Simulated Intraspecific Usurpations in Paper Wasps: Different Reproductive Tactics Affect Foreign Brood Destruction in Polistes fuscatus and Polistes dominulus

We simulated intraspecific usurpation in two species of paper wasps at a field site in Michigan to compare the species' treatment of foreign brood. Queens of Polistes fuscatus, a species that commonly uses intraspecific usurpation as an alternative reproductive tactic, destroyed significantly fewer large larvae and significantly more small larvae than queens of P. dominulus, a sympatric species that rarely usurps. The pattern of brood destruction exhibited by P. fuscatus was consistent with the previously published findings that P. fuscatus usurpers destroy reproductive‐destined brood (eggs and small larvae), but not worker‐destined brood (large larvae and pupae) that are subsequently used by a usurper to raise her own reproductives. The pattern of brood destruction displayed by P. dominulus differed from that of Polistes species that frequently engage in intraspecific usurpation. The brood destruction pattern in P. dominulus may have been shaped by nest adoption, a common alternative reproductive tactic in this species. If so, it is not clear why P. dominulus would destroy large, worker‐destined larvae.     

A ten-year comparative study of the population dynamics and parasitoidism in the native paper wasp Polistes fuscatus and the invasive P. dominulus

The invasive success of Polistes dominulus in North America has been attributed to its greater productivity relative to native Polistes. Liberation from parasites and parasitoids are thought to be major factors contributing to the high productivity of P. dominulus. We analyzed historical records of colony relative abundance and productivity of P. dominulus and the sympatric, native Polistes fuscatus from 1995 to 2010 using historical data from our Michigan Polistes study site. We also analyzed evidence of parasitoids from 294 P. fuscatus and 507 P. dominulus archived combs from 2001 to 2010. Additionally, we examined field and laboratory colonies from outside of our study site for parasites and parasitoids in 2009 and 2010. We documented one parasite and three parasitoids exploiting Polistes in our Michigan study sites. Our historical records document that P. dominulus initially displaced P. fuscatus rapidly, then slowed, and finally the two populations stabilized. Furthermore, the historical pattern of decreasing displacement of P. fuscatus by P. dominulus corresponded temporally with a significant decline in the productivity and a significant increase in Dibrachys cavus infestation of P. dominulus. Our evidence indicates that the parasitoid, D. cavus, is a major factor in stabilizing the populations of the sympatric P. dominulus and P. fuscatus.     

Rearing conditions influence quality signals but not individual identity signals in Polistes wasps

Given the diversity of animal signals, there has been recentinterest in categorizing signals into probable functions accordingto their properties. For example, models predict that signalsof quality should be costly and condition dependent, whereassignals of individual identity should be cheap and expressedindependently of condition. Here, we test these predictionsby comparing the condition dependence of signals of individualidentity and quality in Polistes wasps. Polistes fuscatus waspshave black and yellow patterns on the face and abdomen thatsignal individual identity, whereas Polistes dominulus waspshave black and yellow facial patterns that signal aspects ofquality related to dominance. We reared both species with andwithout supplemental food and examined the facial patterns ofthe resulting offspring. As predicted, food availability didnot influence the development of identity signals in P. fuscatus.In strong contrast, P. dominulus wasps reared with supplementalfood had facial patterns that signaled higher levels of qualitythan P. dominulus reared without supplemental food. Interestingly,the identity and quality signals have different condition dependence,despite being composed of similar pigments, suggesting thatsignal function has a stronger influence on signal propertiesthan pigmentation. Because body size is often correlated withquality signal elaboration, we also tested how food supplementationinfluenced offspring size. In both species, supplemented coloniesproduced smaller offspring than nonsupplemented colonies, suggestingthat queens may invest in producing fewer, larger offspringin stressful environments.     

