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Bareogonalos xibeidai Tan and van Achterberg, 2017 (Hymenoptera: Trigonalyidae) was newly recognized in South Korea. The species was reared from the nest cells of the Korean yellowjacket, Vespula koreensis koreensis Radoszkowski, 1887 (Hymenoptera: Vespidae), which is a new host record for the trigonalid species. Diagnoses and images of the species and genus are provided in the present study.

Inbreeding can have negative consequences on population viability because of the reduced fitness of the progeny. In general, most species have developed mechanisms to minimize inbreeding such as dispersal and kin avoidance behavior. In the eusocial Hymenoptera, related individuals typically share a common nest and have relatively short mating periods, this could lead to inbreeding, and because of their single?locus complementary sex determination system, it may generate diploid males that could result in infertile triploid progeny representing a cost for the colony. Vespula germanica, is an eusocial wasp that has invaded many parts of the world, despite likely facing a reduced genetic pool during the arrival phases. We ask whether male wasp display specific aggregation behavior that favors genetic diversity, key to reduce inbreeding. Through a set of laboratory experiments, we investigated the effects of drone nestmateship and density on the aggregation behavior of V. germanica drones. We show that drones avoid aggregating with their nestmates at all densities while non-nestmates are avoided only at high densities. This suggests that lek genetic diversity and density could be regulated through drone behavior and in the long run minimize inbreeding favoring invasion success. Fil: Masciocchi, Maité. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina Fil: Angeletti, Bárbara. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina Fil: Corley, Juan Carlos. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina Fil: Martinez Von Ellrichshausen, Andres Santiago. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina

In geographic regions with warm winters, invasive yellowjacket wasp colonies (genus Vespula) often exhibit polygyny (multiple queens) and persist for multiple years, despite these phenomena being rare in the native range. Here, we test the hypothesis that polygyny, caused by foreign queens being accepted into an existing colony, is the result of relaxed nestmate recognition in the invasive range, as has been observed in some supercolonial invasive ants. In bioassays with wild colonies in the field, we found that nestmate discrimination was weak in both invasive (Hawaii) and native (California) populations of Vespula pensylvanica, with significant nestmate discrimination in only ~ 30% of trials. We also found that the diversity and variability of cuticular hydrocarbons, chemical compounds that mediate nestmate recognition, were not reduced in introduced populations, unlike several supercolonial invasive ant species. Our findings suggest that ancestral weak nestmate discrimination behavior of V. pensylvanica may make this species pre-adapted to transition to polygyny and extended colony lifespans when introduced into environments with benign winters that facilitate foreign queens joining existing colonies in late season.

Baiting is an effective method to manage Vespula spp. yellowjacket (Hymenoptera: Vespidae) populations without having to locate and treat nests. Here, we assessed the utility of a commercially available polyacrylamide hydrogel as an alternative bait material for yellowjacket baiting. The experimental bait (hereafter referred to as 'hydrogel bait') consisted of diluted chicken juice (from canned chicken meat) and fipronil (0.025%, wt/wt) absorbed into granular polyacrylamide hydrogel particles. Three separate 24-h baiting trials were conducted at two different field sites with the western yellowjacket, Vespula pensylvanica (Saussare), as the target species. The monitoring data from pre- and posttreatment periods indicated that baiting with polyacrylamide hydrogel baits provided ≈74-96% reduction in the foraging activity of V. pensylvanica during its active season. In addition to their ability to absorb large quantities of aqueous bait containing phagostimulants and toxicants, the hydrogels' tactile resemblance to fresh meat upon hydration makes them a promising option as a non-meat material for delivering small amounts of insecticides to yellowjacket populations in a highly targeted manner.

Little is known about the roles of sex pheromones in mate-finding behavior of social wasps (Vespidae). Working with the aerial yellowjacket, Dolichovespula arenaria (Fabricius), baldfaced hornet, Dolichovespula maculata (L.), western yellowjacket, Vespula pensylvanica (Saussure), southern yellowjacket, Vespula squamosa (Drury), and Vespula alascensisPackard, we tested the hypotheses (1) that gynes produce an airborne sex pheromone attractive to males, and (2) that males are more strongly attracted to non-sibling gynes based on olfactory cues. A field experiment provided the first definitive evidence that D. arenaria gynes attract males. Surprisingly, we did not find such evidence in similar field experiments for sexual attractiveness of gynes of V. squamosa, V. pensylvanica, V. alascensis, or D. maculata. In Y-tube olfactometer experiments with three of these species (D. arenaria, D. maculata, V. pensylvanica), only D. maculata gynes attracted males, provided they were non-siblings, implying an olfactory-based mechanism of nestmate recognition and inbreeding avoidance. Lack of sex attraction responses for V. pensylvanica, V. alascensis, and V. squamosa in this study does not rule out pheromone-mediated sexual communication. Instead, it highlights the possibility that pheromonal signaling may be dependent on the presence of appropriate contextual cues.

The yellowjacket, Vespula squamosa (Drury) (Hymenoptera: Vespidae), is the only eusocial wasp that commonly has 2 social forms (monogyne and polygyne nests), has annual and perennial nests, facultatively usurps the nests of conspecifics, and parasitizes other vespine species. Thus, V. squamosa is ideally suited for examining various phenotypic and genetic variables as they relate to different social alternatives in the context of kin selection theory. In this study, we compared various metrics relating to reproduction for queens in monogyne versus polygyne nests including queen abdominal weight, fertility, egg number, egg size, and worker relatedness. Monogyne nests (N = 7) and polygyne nests (N = 5) were collected from Georgia and Florida, USA. Examination of nest comb material indicated all polygyne nests were perennial; the number of workers in these nests varied from approximately 700 to 36,379. All monogyne nests were annual and had fewer than 1,500 workers. Single queens were more physogastric than their polygyne counterparts and had significantly more mature eggs per ovary. Polygyne queens, however, had significantly larger eggs but produced smaller workers. Twelve percent of the queens in polygyne nests were either devoid of sperm or did not have full spermathecae (n = 142), whereas the spermathecae of single queens (n = 7) were replete with spermatozoa. Mean genetic relatedness among workers in perennial, polygyne nests suggests these nests include multiple egg-laying queens.

