Circulating hemocytes from larvae of the paper wasp Polistes dominulus (Hymenoptera, Vespidae)

Circulating hemocytes from larval stages of the paper wasp Polistes dominulus were characterized by light and transmission electron microscopy. Three types were identified: prohemocytes, plasmatocytes and granulocytes. The first two are agranular cells while the latter present typical cytoplasmic inclusions called granules. Plasmatocytes differ from prohemocytes being larger, showing lower nucleus/cytoplasm ratio and they possess many phagolysosomes. The substantial uniformity of most subcellular features and the presence of "intermediate forms" support the "single-cell theory" i.e., there is only one cell line that originates from the prohemocyte and leads to the granular cell passing through the plasmatocyte. This hypothesis seems to be confirmed by functional tests. Indeed, most part of cells adheres to the glass and is able to phagocytize fluorescent microspheres.     

Information analysis by the paper wasp,Polistes fuscatus,during nest construction (Hymenoptera,Vespidae)

Summary The building decision process of the paper wasp,Polistes fuscatus, was studied by 1) analyzing the search pattern of the wasps prior to the addition of pulp to different areas of the nest, 2) comparing the pulp addition needs of the cell chosen for lengthening to those of other cells in the nest, and 3) presenting the wasps with eight types of dichotomous building choices, which provided information about the relative influence of different building cues. Wasps conduct a hierarchical search prior to pulp addition, which means that they search the comb face and petiole disproportionately more often and more thoroughly than the comb back and sides. Once a particular nest area triggers closer scrutiny, comparisons are made with adjoining areas. The most needy location is then chosen based on nest cues. When lengthening a cell, the development of the brood and relative cell length have a strong influence on which cell is chosen at all times, while distance of the brood from the cell mouth becomes important during the later stages of brood development. The results indicate that there is no simple hierarchical weighting of cues. The decision process involves comparisons among multiple cues, which for the most part have an additive influence when variation in relative cue strength is considered.     

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.     

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.     

First detailed report of brood parasitoidism in the invasive population of the paper wasp Polistes dominulus (Hymenoptera, Vespidae) in North America

The European paper wasp Polistes dominulus (Christ) is a model system in the fields of behavioral ecology, ecological immunology, and invasion biology. Since its introduction to the US in 1978, its invasion success has been attributed, in part, to a lack of parasites or parasitoids infecting this population. This is despite the number of parasites which infest the native population and the generalist polistine parasites and parasitoids documented in sympatric North American species. Multiple studies have cited low parasite pressure as evidence that the invasive population of P. dominulus is benefiting from a post-invasion release from enemies. Here, we present the first well documented case of parasitoidism of the invasive population of P. dominulus in North America.     

Reaction of parasitoids of the paper wasp Polistes dominulus (Christ) (Hymenoptera, Vespidae, Polistinae) to the host distribution

The specific features of spatio-temporal organization of the parasitoid-host system in a heterogeneous environment was analyzed. The spatial distribution of ectoparasitoids in different habitat types of their host Polistes dominulus (Christ) (Hymenoptera, Vespidae) was found to be non-uniform. Latibulus argiolus (Rossi) (Hymenoptera, Ichneumonidae) prevailed in the host nests located in shelters, while Elasmus schmitti Ruschka (Hymenoptera, Eulophidae) prevailed in the nests attached to plants.     

Polistes dominulus (Hymenoptera: Vespidae) larvae possess their own chemical signatures

Social insects use cuticular hydrocarbons (CHCs) as recognition cues in a variety of social contexts, such as species and nestmate recognition. Discrimination of nestmates is an important requisite to avoid exploitation by unrelated individuals. In social wasps, use of CHCs in nestmate recognition has been demonstrated only among adults, whereas very little is known regarding brood recognition. We performed gas chromatography-mass spectrometry analyses of the CHCs of adults and larvae of the social wasp Polistes dominulus and found that larvae possess a characteristic chemical colony-specific pattern distinct from that of adults. Behavioural assays confirmed that these are recognized and discriminated by adults. Larval epicuticular substances are therefore sufficient for recognition of nestmate larvae by adults and demonstrate that wasps are able to discriminate between alien and nestmate larval odours.     

Seasonal dynamics of the phenotypic structure of a population of the paper wasp Polistes dominulus (Christ) (Hymenoptera, Vespidae)

Seasonal changes in the coloration of the clypeus, mesonotum, and abdomen were studied in populations of the paper wasp, Polistes dominulus (Christ) in southern Ukraine. The color patterns in the populations were found to be different before and after hibernation. The frequencies of color morphs observed in the autumns of different years are similar, while the frequencies observed in spring vary from year to year. A tendency for pleometrosis is manifested by females of different color morphs in different years. The nest usurpers have darker patterns of the clypeus. A polyfunctional role of the coloration and pattern is supposed.     

A role of the Dufour's gland in the dominance interactions of the paper wasp,Polistes fuscatus (Hymenoptera: Vespidae)

The Dufour's gland of the paper wasp, Polistes fuscatus,is a source of the cues used by dominant females to recognize the eggs laid by subordinates or nonnestmates on pre (worker)-emergence nests. When dominant wasps were presented with an egg covered with either (1) the Dufour's gland extract of a subordinate cofoundress, (2) the extract of an egg from the same subordinate, or (3) the solvent alone, the dominant female destroyed and replaced the eggs covered with the Dufour's extract significantly more frequently than the other eggs. Eggs with the extract of a nonnestmate's Dufour's gland were also eaten significantly more frequently than those with the solvent. Given similar choices, subordinates did not destroy any eggs. The Dufour's gland appears to have little or no role in communicating dominance directly among aggressively interacting cofoundresses.     