Uniformity of Leaf Shelter Construction by Larvae of Epargyreus clarus (Hesperiidae), the Silver-Spotted Skipper

Larvae of the silver-spotted skipper, Epargyreus clarus (Hesperiidae), construct shelters from leaves of their leguminous host plants, making four distinct shelter types that change predictably over larval ontogeny. Shelters built by first-instar larvae are located on the apical half of the leaflet and are almost invariant in size, shape, and orientation, suggesting a stereotypical process of shelter location and construction. We have determined that the regularity of these shelters results from a prescribed pattern of larval movements and behaviors, in which larvae use their body length as a ruler and employ silk not only as a building material but also as a template to guide the location of cuts in the leaf. Though lepidopteran larvae lack the sensitive antennae, long jointed appendages, and other measurement devices used by structure-building bees, wasps, and caddis flies, they can nonetheless use simple tools and behavioral patterns to produce characteristic and regular shelters.     

The comparative biology of two sympatric paper wasps, the native Polistes fuscatus and the invasive Polistes dominulus (Hymenoptera, Vespidae)

Summary: Polistes dominulus (Christ), an old world paper wasp, was introduced accidentally into the eastern coast of the United States in the late 1970s and has been rapidly spreading westward, displacing the native P. fuscatus (F.). The biology of naturally nesting P. fuscatus and P. dominulus was compared at a field site in Rochester, Michigan. The basic methodology consisted of simultaneously videotaping spatially proximate, matched single-foundress colonies of P. fuscatus and P. dominulus (13 matched sets, 176.8 h of videography). In addition, extensive surveys and censuses were taken of colonies to record colony productivity, dates of nest initiation and first worker emergence, usurpation and parasitism.¶There was no evidence that P. dominulus is negatively impacting P. fuscatus through direct, agonistic encounters. However, P. dominulus is 4-5 times more productive than P. fuscatus, suggesting that P. dominulus is replacing P. fuscatus via exploitative competition. P. dominulus appears to have a number of advantages over P. fuscatus, including earlier production of workers, higher per capita foraging rates by queens and workers, higher queen survivorship, and lack of conspecific pressures. Nest site and/or prey availability may be limiting factors in the competition between the two species.     

Female Choice and Mating System of the Brown Capuchin Monkey Cebus apella (Primates: Cebidae)

Antennal drumming, in which Polistes queens rapidly beat the antennae on the rims of nest cells, is described in detail for P. fuscatus and shown to be performed in the context of feeding prey to the larvae. Following the distribution of solid food to the larvae, the queen goes from cell to cell on the nest, drumming her antennae on the cell rims, producing an audible sound. After several min of this, each drum on a cell is followed by contact with a larva, usually the one in the drummed cell, during which the queen regurgitates prey juice to the larva. The average burst of drumming lasts just under one s. The two antennal flagella strike the cell rim together at an average frequency of 29 strokes per s. Similar behavior is documented in 10 other Polistes species. We hypothesize that antennal drumming communicates to the larva that it is about to receive liquid food from the adult and should withhold the release of salivary secretion. This predicts that a larva that has received the drumming signal will exude less secretion than if it has not been recently signaled. An experimental test of this hypothesis yielded the predicted result, and we therefore conclude that our hypothesis is supported.     

A role for thermoregulation in the <Emphasis Type="Italic">Polistes dominulus</Emphasis> invasion: a comparison of the thermoregulatory abilities of the invasive wasp <Emphasis Type="Italic">P. dominulus</Emphasis> and the native wasp <Emphasis Type="Italic">P. fuscatus</Emphasis>

Social insects are excellent invaders that have had negative impacts on native species and humans. Many invasive species move from warmer to cooler climates. For these species, thermal adaptations may both be important for their ability to invade and to limit their invasion range. The invasion of Polistes dominulus into North America provides an example of a primitively eusocial invader from a warmer climate. We studied the differences in thermoregulation between P. dominulus and the native P. fuscatus. We found that, during flight, thorax temperature in P. fuscatus was less affected by ambient temperature than thorax temperature of P. dominulus. We also found that P. dominulus and P. fuscatus showed different patterns of warming after removal from a cold environment. Unlike P. dominulus, live P. fuscatus never fully cooled down in a cold environment. P. fuscatus also reached their relative minimum flight temperatures earlier than P. dominulus, but P. dominulus maintained higher elevated temperatures for longer. These differences in thermoregulatory ability suggest that the lower winter survival of P. dominulus could be offset by a greater thermal tolerance during flight, while the lower thermal tolerance of P. fuscatus in flight is offset somewhat by better thermoregulatory ability.     