Eusociality, a form of animal social organization involving sterile and reproductive castes, is a rare, but highly ecologically successful form of life. There are striking examples of eusocial species with populations that are ecologically dominant in their native ranges, as well as remarkably successful globally as invasive species; prominent examples include fire ants and yellowjacket wasps. At the same time, there have been startling population declines in other social insects, notably bumble bees. Here, we explore the possible role of phenotypic plasticity in invasion biology and declines of social insect species. This topic is of particular interest, because social insects exhibit extreme behavioral, developmental, physiological, and morphological plasticity. It has been suggested that this plasticity may contribute to ecological dominance in some species, but could be a liability or cost to others. In this review, we explore the relationship between phenotypic plasticity, invasion biology, and vulnerability to global change in social insects. By considering plasticity at three levels–molecular, individual, and colony—we suggest ways in which considerations of phenotypic plasticity may help in managing social insect populations. Fil: Manfredini, Fabio. University of London; Reino Unido. University of Aberdeen; Reino Unido Fil: Arbetman, Marina Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina Fil: Toth, Amy L.. Iowa State University; Estados Unidos

This paper estimates the ecosystem services return on investment in government control of the introduced European wasp (Vespula germanica) in the state of Western Australia. The predictive model used accounts for uncertainties in the spread and impact ofV. germanicaon provisioning ecosystem services, represented by pollination, apiculture and viticulture, and cultural ecosystem services represented by households. Results produced by simulating a 20-year period suggest government expenditure on management will generate net benefits of AU$3.2–6.3 million per year, most of which will accrue to producers of pollination-dependent crops. This provides justification for investment from the government’s agriculture portfolio to manage an insect often thought of as an urban pest.

Understanding the factors that affect animal dispersal behavior is important from both fundamental and applied perspectives. Dispersal can have clear evolutionary and ecological consequences, but for nonnative insect pests, dispersal capacity can also help to explain invasion success. Vespula germanica is a social wasp that, in the last century, has successfully invaded several regions of the world, showing one of the highest spread rates reported for a nonnative insect. In contrast with nonsocial wasps, in social species, queens are responsible for population redistribution and spread, as workers are sterile. For V. germanica, it has been observed that queen flight is limited to 2 distinct periods: early autumn, when new queens leave the nest to mate and find sheltered places in which to hibernate, and spring when new colonies are founded. Our aim was to study the flight behavior of V. germanica queens by focusing on the different periods in which dispersal occurs, characterizing as well the potential contribution of queen flight (i.e., distance) to the observed geographical spread. Our results suggest that the distances flown by nonoverwintered queens is greater than that flown by overwintered individuals, suggesting that the main queen dispersal events would occur before queens enter hibernation. This could relate to a behavioral trait of the queens to avoid the inbreeding with related drones. Additionally, given the short distances flown and remarkable geographical spread observed, we provide evidence showing that queen dispersal by flight is likely to contribute proportionately less to population spread than human-aided factors.

Previously, we showed that the symbiotic yeast Lachancea thermotolerans (Filippov) (Saccharomycetales: Saccharomycetaceae) is attractive to its Vespula (Hymenoptera: Vespidae) yellowjacket hosts when grown on media supplemented with grape juice. We hypothesized that "Concerto", a commercial strain of this yeast, could be combined with fruit powder to form a shelf-stable bait for trapping yellowjackets. Using molecular techniques, we first confirmed that Concerto yeast is indeed the species L. thermotolerans. We then tested whether: 1) Concerto yeast produces volatiles similar to those produced by L. thermotolerans isolated from yellowjackets, 2) Concerto yeast enhances attraction of yellowjackets to fruit powder, 3) a Concerto yeast/fruit powder bait interacts synergistically with a yellowjacket semiochemical lure, and 4) a synthetic analog blend of Concerto-produced volatiles attracts yellowjackets. Using gas chromatography-mass spectrometry, we demonstrated that the chemical composition of Concerto-produced volatiles closely resembles that produced by a yellowjacket-isolated strain of L. thermotolerans. In field experiments, addition of Concerto to fruit powder doubled its attractiveness to yellowjackets. Addition of the Concerto/fruit powder bait to a heptyl butyrate-based wasp lure revealed a weak additive effect. A three-component synthetic analog blend of volatiles identified from the Concerto/fruit powder bait attracted Vespula pensylvanica (Saussure), but no other yellowjacket species. Our results suggest that commercial L. thermotolerans in combination with fruit powder could be used as a yellowjacket bait, and that addition of yeast-produced volatiles to a commercial wasp lure may improve its attractiveness to V. pensylvanica. Further research should determine why the synthetic volatile blend failed to attract Vespula species other than V. pensylvanica.

The German yellowjacket (Vespula germanica) is an opportunist predator and a scavenger, whose eclectic diet also includes honey, brood, dead and live honey-bees. There is no evidence in this species of coordinated attacks against bees involving other conspecifics, although intraspecific competition has been already reported between two or more individuals during feeding. Our aim was to gain further knowledge on the feeding behavior of V. germanica in order to evaluate its role in an apiary. Sight observations of predation and necrophagy behaviors were carried out at the ground level near hives. We also investigated how intraspecific competition can influence the feeding display in this species. Our results confirm the major role of the German yellowjacket as a scavenger, because its diet is based mostly on bee carrions. Intraspecific competition during feeding was sometimes observed. When these events occurred, the interference of another wasp led to the bee escaping only in three cases. Our study also revealed that intraspecific competition events increase when the resource is fresh (predation vs necrophagy), and that the number of competing wasps was significantly higher when the food consisted of pupae and drones, compared to adult bees. When competition involved two individuals (the most frequent case), the winner was frequently the first wasp to reach the resource in both predation and necrophagy events. This suggests that the energy invested in foraging or predating activity and in defence of prey is usually rewarded.

The Hymenoptera is one of the vital and biggest insect orders comprising the bees, wasps, sawflies, and ants. Wasps are important to natural and biological pest control because they are predators or parasitoids of pest arthropods. This study investigated the genetic diversity among the three wasps, Vespa orientalis Linnaeus, Polistes bucharensis Erichson, and Polistes mongolicus du Buysson, collected from three different governorates in Egypt, using cytochrome oxidase subunit I (COI) DNA barcoding. PCR was performed to amplify COI fragment. The amplified COI regions (710 bp) were sequenced and analyzed. All novel nucleotide sequences of COI gene were deposited into the GenBank database. The genetic distances were estimated using Kimura two-parameter model. In spite of the wide geographical range, minor genetic diversity was observed between some populations of the three wasp species, revealing unrestricted gene flow between them. Phylogenetic relationship analysis was performed, using maximum likelihood (ML) method. The results of the phylogenetic analyses recovered P. bucharensis more closely related to P. dominula and P. gallicus. P. mongolicus collected from Menofia Governorate formed a distinct branch with 99% support. V. orientalis was sister to the yellowjacket Dolichovespula adulterine, with 84% support. It can be concluded that DNA barcode is a powerful tool for rapid and accurate identification of Egyptian wasp species.

