis sp. In the first flight tunnel experiment, using a previously identified attractive blend with seven common but essential components (“optimized blend”), we found that doubling the amount of six compounds singly [(E)- & (Z)-linalool oxides, nonanal, decanal, β-caryophyllene, or germacrene-D], while keeping the concentration of other compounds constant, significantly reduced female attraction (average 76% full and 59% partial upwind flight reduction) to the synthetic blends. However, doubling (E)-4,8-dimethyl 1,3,7-nonatriene had no effect on female response. In the second experiment, we manipulated the volatile profile more naturally by exposing clonal grapevines to Japanese beetle feeding. In the flight tunnel, foliar damage significantly reduced female landing on grape shoots by 72% and full upwind flight by 24%. The reduction was associated with two changes: (1) more than a two-fold increase in total amount of the seven essential volatile compounds, and (2) changes in their relative ratios. Compared to the optimized blend, synthetic blends mimicking the volatile ratio emitted by damaged grapevines resulted in an average of 87% and 32% reduction in full and partial upwind orientation, respectively, and the level of reduction was similar at both high and low doses. Taken together, these results demonstrate that the specificity of a ubiquitous volatile blend is determined, in part, by the ratio of key volatile compounds for this diet specialist. However, P. viteana was also able to accommodate significant variation in the ratio of some compounds as well as the concentration of the overall mixture. Such plasticity may be critical for phytophagous insects to successfully eavesdrop on variable host plant volatile signals.

LABORATORY ASSESSMENT OF ENTOMOPATHOGENIC FUNGI Beauveria bassiana (Balsamo) TO CONTROL THE LESSER GRAIN BORER Rhyzopertha dominica (F.) ON WHEAT KERNELS.

Effect of Beauveria bassiana on Rhyzoperthadominica parental adult mortality, F1 emerged adults, wheat kernels weight loss and damage were evaluated.Lesser grain borer,R. dominica adults were exposed to B. bassiana (BIOVER®) conidia powder admixed with wheat kernels in different six rates w/w (weight of B. bassiana conidial powder to weight of wheat kernels) and compared to untreated (check). Mortality percentage of R. dominica adults increased with increasing rates of B. bassiana after seven days. Significant differences were observed between all tested B. bassiana rates (P=0.0001). The maximum percentage of adult mortality after seven days of exposure was achieved at the highest rate compared to the untreated. Same trend was recorded after 14 days of exposure (P= 0.0001) at the previously mentioned rates compared to the untreated check. Negative relationship between B. bassiana rate and number of emerged R. dominica adults was recorded. Significant difference (P= 0.0001) was recorded between the untreated and the treated mean numbers of adult progeny emerged. The maximum adult progeny emerged was observed in the lowest rate (0.1% w/w) averaged 100.33 adult, while the minimum adult progeny emerged was recorded in the highest rate (1.0% w/w) averaged 16 adult compare to the untreated (225.33 adult). Weight loss means varied significantly among the tested rates of B. bassiana. Increasing B. bassiana rates led to significant decrease in weight loss on wheat treated. The minimum percentage of weight loss was recorded in the highest rate (1.0% w/w) compared to the untreated wheat which showed more feeding activities of the R. dominica beetles. In addition, the untreated wheat grains infested with R. dominica was significantly more damaged by the feeding of beetles than grains treated with B. bassiana. Generally, B. bassiana treated wheat kernels significantly decrease in mean numbers of F1 emerged adult, weight loss and damage compared to untreated wheat kernels. As an alternative control method of stored product insect pests, B. bassiana could be implicated as a part of integrated pest management (IPM) strategies.

Massive occurrence of Podagrica fuscicornis (L.) (Coleoptera, Chrysomelidae) on common marshmallow (Althaea officinalis L.)

In May 2011 we noticed high number of Podagrica fuscicornis adults on the leaves of common marshmallow (Althaea officinalis) grown on Laboratory Field of Biotechnical Faculty in Ljubljana. In Slovenia, this beetle was already recorded earlier but it did not caused any damage on common marshmallow (Althaea officinalis). Due to the feeding of beetles on leaves, 1 to 2 mm large holes appear. By expecting climate changes, already known bionomics of some related species and giving more emphasis on herb production in the future, Chrysomelid P. fuscicornis might represent medium sized biological factor in producing common marshmallow.