Direct and indirect effects of predatory wasps (Polistes sp.: Vespidae) on gregarious caterpillars (Hemileuca lucina: Saturniidae)

Summary We examined how predation by vespid wasps,Polistes dominulus andP. fuscatus, affected the behavior, growth rate and survivorship of aggregated caterpillars ofHemileuca lucina (Saturniidae). Although these larvae can exhibit a variety of defense and escape behaviors, in general larvae reacted to wasp attacks by clinging to the hostplant. Neighboring larvae in the aggregation responded by leaving the feeding site and moving to the interior or base of the plant. To determine wheter wasp attack affected the behavior and growth of the caterpillars that escaped, a field experiment was conducted with treatments of: 1) larvae exposed to wasps, 2) larvae protected from wasps, and 3) larvae protected from wasps but with the attack of wasps simulated (=harassment). Over just one instar, protected larvae gained significantly more weight than the harassed larvae, which in turn weighed significantly more than the larvae that escaped the wasps. The behavior of attacked and harassed larvae differed from that of the protected larvae; the disturbed larvae often fed in smaller groups and in shaded portions of the plant where only mature leaves were available. A laboratory experiment showed that at 35° C (daytime temperature) larvae had significantly higher relative growth rates and significantly shorter instar duration than larvae reared at 25° C. Our results suggest that wasps, in addition to killing caterpillars, indirectly affect larval fitness by slowing larval growth, at least in part by forcing larvae into cooler microhabitats where leaves are of lower quality.     

The comparative biology of two sympatric paper wasps in Michigan,the native <Emphasis Type="Italic">Polistes fuscatus</Emphasis> and the invasive <Emphasis Type="Italic">Polistes dominulus</Emphasis> (Hymenoptera,Vespidae)

Summary The biology of the invasive Polistes dominulus and the native P. fuscatus was compared at a field site in Rochester, Michigan over a two-year period. Colonies nesting semi-naturally in plywood nestboxes were studied using videography, extensive surveys, and colony-specific marking of gynes.Both single- and multiple-foundress colonies of P. dominulus were significantly more productive than comparable colonies of P. fuscatus. The disparity in productivity was significantly more pronounced in single-foundress colonies than in multiple-foundress colonies. P. dominulus had significantly shorter larval and pupal development times than P. fuscatus, which allowed P. dominulus to produce its first workers about a week earlier than P. fuscatus. P. dominulus had a number of additional advantages over P. fuscatus that contributed to its productivity including (1) significantly less parasitism by Strepsiptera, (2) significantly greater probability of renesting after predation by raccoons, (3) significantly lower usurpation pressures, and (4) possibly longer foraging days . The recovery of colony-marked foundresses indicated that gynes of P. dominulus suffered significantly greater mortality than gynes of P. fuscatus during winter diapause and that foundresses of both species were equally, strongly philopatric.P. dominulus is likely replacing P. fuscatus in many areas of southeastern Michigan via indirect or exploitative competition. The two species may be competing for nest sites.Received 7 July 2003; revised 10 October 2003; accepted 3 November 2003.     