Several yellowjacket species are important pests in both their native habitat and in areas where they are invasive. Traps that contain one or more chemical attractants to lure insects inside are commonly used to combat these yellowjackets in urban environments. Usually, attractants are placed within the trap and combined indiscriminately, though little is known about how this design influences trap attractiveness or efficacy. Here, using the common attractant heptyl butyrate in combination with chicken extract, we demonstrate that spatial partitioning of attractants results in increased capture of the western yellowjacket Vespula pensylvanica—a widespread pestiferous species. Specifically, we show that partitioning of these attractants results in increased visitation of yellowjackets to a trap while also leading to more individuals entering the trap. Further, we provide evidence that this effect is driven by the ability of heptyl butyrate to function as an attractant to the general location of the trap while also blocking the effects of meat extract as a trap-entering stimulus. Thus, our data challenge the current paradigm of combining attractants inside yellowjacket traps, and suggest that these methods can be improved through the consideration of spatial variables and interactions. Our results not only provide novel insight into the mechanisms of yellowjacket attraction, but are also likely to be applicable to the control of other insects for which attractant-based traps are used.

Stings by honey bees (Apis), bumble bees (Bombus), yellowjacket wasps (Vespula and Dolichovespula), paper wasps (Polistes), hornets (Vespa), fire ants (Solenopsis), other ants (Myrmecia, Pogonomyrmex, Myrmica, Brachyponera, Wasmannia, etc.), and a variety of tropical social wasps (Polybia, etc.) constitute an important medical challenge for clinicians and a physical and psychological challenge for patients. The behavior and biology of the major stinging insects responsible for causing hypersensitive reactions is presented with emphasis on how providers can educate their patients to prevent future stings and the disabling fear these insects sometimes engender.

Social insects often serve as model systems for communication and recruitment studies, and yet, it remains controversial whether social vespid wasps can reliably communicate resource information to nestmates. In this study, I present empirical evidence that foraging strategies depend on the initial assessment of resource size and potential competition by foraging yellowjackets. The context dependent foraging behavior of Vespula pensylvanica provides a potential explanation for the inconsistent reports of the existence of recruitment communication in vespid wasps. Furthermore, life history traits may influence yellowjacket foraging behavior; annual V. pensylvanica colonies, whose foragers routinely patrol near the nest, exhibited increased bait visitation in response to the return of successful foragers, whereas perennial colonies did not. These behavioral disparities provide insight into how foraging strategies and search patterns may shift with colony size and longevity. In experiments that investigate the effects of visual cues of conspecifics and bait dispersion, foraging decisions corresponded with expectations of yellowjackets integrating resource quantity and access into a perception of demand. When resource competition could be assessed as high, V. pensylvanica foragers quickly exploited the bait closest to their colony regardless of occupation by other wasps; however, foragers preferred visiting unoccupied baits in situations where competition could be perceived as low. Moreover, a meta-analysis revealed that context-dependent, cue-mediated recruitment was widespread in Vespidae, where such foraging behaviors changed with habitat and the potential for resource competition. Such plastic foraging strategies may contribute to the invasion success of some vespid wasps.

In many colonies of social insects, the workers compete with each other and with the queen over the production of the colony's males. In some species of social bees and wasps with annual societies, this intra-colony conflict even results in matricide-the killing of the colony's irreplaceable queen by a daughter worker. In colonies with low effective paternity and high worker-worker relatedness, workers value worker-laid males more than queen-laid males, and thus may benefit from queen killing. Workers gain by eliminating the queen because she is a competing source of male eggs and actively inhibits worker reproduction through policing. However, matricide may be costly to workers if it reduces the production of valuable new queens and workers. Here, I test a theoretical prediction regarding the timing of matricide in a wasp, Dolichovespula arenaria, recently shown to have facultative matricide based on intra-colony relatedness. Using analyses of collected, mature colonies and a surgical manipulation preventing queens from laying female eggs, I show that workers do not preferentially kill queens who are only producing male eggs. Instead, workers sometimes kill queens laying valuable females, suggesting a high cost of matricide. Although matricide is common and typically occurs only in low-paternity colonies, it seems that workers sometimes pay substantial costs in this expression of conflict over male parentage.

In social insects, selection takes place primarily at the level of the colony. Therefore, unlike solitary insects, social species are expected to forage at rates that maximize colony fitness rather than individual fitness. Workers can increase the net benefit of foraging by responding to increased resource availability, by responding more strongly to higher-quality resources, and by decreasing the uncertainty with which nestmates find resources. Unlike many ants and social bees, no social wasp is known to utilize a nest-based recruitment signal to inform nestmates of food location. On the other hand, wasps do learn the odor of food brought to the nest and use this cue to locate the food source outside the nest. Here, we quantify the effects of three food-associated variables on the allocation of foraging effort in the yellowjacket Vespula germanica. We used an experimental approach to assess whether resource quantity, quality, or associated olfactory information affect the probability that a forager will leave the nest on a foraging trip. We addressed these questions by inserting a known amount of sucrose solution directly into nests and recording foraging effort (departure rate) over the subsequent hour-long observation period. No differences were found in foraging effort because of the presence/absence of olfactory cues, but there was strong evidence that foraging effort increased in response to resource influx and resource quality. Thus, while olfactory cues are learned in the nest, only resource quality and the cue of increased amount of food in the nest factor into a forager's decision of whether or not to depart on a foraging trip. However, as prior work has shown, once a wasp forager leaves the nest, it uses the learned olfactory cues to aid in finding resources.