The Role of Volatile Organic Compounds in the Indirect Defense of Plants Against Insect Herbivores Above- and Belowground

Plants respond to attacks by herbivorous insects by releasing specific blends of volatile organic compounds (VOCs). These herbivore-induced VOCs are known to play a major role in the interaction between plants and insects and may directly protect the plant by being toxic or deterrent, but may also benefit the plant indirectly by attracting natural enemies of the herbivores. The chemical composition of herbivore-induced VOC blends is known for many plant–herbivore systems. Some VOCs are taxon-specific, whereas other VOCs appear to be common to many different plant families. These common compounds mainly include ‘green leaf volatiles’ (C6 aldehydes, alcohols and derivatives), cyclic and acyclic terpenes, phenolic compounds and nitrogenous compounds. Our model plant is maize, which shows a rapid reaction to an attack by caterpillars and root feeding beetle larvae. Belowground, maize roots respond within hours to feeding of larvae by releasing the sesquiterpene (E)-beta-caryophyllene. The emission of this compound results in increased recruitment of entomopathogenic nematodes (tiny worms that parasitize and kill insect larvae). Similarly, after being attacked by caterpillars aboveground, maize leaves emit a complex blend of volatiles that is attractive to parasitic wasps, which use the volatiles to find and kill the caterpillars. It remains largely unclear which VOCs within the blend are the key compounds mediating this parasitoid attraction. To study the importance of individual volatiles we combine different methods to generate and modify herbivore-induced VOC blends by manipulating the plant genotype, the plant phenotype and the headspace of volatiles produced by the plant. We focus on ‘subtractive’ approaches used to obtain blends differing in only few known VOCs and ‘additive’ approaches to generate blends of known composition. All blends are analyzed with gas chromatography/mass spectrometry and tested for attraction to the wasps in olfactometer studies. By combining the above approaches, we aim to provide new insights into the relevance of individual VOCs involved in indirect defenses, which might help to develop ecologically sound methods to control pest insects.

Prey choice by carabid beetles feeding on an earthworm community analysed using species- and lineage-specific PCR primers

The carabid beetle Pterostichus melanarius is a major natural enemy of pests, such as aphids and slugs in agricultural systems. Earthworms are a dominant non-pest component of the diet of P. melanarius which help sustain the beetles during periods when the pest population is low or absent. In this study we wanted to test whether this predator exercises prey choice among different earthworm species or ecological groups. High levels of genetic diversity within morphological species of earthworm necessitated the development of primers that were specific not just to species but lineages and sub-lineages within species as well. Gut samples from beetles were analysed using multiplex-PCR and fluorescent-labelled primers. Calibratory feeding trials were undertaken to calculate median detection times for prey DNA following ingestion. Extensive testing demonstrated that the primers were species-specific, that detection periods were negatively related to amplicon size and that meal size had a highly significant effect on detection periods. Monte Carlo simulations showed that, in general, worms were being predated in proportion to their densities in the field with little evidence of prey choice, other than probable avoidance of the larger, deep-living species. There was no evidence that epigeic species were being taken preferentially in comparison with endogeic species. There was also no evidence that defensive secretions by Allolobophora chlorotica reduced predation pressure on this species by P. melanarius. We concluded that any management system that increases earthworm densities generally, regardless of component species, is likely to be optimal for increasing numbers of this beneficial beetle predator.

Density-dependent processes in leaf beetles feeding on purple loosestrife: aggregative behaviour affecting individual growth rates

Aggregative responses are commonly observed in insects, including chrysomelids, affecting both individual and population growth rates. In two closely related chrysomelid beetles (Galerucella calmariensis and G. pusilla) feeding on purple loosestrife (Lythrum salicaria), recent studies suggest that male-produced pheromones may cause both inter- and intraspecific attraction. This paper further examines the causes and consequences of feeding aggregations in these species. Olfactometer studies confirm previous findings, showing cross-species attraction to damaged plants, but suggest that also damaged induced plant volatiles may be involved. In addition, the studies suggest that the cross-species attraction observed in previous studies have asymmetric effects on the two beetles. Galerucella pusilla was more attracted to damage by G. calmariensis than to damage by conspecifics. Laboratory and field data suggest that feeding aggregations in these species increase pupal mass, at least at low to intermediate larval densities. This positive feedback may have important consequences for the spatiotemporal dynamics and as a consequence on the role of the two chrysomelid beetles on biological control of purple loosestrife.