Nest recognition in neighboring colonies: a comparison of two European species of Polistes wasps (P. dominulus and P. nimphus, Hymenoptera: Vespidae)

The ability of two species of Polistes wasps to distinguish their own from nearby nests was tested, following the procedure used by Espelie et al. Our experiments demonstrated that, in the laboratory, females of Polistes dominulus and Polistes nimphus preferentially selected their own nests rather than nearby nests. We also evaluated the role of odor cues in nest recognition by washing nests in hexane to remove the apolar solvent-soluble components of nest odor. Although P. nimphus females continued to discriminate nests even after washing, P. dominulus individuals failed to discriminate between their own and a foreign neighboring nest. In both species, wasps were able to recognize their own nests when nest extracts were subsequently reapplied to the nest surface. These results indicate that P. dominulus wasps recognize their nests through perception of nest odor. The ability of P. nimphus wasps to distinguish their own nests even after presumed removal of the nest odor is discussed. Received: January 27, 2000 / Accepted: May 22, 2000     

Roles for structural and temporal shelter-changing by fern-feeding lepidopteran larvae

Summary Larvae of the pyralid moth, Herpetogramma aeglealis, construct feeding shelters upon the Christmas fern (Polystichum acrostichoides). Field and laboratory study involving 532 shelters showed that as the larvae mature, they sequentially inhabit approximately 5 shelters of 3 distinct types, constructed at night on different fronds of the same plant. The bundle shelter, simple and ephemeral, is first to be inhabited and constructed. The fiddlehead shelter which houses slightly older larvae strongly resembles contemporaneously emerging frond fiddleheads. The final shelter form, the globe, is a silk-bound ball of leaflets at the frond tip. An individual larva usually constructs 3 globe shelters on different fronds of the same plant before completing its development. As shelter sites, sterile Polystichum fronds are chosen preferentially over fertile fronds. The bundle and fiddlehead shelter forms, less abundant, appear cryptic to humans and perhaps to other vertebrates. The final globe shelter form is larger and quite conspicuous. However, the persistence of empty globe shelters left on the plant as the larva moves to a new one may serve to make searching for larvae less profitable for potential predators and parasites. We suggest that the energetic costs of constructing and occupying multiple shelters may be offset by circumvention of reduced frond palatability and reduced exposure to predators and parasites.     

Nest site competition between cavity nesting passerines and golden paper wasps Polistes fuscatus

Nest boxes provide sheltered nesting sites for both passerines and paper wasps. Although neither wasps nor birds appear to evict the other once one is fully established, it is unclear which is the dominant competitor at the onset of the breeding season. Using wire mesh, we excluded birds but not golden paper wasps Polistesfuscatus from alternating boxes along a transect through edge habitat in North Carolina from 2006 – 2008. If wasps dominate Carolina chickadees Poecile carolinensis and eastern bluebirds Sialia sialis during the early spring (all have similar nest initiation dates), we would expect wasps to settle in both box types at equal frequencies. However, if birds dominate wasps, we would expect wasp nests to be concentrated in “bird‐proof” boxes. We found wasps in bird‐proof boxes significantly more often than in bird‐accessible boxes, indicating that secondary‐cavity nesting birds are able to exclude wasps from available nest sites. Additionally, we found that during the period of nest initiation, birds usurp wasps more often than vice versa.     

Larval sex identification in the paper wasp <Emphasis Type="Italic">Polistes dominulus</Emphasis> (Vespidae,Hymenoptera)

Identifying the sex of larvae is important in social Hymenoptera. Until now for Polistes wasps it has been necessary to genotype larvae at microsatellite loci, and assign their sex based on homozygosity at these loci. In our study on the paper wasp Polistes dominulus we have found morphological differences between larval sexes that can be used for larvae from the 3^rd instar on to easily and cheaply identify larval sex: the external gonopore and the shape and size of larval gonads. The robustness of these indicators was supported by genotype data at four microsatellite loci. Using gonopore and gonad features for sex assignment will assign diploid males as males, unlike techniques based on genetic loci or chromosomes. Received 12 July 2006; revised 4 January 2007; accepted 5 February 2007.     