BACKGROUND: The invasive western yellowjacket wasp, Vespula pensylvanica (Saussure), has significantly impacted the ecological integrity and human welfare of Hawaii. The goals of the present study were (1) to evaluate the immediate and long-term efficacy of a 0.1% fipronil chicken bait on V. pensylvanica populations in Hawaii Volcanoes National Park, (2) to quantify gains in efficacy using the attractant heptyl butyrate in the bait stations and (3) to measure the benefits of this approach for minimizing non-target impacts to other arthropods. RESULTS: The 0.1% fipronil chicken bait reduced the abundance of V. pensylvanica by 95 ± 1.2% during the 3 months following treatment and maintained a population reduction of 60.9 ± 3.1% a year after treatment in the fipronil-treated sites when compared with chicken-only sites. The addition of heptyl butyrate to the bait stations significantly increased V. pensylvanica forager visitation and bait take and significantly reduced the non-target impacts of fipronil baiting. CONCLUSION: In this study, 0.1% fipronil chicken bait with the addition of heptyl butyrate was found to be an extremely effective large-scale management strategy and provided the first evidence of a wasp suppression program impacting Vepsula populations a year after treatment. Copyright © 2011 Society of Chemical Industry

Nutritional variation among developing larvae is a long-standing hypothesis for how a sterile caste could evolve, with larvae deprived of nutrition becoming sterile or not leaving the nest. In this study, we test whether the three castes of the eusocial yellowjacket wasp (Vespula maculifrons) differ in the trophic source of their larval diet, their overall carbon (C) and nitrogen (N) content, as well as the distribution of C and N across body parts. Virgin queens (gynes) assimilated food from a higher relative trophic level compared to males, and workers were the lowest. Gynes, due to their much greater mass compared to the other castes are much more costly in terms of N, but males have the lowest C:N ratio. The variation in C:N is likely due to differences in life history between males and females (gynes and workers), where females invest more in energy storage (e.g., lipids) compared to males which have very short life spans; the major difference is in the abdomen, where fat is stored. The results of this study complement similar results in ants, which evolved a reproductive division of labor independently, and which diverged from vespid wasps near 150 million years ago. Similarities between how wasp and ant caste determination occurs suggest either a conserved mechanism that predates the evolution of eusociality or convergence on the same mechanism for generating alternative phenotypes. Provisioning N-expensive castes with food from a higher trophic level likely increases efficiency of N delivery because of N-enrichment with increasing trophic level.

We examined the foraging behavior of the Korean yellowjacket, Vespula koreensis, to determine whether this species displays temporal polyethism. Using video-recordings of the entrances of artificial nest boxes installed in the field, we investigated the association between the tasks performed by workers and age. We identified three foraging tasks (pulp, nectar and prey foraging). Pulp foraging was performed by younger foragers, while nectar and prey foraging were performed by older foragers. We measured the foraging time (time spent outside of the nest during a single foraging bout) and the weight of the materials that foragers brought into the nest for each task to estimate the cost of the task. Pulp foraging was less costly than nectar or prey foraging by both measures. Taken together, the results suggest that yellowjacket foragers tend to perform low-cost task in their early foraging days and high-cost task later. Our results add to a growing literature showing temporal polyethism in social insects.

The classic formulation of optimal foraging theory predicts that a central-place forager will gather more food if it is required to travel farther from the nest to find that food. We examined the foraging behavior of German yellowjackets (Vespula germanica) to determine whether carbohydrate foragers follow this pattern. We trained foragers to collect 2 M fructose solution at 5 or 50 m from the nest and measured the time spent feeding, load size, and the rate of delivery. We show that as a forager’s crop fills during a foraging bout, the amount of solution ingested per second decreased. However, load size did not change as wasps collected food up to 50 m from the nest. Instead, temperature and body size were better predictors of the volume of fructose a forager carried. Finally, the rate of fructose delivered to the nest was higher at warmer temperatures. Due to the fact that wasps gather more food but feed for shorter periods of time at warmer temperatures, we found an overall negative relationship between feeding time and load size. We conclude that the strong effects temperature had on the behavior of V. germanica foragers imply that feeding time may not always be an accurate predictor of the size of the load an individual carries back to the nest. Results from this study suggest that in yellowjacket colonies, foragers can collect and bring disproportionately more food back to the nest during the warmest days of the summer, a time of year when this pest species reaches peak population size during its annual colony cycle.

The German yellowjacket, Vespula germanica (F.) (Hymenoptera: Vespidae), is a highly invasive wasp that exhibits efficient mechanisms while foraging. Plastic cognitive systems might be advantageous for invasive species given that they repeatedly encounter dynamic, unknown, or unpredictable environments. In this study, we explore memory dynamics of wasp foragers dealing with changing contexts. The aim of this work was to analyze how learning a second task interferes with the retrieval of a first learned task. We demonstrate that V. germanica wasps integrate old and new memories while foraging on nondepleted food sources. Learning a second task interferes with a first learned task when both tasks have different response requirements, probably due to response competition. Memories associated with the first learned task are not wiped out. Interestingly, this pattern of memory interference does not change when decreasing the number of feeding trials. This study provides new evidence about the complex cognitive mechanisms of V. germanica wasps, which integrate old and new experiences after very few learning episodes. To our knowledge, this is the first study on memory interference in social wasps.

Southern yellowjackets, Vespula squamosa (Drury) were collected at sites in Guatemala, in the Departments of Baja Verapaz, El Progresso, and Zacapa. Collection localities ranged in elevation from 500 to 1,880 m. These locations were forested, or partially forested with some pasture land and coffee plantings, Coffea arabica L. Two active colonies of this wasp were collected and analyzed in May of 2006. The two colonies were subterranean, and the nests had 9 and 11 layers, respectively, of paper comb completely surrounded with external paper envelope. The two nests included 10,581 and 20,715 cells, with 2,818 and 6,105 workers, 203 and 313 queens, and 790 and 454 males respectively. Samples of queens from each nest were dissected. These included numerous queens that were mated and possessed mature eggs, as well as numbers of queens that were unmated and had no eggs. Workers from each nest showed no ovarian development. The nest sizes and populations of wasps for these colonies were within ranges of those reported for nests of this species in North America.

Social insects can modulate body temperature to increase foraging efficiency; however, little is known about how the relative value of protein resources affects forager body temperature. Such regulation may be important given that colony growth is often limited by protein availability. In this paper, we present what are, to our knowledge, the first data for social insects showing that thoracic temperatures (T (th)) of foragers increase with the protein content of food resources. In an introduced population of western yellowjacket (Vespula pensylvanica), we measured T (th) of foragers collecting high-quality protein (100% canned chicken) and low-quality protein (50% canned chicken, 50% indigestible alpha-cellulose by volume) at different ambient air temperatures (T (a)). Wasps foraging on 100% chicken consistently exhibited higher T (th) compared to wasps foraging on 50% chicken. After correcting for T (a), the mean T (th) for wasps collecting 100% chicken were 1.98 degrees C higher than those of individuals collecting 50% chicken. We suggest that this mechanism may increase foraging efficiency in this and other social wasp species.

We investigated field-based recruitment via visual, chemical and acoustic cues provided by conspecific wasps on carbohydrate feeders in Vespula koreensis. A wild colony nest was excavated and artificially installed in a field site. Naive foragers were individually marked and trained to an experimental feeder. We conducted three separate experiments in which foragers were presented with feeder dishes with different cue intensities. For the first, a different number of decoys were posed as if feeding (visual cue). In the second, dishes had been previously visited by different numbers of individuals, thus presenting different concentrations of a possible food site marking substance (chemical cue). In the third, each dish was placed in front of a covered flask with a different number of nestmates inside (acoustic cue combined with body-odor cue). We observed no social facilitation or social inhibition due to any of the experimental cues. Previous studies in Vespula species have shown a variety of foraging strategies ranging from local enhancement to local inhibition. Field-based recruitment mechanisms in yellowjackets may have evolved independently in different lineages.

The wing venation is frequently used as a morphological marker to distinguish biological groups among insects. With geometric morphometrics, minute shape differences can be detected between closely related species or populations, making this technique useful for taxonomy. However, the direct influence of genetic differences on wing morphology has not been explored within colonies of social insects. Here, we show that the father's genotype has a direct effect on wing morphology in colonies of social wasps. Using geometric morphometrics on the venation pattern, we found significant differences in wing size and shape between patrilines of yellowjackets, taking allometry and measurement error into account. The genetic influence on wing size accounted for a small part of the overall size variation, but venation shape was highly structured by the differences between patrilines. Overall, our results showed a strong genetic influence on wing morphology likely acting at multiple levels of venation pattern development. This confirmed the pertinence of this marker for taxonomic purposes and suggests this phenotype as a potentially useful marker for phylogenies. This also raises doubts about the strength of selective pressures on this phenotype, which highlights the need to understand better the role of wing venation shape in insect flight.

The German yellowjacket, Vespula germanica (F.) (Hymenoptera: Vespidae), was introduced into Australia in 1959 and has established throughout southern Australia. In urban environments, V. germanica is frequently a nuisance pest at public gatherings and to homeowners. In native environments, it has the potential to pose a threat to native invertebrates. The current practice for controlling the wasps is nest destruction with pesticide. However, locating the nest(s) is not always practical or possible. Meat baits impregnated with an insecticide that foraging wasps cut and carry back to the nest offer a means of suppressing wasps where the nest sites are unknown. The success of meat baits depends on the attractiveness and acceptance of the meat to the wasp and the mode of action of the insecticide. Our objective was to determine wasp preference and acceptance of five processed meats: canned chicken or fish and freeze-dried chicken, fish, or kangaroo. We found that more wasps visited and took freeze-dried kangaroo and canned chicken than the other baits. Canned and freeze-dried fish were similarly preferred, and freeze-dried chicken was the least attractive and accepted by foraging wasps. Our findings demonstrate that wasps prefer some processed meats and hence take more loads back to the nest. By combining a suitable insecticide with a meat bait preferred by wasps, the likelihood of effective suppression of nuisance wasp populations should be increased.

Prior work has shown that yellowjacket wasps remember food odors and use them as cues when foraging. There is also evidence they have mechanisms to recruit nest mates to highly rewarding food sources, as naive individuals are more likely to go to food sources with scents similar to those visited by nest mates. We asked whether recruitment requires behavioral stimulation by returning foragers, as in honey bees, or if sampling the food source inside the nest is sufficient. We tested this by eliminating the behavior of returning foragers by inserting a scented sugar solution directly into a Vespula germanica nest. Exiting foragers were given a choice of the test scent and a control scent. Wasps were more likely to choose the test scent. We conclude that behavioral interactions with returning foragers are not necessary to stimulate nest mates to associate an odor with a food source and search for a resource bearing that odor, and that experience with the scented reward inside the nest is sufficient to achieve this result.

Mutual policing is an important mechanism for maintaining social harmony in group-living organisms. In some ants, bees, and wasps, workers police male eggs laid by other workers in order to maintain the reproductive primacy of the queen. Kin selection theory predicts that multiple mating by the queen is one factor that can selectively favor worker policing. This is because when the queen is mated to multiple males, workers are more closely related to queen's sons than to the sons of other workers. Here we provide an additional test of worker policing theory in Vespinae wasps. We show that the yellowjacket Vespula rufa is characterized by low mating frequency, and that a significant percentage of the males are workers' sons. This supports theoretical predictions for paternities below 2, and contrasts with other Vespula species, in which paternities are higher and few or no adult males are worker produced, probably due to worker policing, which has been shown in one species, Vespula vulgaris. Behavioral observations support the hypothesis that V. rufa has much reduced worker policing compared to other Vespula. In addition, a significant proportion of worker-laid eggs were policed by the queen. ispartof: Evolution vol:59 issue:6 pages:1306-14 ispartof: location:United States status: published

Measurements of carbohydrate foraging behavior of Vespula germanica yellowjackets show that the distribution of the number of foragers over the number of trips is highly skewed with a few foragers making a disproportionate number of trips. We tested several empirical models based on different biological assumptions to see which model best described the distribution. For all periods of observation, the data are well fitted by a straight line on a log-log plot. This fit indicates that the distribution of labor is non-increasing monotonic; i.e. continually decreasing, and follows a power law. Stochasticity and self-organization are two possible explanations for the power law distribution. As an alternative approach, cluster analysis of various foraging characteristics of individual foragers clearly separated foragers into two groups and is consistent with a bimodal model for the division of foraging labor. Based on these cluster results, we operationally defined workers as either 'elite' or 'non-elite'. We found that elite foragers are not more likely than non-elites to be task specialists. The data show that workers develop into elites but do not support the hypothesis of self-reinforcement as the mechanism.