Selection for individual recognition and the evolution of polymorphic identity signals in Polistes paper wasps

Individual recognition (IR) requires individuals to uniquely identify their social partners based on phenotypic variation. Because IR is so specific, distinctive phenotypes that stand out from the crowd facilitate efficient recognition. Over time, the benefits of unique appearances are predicted to produce a correlation between IR and phenotypic variation. Here, we test whether there is an association between elevated phenotypic polymorphism and IR in paper wasps. Previous work has shown that Polistes fuscatus use variable colour patterns for IR. We test whether two less variable wasp species, Polistes dominulus and Polistes metricus, are capable of IR. As predicted, neither species is capable of IR, suggesting that highly variable colour patterns are confined to Polistes species with IR. This association suggests that elevated phenotypic variation in taxa with IR may be the result of selection for identity signals rather than neutral processes. Given that IR is widespread among social taxa, selection for identity signalling may be an underappreciated mechanism for the origin and maintenance of polymorphism.     

Individual recognition is associated with holistic face processing in Polistes paper wasps in a species-specific way

Most recognition is based on identifying features, but specialization for face recognition in primates relies on a different mechanism, termed ‘holistic processing’ where facial features are bound together into a gestalt which is more than the sum of its parts. Here, we test whether individual face recognition in paper wasps also involved holistic processing using a modification of the classic part-whole test in two related paper wasp species: Polistes fuscatus, which use facial patterns to individually identify conspecifics, and Polistes dominula, which lacks individual recognition. We show that P. fuscatus use holistic processing to discriminate between P. fuscatus face images but not P. dominula face images. By contrast, P. dominula do not rely on holistic processing to discriminate between conspecific or heterospecific face images. Therefore, P. fuscatus wasps have evolved holistic face processing, but this ability is highly specific and shaped by species-specific and stimulus-specific selective pressures. Convergence towards holistic face processing in distant taxa (primates, wasps) as well as divergence among closely related taxa with different recognition behaviour (P. dominula, P. fuscatus) suggests that holistic processing may be a universal adaptive strategy to facilitate expertise in face recognition.     

The Polistes war: weak immune function in the invasive P. dominulus relative to the native P. fuscatus

Invasive species are of growing ecological concern, in part because of conflicts arising with native congeners. The European paper wasp Polistes dominulus was first introduced to North America in the 1970s, and may be displacing at least one native species, P. fuscatus. Previous reports indicate that in native territories over half of P. dominulus colonies are infected by Strepsipteran parasites, which decrease host fitness. In North America, P. fuscatus are parasitized to a lesser degree (approximately one-third), but no infected colonies of invasive P. dominulus have been reported. Because immune function is an indicator of susceptibility to parasitism, we quantified activated levels of immune function by measuring the encapsulation response and phenoloxidase activity and then compared these levels between species. Counterintuitively, our results indicate that P. dominulus has lower levels of both mechanisms of immunity. Additionally, P. dominulus displayed less self-grooming activity than P. fuscatus. We briefly discuss possible immunological explanations for this invasion success, including the selective expression of low immunocompetence.     

The cost of flight: a role in the <Emphasis Type="Italic">Polistes dominulus</Emphasis> invasion

Polistes dominulus is a primitively eusocial paper wasp from Mediterranean Europe that is invasive to North America. In Eastern North America, P. dominulus is in competition with P. fuscatus. One reason for the success of P. dominulus is that their colonies produce more reproductive offspring than P. fuscatus colonies. A partial explanation for this difference is that P. dominulus foundresses make more foraging trips in the pre-worker period, which likely helps them to rear workers more quickly. In comparing the species, we found that P. dominulus had a lower absolute flight metabolic rate, but that P. fuscatus had a lower mass-specific flight metabolic rate. In addition, in P. fuscatus, wingloading correlated with flight metabolic rate, but that this was not the case in P. dominulus. This suggests that P. fuscatus is not able to transport large loads inexpensively. Therefore, the lower overall cost of transport of P. dominulus may provide an advantage by allowing the foundresses to make more relatively efficient foraging trips. In addition, we compared time in flight by P. dominulus and P. fuscatus over a range of temperatures and found that while P. fuscatus flew well over a broad range of temperatures, P. dominulus had a relatively narrow range of optimal temperatures for flight (30–33°C). These differences may help explain both the success and the limitations of the P. dominulus invasion.     