Changes in intraspecific social organization are of particular interest to sociobiologists, because an understanding of the genetic and ecological determinants of different social forms bears on the origins of sociality and mating isolation. The Southern Yellowjacket, Vespula squamosa (Drury), occurs as both polygyne and single queen nests. This study examined intra-caste size differences between both social forms of nests. Four polygyne and 13 single queen nests were collected from counties in Florida and Georgia. All single queen nests were one season old, whereas polygyne nests were at least 2 years old. The latter had significantly more workers per nest (p 0.72), whereas the lowest positive correlations were obtained between weight and all other measures of size (r < 0.64). Gynes of both social forms differed significantly in weight (p < 0.001) and thorax length (p < 0.04), whereas workers differed significantly for all six measures of size (p < 0.04 to p < 0.001).

Plant-pollinator mutualisms are disrupted by a variety of competitive interactions between introduced and native floral visitors. The invasive western yellowjacket wasp, Vespula pensylvanica, is an aggressive nectar thief of the dominant endemic Hawaiian tree species, Metrosideros polymorpha. We conducted a large-scale, multiyear manipulative experiment to investigate the impacts of V. pensylvanica on the structure and behavior of the M. polymorpha pollinator community, including competitive mechanisms related to resource availability. Our results demonstrate that V. pensylvanica, through both superior exploitative and interference competition, influences resource partitioning and displaces native and nonnative M. polymorpha pollinators. Furthermore, the restructuring of the pollinator community due to V. pensylvanica competition and predation results in a significant decrease in the overall pollinator effectiveness and fruit set of M. polymorpha. This research highlights both the competitive mechanisms and contrasting effects of social insect invaders on plant-pollinator mutualisms and the role of competition in pollinator community structure.

In annual hymenopteran societies headed by a single outbred queen, paternity (determined by queen mating frequency and sperm use) is the sole variable affecting colony kin structure and is therefore a key predictor of colony reproductive characteristics. Here we investigate paternity and male production in five species of Dolichovespula wasps. Twenty workers from each of 10 colonies of each of five species, 1000 workers in total, were analysed at three DNA microsatellite loci to estimate paternity. To examine the relationship between kin structure and reproductive behaviour, worker ovary activation was assessed by dissection and the maternal origin of adult males was assessed by DNA microsatellites. Effective paternity was low in all species (D.media 1.08, D. maculata 1.0, D. sylvestris 1.15, D. norwegica 1.08 and D. saxonica 1.35), leading to the prediction of queen?worker conflict over male production. In support of this, workers with full-size eggs in their ovaries (four out of five species) and adult males that were workers? sons (all five species) were found in queenright colonies. However, workers were only responsible for a minority of male production (D.media 7.4%, D. maculata 20.9%, D. sylvestris 9.8%, D. norwegica 2.6% and D. saxonica 34.6%) suggesting that the queen maintains considerable reproductive power over the workers. Kin structure and reproductive conflict in Dolichovespula contrast with their sister group Vespula. Dolichovespula is characterized by low paternity, worker reproduction, and queen?worker conflict and Vespula by high paternity, effective worker policing and absence of worker reproduction. The trend revealed by this comparison is as predicted by kin selection theory suggesting that colony kin structure has been pivotal in the evolution of the yellowjacket wasps.

The role of visual cues provided by resident wasps on resource choice by yellowjacket and paper wasp foragers was investigated. Large spring queen yellowjackets and small early season yellowjacket foragers (Vespula germanica, Vespula maculifrons, and Vespula vidua) were extracted in hexane to remove odors and posed as though feeding at petri dish feeders bearing daisy-like flower models, equipped with microcapillary feeding tubes, and containing 1:3 honey:water solution. An array of five feeders was presented to foragers at a suburban and a woodland site in Saratoga Springs, New York. The visual cues provided by resident wasps influenced resource choice by approaching social wasp foragers. Vespula germanica, an introduced yellowjacket species that tends to dominate at rich resources, was the only wasp visiting the suburban feeders. Foragers of this species preferentially fed on feeders and flowers with posed wasps and fed most often next to large wasps. Polistes fuscatus foragers at the woodland site similarly preferred to feed on occupied feeders and flowers. Vespula maculifrons and V. consobrina preferentially visited unoccupied feeders. Individual V. maculifrons, V. consobrina and V. vidua foragers that landed on occupied feeders all preferentially visited unoccupied flowers on those feeders. Vespula vidua and V. flavopilosa foragers did not demonstrate a feeder preference based on the presence/absence of posed wasps. Vespula consobrina foragers that visited occupied feeders preferred those occupied by extracted V. maculifrons queens and workers; no other wasps showed species based landing preferences.

Sphecophaga vesparum vesparum (Curtis) has been released in New Zealand as a biological control agent for the introduced yellowjackets Vespula vulgaris (L.) and V. germanica (F.). The parasitoid has an overwintering cocoon stage that can remain in the subterranean nest cavity for 1–4 yr before emerging. A mathematical model of the potential effect of the parasitoid has suggested that the probability of survival of overwintering cocoons and the pattern of cocoon emergence are 2 key variables for predicting the ultimate suppression in yellowjacket abundance. Overwintering cocoons were buried in subterranean cavities to simulate natural conditions and rates of cocoon predation by rodents, plus mortality from other causes, and emergence patterns were recorded. Rodents killed 62% of cocoons over 3 yr, and flooding, insects, and unknown causes of mortality accounted for another 19.2%. The mean annual survival rate for overwintering cocoons was 0.56, considerably higher than the model predicted. Emergence of adults was delayed in comparison with above-ground parasitoid release boxes, with the majority of subterranean cocoons remaining dormant until their 3rd spring. Using the higher survival rate and delayed emergence pattern in the model for the effect of the parasitoid suggests that the maximum likely reduction of yellowjacket density may be greater than originally predicted but will take longer to achieve. However, data on the proportion of spring nests killed by the parasitoid is needed before the model can usefully predict the ultimate level of suppression of yellowjacket density.

In a previous field study we demonstrated that predation on pheromone calling Mediterranean fruit fly, Ceratitis capitata (Wiedemann), males by the yellowjacket wasps Vespula gennanica (F.) is mediated through olfactory foraging behavior. The objectives of the current study were to assess wasp predation on sexually immature and mature C. capitata engaged in sexual and nonsexual activites on foliage and fruit and to confirm whether overall wasp attacks and prey capture rates are sexually biased. Our results indicate that capture rate of flies by foraging wasps is highly influenced by fly activity, with mature signaling males being subject to a majority of the attacks and suffering the highest losses on foliage, whereas on fruit it was ovipositing females that suffered the highest mortality. However, mature but virgin females also suffered considerable losses on foliage while visiting leking males. Mating pairs, even though they tended to leave the lek immediately after pair formation, suffered the highest predation losses proportionate to the number of attacks. Possible reasons for this activity- and sex-biased predation are discussed.

The hypothesis that Vespula germanica foragers can recruit nestmates to food resources was tested using a protocol that controlled for the biasing effects of social factors at the resource, including local enhancement and food-site marking substances. Foragers from an observation colony in the field were trained to visit a dish of scented corn syrup solution 15 m east of the nest. A second feeding station, 22 m northeast of the nest, offered incoming foragers a choice between food with the training scent and food with a control scent. Significantly more naive foragers arriving at that station chose the food with the training scent. We conclude that the German yellowjacket is able to recruit nestmates to carbohydrate food sources, and that recruits use food odor to locate the source of food being brought into the nest.

Excavations of 4 nests of the western yellowjacket, Vespula pensylvanica (Saussure) (Hymenoptera: Vespidae) in southern California revealed situations that deviated from the typical annual, single-queen life history of yellowjacket colonies. Three nests that were collected well after colony decline (in December through February) consisted of more queens than workers. An additional nest excavated in April (a time when nests are typically being initiated by single foundress queens) revealed a large polygynous nest that was rearing workers, males, and queens, was very active, and was entering its 3rd year. These life history traits show a plasticity of behavior expressed in the warmer regions of the range of V. pensylvanica and may be more common than previously recorded.

Summary The wings of many insects accumulate considerable wear and tear during their lifespan, and this irreversible structural damage can impose significant costs on insect flight performance and survivability. Wing wear in foraging bumblebees (and likely many other species) is caused by inadvertent, repeated collisions with vegetation during flight, suggesting the possibility that insect wings may display biomechanical adaptations to mitigate the damage associated with collisions. We used a novel experimental technique to artificially induce wing wear in bumblebees and yellowjacket wasps, closely related species with similar life histories but distinct wing morphologies. Wasps have a flexible resilin joint (the costal break) positioned distally along the leading edge of the wing, which allows the wing tip to crumple reversibly when it hits an obstacle, whereas bumblebees lack an analogous joint. Through experimental manipulation of its stiffness, we found that the costal break plays a critical role in mitigating collision damage in yellowjacket wings. However, bumblebee wings do not experience as much damage as would be expected based on their lack of a costal break, possibly due to differences in the spatial arrangement of supporting wing veins. Our results indicate that these two species utilize different wing design strategies for mitigating damage resulting from collisions. A simple inertial model of a flapping wing reveals the biomechanical constraints acting on the costal break, which may help explain its absence in bumblebee wings.

A thriving, polygynous, and probably overwintered colony of the western yellowjacket,Vespula pensylvanica, was collected on 2 November 1994 in Riverside, southern California, and examined in detail. The colony had 14 combs, of combined area 1.30 m2 containing 55,704 small and 10,266 large cells. There were 17 functional, physogastric queens, 70 newly emerged non-reproductive queens, 7300 adult workers, 685 adult males, and c. 17,600 capped cells containing pupae or fully-fed larvae. Dissections of 200 workers showed that none had well-developed ovaries. Hypotheses for the rarity of polygyny inVespula are put forward and evaluated.

Queens of the western yellowjacket, Vespula pensylvanica (Saussure), collected in the spring, founded nests under laboratory conditions. Of 24 queens collected, 11 initiated nests. Seven nests were transferred into observation hives, 5 produced workers which foraged outdoors, 4 developed multiple combs, and 2 reared reproductives. Flight activity and nest volume of the multiple-comb colonies were monitored weekly. Bionomic data on the multiplecomb nests were taken at either colony death or the end of the season. This project is a step toward the controlled rearing of colonies for behavioral observation, venom collection or biological control of agricultural pest insects.

The defensive behavior of colonies of Vespula pensylvanica (Saussure) and Bomhus sonorus Say is assayed with an easily-constructed electronic monitor that counts the number of impacts of insects attacking Ping-Pong ball targets. Black targets are attacked, and white targets are not. The administration of smoke to colonies before disturbing them greatly reduces the number of attacks. In B. sonorus, the reduction was >2-fold and in V. pensylvanica >10-fold. This suggests mechanisms of the effect of smoke besides those that have been described for honey bees. This effect may be useful to subdue these insects during insecticide treatments to destroy their nests.

Microbes are ubiquitous on plant surfaces. However, interactions between epiphytic microbes and arthropods are rarely considered as a factor that affects arthropod behaviors. Here, volatile emissions from an epiphytic fungus were investigated as semiochemical attractants for two eusocial wasps. The fungus Aureobasidium pullulans was isolated from apples, and the volatile compounds emitted by fungal colonies were quantified. The attractiveness of fungal colonies and fungal volatiles to social wasps (Vespula spp.) were experimentally tested in the field. Three important findings emerged: (1) traps baited with A. pullulans caught 2750 % more wasps on average than unbaited control traps; (2) the major headspace volatiles emitted by A. pullulans were 2-methyl-1-butanol, 3-methyl-1-butanol, and 2-phenylethyl alcohol; and (3) a synthetic blend of fungal volatiles attracted 4,933 % more wasps on average than unbaited controls. Wasps were most attracted to 2-methyl-1-butanol. The primary wasp species attracted to fungal volatiles were the western yellowjacket (Vespula pensylvanica) and the German yellowjacket (V. germanica), and both species externally vectored A. pullulans. This is the first study to link microbial volatile emissions with eusocial wasp behaviors, and these experiments indicate that volatile compounds emitted by an epiphytic fungus can be responsible for wasp attraction. This work implicates epiphytic microbes as important components in the community ecology of some eusocial hymenopterans, and fungal emissions may signal suitable nutrient sources to foraging wasps. Our experiments are suggestive of a potential symbiosis, but additional studies are needed to determine if eusocial wasp–fungal associations are widespread, and whether these associations are incidental, facultative, or obligate.