The effect of juvenile hormone on temporal polyethism in the paper wasp Polistes dominulus

Juvenile hormone (JH) has an important role in the behavior of eusocial Hymenoptera. Previous work has shown that JH influences aggression and dominance behavior in primitive eusocial insects that lack discrete queen and worker castes (e.g. Bombus bees and Polistes wasps). In contrast, JH is one of the factors that mediates temporal polyethism among workers in advanced eusocial insects that have reproductive castes (e.g. Apis bees and Polybiawasps). Therefore, initial observations suggest that JH may have different roles in primitive and advanced eusocial taxa. Here, we use detailed behavioral observations of marked individuals to test whether JH influences temporal polyethism in the primitive eusocial wasp Polistes dominulus. First, we show that workers in P. dominulus have an age-related division of labor, as workers switch from nest work to foraging as they mature. Then, we show that application of JH accelerates the onset of foraging behavior.Workers treated with JH start foraging at a younger age than control workers. Therefore, JH mediates temporal polyethism in the primitively eusocial insect Polistes dominulus. Received 23 April 2008; revised 6 August 2008; accepted 11 August 2008     

A novel method for protecting slow-release sachets of predatory mites against environmental stresses and increasing predator release to crops

Slow-release sachets of predatory mites are widely employed for controlling small pest arthropods in protected crops. However, environmental stresses can adversely affect the performance of such sachets. To solve this problem, we developed plant-attached shelters that hold sachets of Neoseiulus californicus (McGregor) or Amblyseius swirskii (Athias-Henriot). We conducted laboratory experiments to reveal whether sheltered sachets can protect predators against pesticides and drenching. The numbers of each predator in unsheltered sachets were drastically decreased after spraying with a non-selective pesticide (methidathion), and after continuous spraying (four days) with water, whereas the numbers in the sheltered sachets were not seriously affected by these factors. We also found that more predators (at least for N. californicus) were released from sheltered sachets at different temperatures (25 and 17 °C) than from unsheltered sachets. These results indicate sheltered sachets to be potentially useful for protecting predatory mites against environmental stresses and enhancing their release to crops.     

Ecological consequences of shelter sharing by leaf-tying caterpillars

A wide variety of insect herbivores construct and inhabit leaf shelters (ties, rolls, folds, and webs). Shelter construction can lead to a high rate of secondary occupation by other arthropods, including other species of constructors. The consequences for the inhabitants of secondarily occupying these shelters are currently unknown. In this study, we conducted field experiments to examine the fitness consequences (survival and attack by natural enemies) for caterpillars that (i) occupy a shelter with conspecifics vs. occur singly; and (ii) establish a new shelter vs. colonize a pre‐existing one. In addition, we conducted factorial laboratory experiments to test the hypothesis that caterpillars sharing shelters with conspecifics might have reduced construction costs (a potential benefit of shelter‐sharing or secondary occupation). Larvae of Psilocorsis quercicella Clemens (Lepidoptera: Oecophoridae) placed in white oak [Quercus alba L. (Fagaceae)] leaf ties alone or in groups of three had equal likelihood of survival from natural enemies. This same caterpillar species, however, had a higher disappearance rate when placed in pre‐existing leaf ties than when placed in newly formed ones, suggesting a potential cost of secondary colonization. A similar experiment with a closely related species [Psilocorsis cryptolechiella (Chambers)], however, failed to detect a cost of secondarily occupying shelters made on beech, Fagus grandifolia Ehrh. (Fagaceae). In the laboratory experiment, we found no evidence of shelter‐sharing benefits; rather larvae reared in shelters in groups of three had lower pupal mass (and thus lower potential fecundity) than larvae reared singly, suggesting a cost of shelter sharing. Moreover, groups of larvae forced to repeatedly construct new shelters tended to have reduced survival relative to the other treatment, suggesting that energetic constraints are more likely to reduce fitness when larvae cohabit shelters. Taken together, these results indicate that the common phenomenon of shelter sharing by leaf‐tying caterpillars has either neutral or negative effects for the occupants. The fact that these leaf‐tying caterpillars actually share shelters may simply reflect limited availability of oviposition sites.