The German yellowjacket Vespula germanica (F.) (Hymenoptera: Vespidae), an invasive wasp, is a highly efficient forager. We studied wasp cognitive ability while varying landmark disposition and cue conspicuity. Learning flights were used as an indicator of forager cognition while relocating a food source. We recorded the number of learning flights (circling above the food location) performed after each visit by each wasp. We studied the effect of modifying a learned location and analyzed how the addition of conspicuous cues affected wasp learning. Cognitive ability also was studied in relation to food manipulation efficiency, i.e., the time taken to extract a piece of meat and fly away. We found that one feeding visit was sufficient for wasps to learn relevant cues associated with a rewarded location, as shown by the reduction of learning flights after just one experience. Moreover, wasps reached asymptotic levels in food manipulation after only one feeding visit. The introduction of a contextual change, such as moving the food location a few centimeters from the original feeding site, affected returning foragers, who increased the number of learning flights when leaving the array. Interestingly, enriched contexts with conspicuous cues seemed to facilitate wasp cognition as they performed fewer learning flights than in nonenriched ones. Learning flights seem to be a good cognitive indicator, reflecting wasp experience with a certain context, thus revealing their sensitivity to landmark cue conspicuity. This study highlights the cognitive capacities of V. germanica foragers. Fil: Moreyra, Sabrina Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Ecotono; Argentina Fil: D'adamo, Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Ecotono; Argentina Fil: Lozada, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Ecotono; Argentina

Ten yellowjacket species, of markedly different abundances, were found in a central Appalachian broadleaf forest from 1991 to 1993. Malaise-trap samples indicated that yellowjacket numbers fluctuated greatly between years, as occurs in other habitats. A split-plot analysis revealed that diflubenzuron decreased worker number in the application year but not in the postapplication year and revealed no effect of trap site on worker sample size.

The sperm content of the spermatheca was examined in eleven species of yellowjacket queens collected in the spring of 1987–1989. The sperm count data were highly correlated ( r = 0.84) with total cell numbers of mature nests reported for 10 species. Sperm content varied within and among species with mean numbers of sperm ranging from a low of 3,200 ± 600 in Vespula consobrina in 1988, to a high of 176,000 ± 46,200 in Vespula squamosa , the same year. The implications of mating success and initial sperm quantity variability are discussed.

Predation is probably the most important male mortality factor in insect species with courtship displays that render males performing them conspicuous targets of predators. Sexually active Mediterranean fruit fly males, Ceratitis capitata (Wied.), aggregate in leks, where they participate in agonistic encounters and engage in visual, acoustic and pheromone-calling displays to attract receptive females. The objective of this study was to assess: a) whether sexually displaying C. capitata males in leks inside host and non-host foliage are subject to predation by the most prominent predators yellow-jacket wasps, Vespula germanica (F.), and if so, b) whether olfactory, visual or auditive stimuli are used by foraging wasps in locating male C. capitata prey. Studies were carried out in a citrus orchard and surroundings on the island of Chios, Greece. Observations were conducted using perforated containers hung within mulberry, fig or citrus foliage. Living C. capitata flies of different sex and either mature or immature were placed inside. Our results show that the yellowjacket wasps have learned to associate the presence of sexually active medfly males aggregated in leks with their prey's pheromone (kairomone). Foraging wasps, flying through the crowns of host trees, responded to the odour source of C. capitata male pheromone by approaching from downwind. Even inside dense citrus tree foliage, wasps keyed in on aggregations of pheromone-calling males using olfactory stimuli. Stimuli of visual and acoustic male signalling were only used at close range, after having followed the pheromone plume close to its source. Visual cues played a greater role in directing wasp foraging under more open and exposed host foliage conditions. Odour-based foraging of wasps inside host foliage in the mid-morning hours, when medfly male lekking activities peak, shifted gradually to a more visual-based host fruit patrolling in the afternoons to capture ovipositing and feeding medfly females. On ripe fruit, particularly fig, V. germanica visual prey hunting also included the capture of feeding medfly males, other feeding Diptera, as well as medfly larvae extracted from wasp-made perforations in the fruit.

Variation in invasion success may result from the divergent evolutionary histories of introduced species compared to those of native taxa. The vulnerability of native biotas to ecological disruption may be especially great on oceanic islands invaded by continental species with unique ecological traits. In part because Hawaii lacks native eusocial insects, social invaders may threaten endemic taxa that are ecologically similar but solitary. Using a combination of field manipulations, molecular analyses, physiological data, and behavioral assays, we identify the mechanisms underlying the displacement of two genera of native solitary Hymenoptera in Hawaii by a social continental invader, the western yellowjacket (Vespula pensylvanica). Experimental removal of V. pensylvanica colonies resulted in increased densities of native Hymenoptera. Endemic Hylaeus bees directly suffer through predation by yellowjackets, and perhaps as a consequence, avoid floral resources occupied by V. pensylvanica. Native Nesodynerus wasps also avoid V. pensylvanica but are negatively affected by yellowjackets not through predation, but through exploitative competition for caterpillar prey. Displacement of native solitary Hymenoptera may be heightened by the ability of V. pensylvanica to prey upon and scavenge honey bees and to rob their honey stores, resources unavailable to endemic bees and wasps because of their specialized niches. Our study provides a unique example of an ecologically generalized social invader that restructures native assemblages of solitary Hymenoptera by interacting with endemic taxa on multiple trophic levels.

SUMMARY The difficulty of directly observing predatory events hinders a complete understanding of how predation structures food webs. Indirect approaches such as PCR-based and isotopic analyses clarify patterns of resource consumption but fail to distinguish predation from scavenging. Given that facultative scavenging is a ubiquitous and phylogenetically widespread foraging strategy, an improved ability to discriminate prey from carrion is needed to enhance an understanding of the demographic effects of consumption and the true nature of trophic interactions. Using physiological properties of muscle tissue – specifically pH and rate of water loss – we develop a novel method to discriminate prey from carrion collected by scavenging hymenopteran predators. Our focal system is the western yellowjacket (Vespula pensylvanica), a common scavenging predator in Hawaii and western North America. Prior to consumption, the physical properties of hymenopteran muscle tissue change in a quantifiable and deterministic manner post mortem and can be used to estimate the time and putative cause of death of diet items. Applying this method in laboratory and field situations resulted in the correct identification of prey and carrion in 49 out of 56 cases (88%). Although further investigation is needed to determine how post-mortem physiology of diet items changes in the guts of consumers, the approaches developed in this study can be used to distinguish predation from scavenging by central-place foragers (particularly arthropods). Such information will provide a more definitive characterization of species interactions and food webs.