Hole repair and the influence of learning on nest repair in the paper wasp,Polistes fuscatus (Hymenoptera: Vespidae)

Two methods of hole repair used by the paper wasp, Polistes fuscatus,were examined and compared, and the hypothesis that nest repair behavior may improve with experience was tested. Similarly sized holes were repeatedly made in the sides of nests and the repair behavior of the nest residents was recorded. The distance of the hole from the cell mouth determined which repair method was used. In addition, both the amount of time for hole repair completion and the number of pulp loads used in making the repair decreased significantly with experience.     

Geographic variation in the status signals of Polistes dominulus paper wasps

Understanding intraspecific geographic variation in animal signals poses a challenging evolutionary problem. Studies addressing geographic variation typically focus on signals used in mate-choice, however, geographic variation in intrasexual signals involved in competition is also known to occur. In Polistes dominulus paper wasps, females have black facial spots that signal dominance: individuals wasps with more complex 'broken' facial patterns are better fighters and are avoided by rivals. Recent work suggests there is dramatic geographic variation in these visual signals of quality, though this variation has not been explicitly described or quantified. Here, we analyze variation in P. dominulus signals across six populations and explore how environmental conditions may account for this variation. Overall, we found substantial variation in facial pattern brokenness across populations and castes. Workers have less broken facial patterns than gynes and queens, which have similar facial patterns. Strepsipteran parasitism, body size and temperature are all correlated with the facial pattern variation, suggesting that developmental plasticity likely plays a key role in this variation. First, the extent of parasitism varies across populations and parasitized individuals have lower facial pattern brokenness than unparasitized individuals. Second, there is substantial variation in body size across populations and a weak but significant relationship between facial pattern brokenness and body size. Wasps from populations with smaller body size (e.g. Italy) tend to have less broken facial patterns than wasps from populations with larger body size (e.g. New York, USA). Third, there is an apparent association between facial patterns and climate, with wasp from cooler locations tending to have higher facial pattern brokenness than wasps from warmer locations. Additional experimental work testing the causes and consequences of facial pattern variation will be important, as geographic variation in signals has important consequences for the evolution of communication systems and social behavior.     

Dynamics of cuticular chemical profiles of Polistes dominulus workers in orphaned nests (Hymenoptera, Vespidae)

We analysed changes in cuticular hydrocarbon signatures of workers in orphaned colonies of the paper wasp Polistes dominulus. In natural conditions, workers and foundresses possess characteristic cuticular signatures, and foundresses are further distinguishable, both behaviourally and chemically, on the basis of their rank in a reproductive dominance hierarchy. In our study, several workers were found to develop their ovaries and produce cuticular signatures resembling those of dominant foundresses, while remaining workers possessed undeveloped ovaries and had cuticular blends characteristic of subordinate foundresses. Workers that did not develop their ovaries had changed epicuticular signatures, demonstrating that the mixture of hydrocarbons of worker individuals is strongly dependent on social role and environment. Our results suggest that the composition of epicuticular lipids is not determined at the pre-imaginal stage, and that physiological pathways leading to cuticular chemical changes are similar in foundresses and workers of P. dominulus.     

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     

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.     

Visual signals of status and rival assessment in Polistes dominulus paper wasps

Aggressive competition is an important aspect of social interactions, but conflict can be costly. Some animals are thought to minimize the costs of conflict by using conventional signals of agonistic ability (i.e. badges of status) to assess rivals. Although putative badges have been found in a range of taxa, little research has tested whether individuals use badges to assess potential rivals before they engage in aggressive contests. Here, choice trials were used to test how the variable black facial patterns in Polistes dominulus wasps are used during rival assessment. Focal wasps were given access to two patches of food, each guarded by a wasp whose facial pattern had been experimentally altered. Wasps chose food patches based on the facial pattern of the guard, preferring to challenge guards with facial patterns indicating a low level of quality, while avoiding guards with facial patterns indicating a high level of quality. Therefore, status badges play an important role during rival assessment; paper wasps use facial patterns alone to quickly assess the agonistic abilities of strangers.     

Sexual interactions and nestmate recognition in invasive populations of Polistes dominulus wasps

Many social insect species have mating systems or recognition abilities that minimize the chance of inbreeding. In haplodiploid systems, inbreeding is especially costly due to the production of sterile offspring such as diploid males. Diploid males (and their triploid offspring) have been identified in invasive populations of the paper wasp, Polistes dominulus, but to date have not been reported in its native populations. Due to the degree of genetic diversity in the invasive populations, it is unlikely that the production of these genetic ‘misfits’ is the result of a genetic bottleneck alone, but rather that errors in nestmate recognition may play a role. Here, we investigated sexual interactions and nestmate recognition in male and female P. dominulus. We observed nine types of behavioral interactions (55 h of behavioral observation consisting of 1,514 interactions) from triads of paper wasps composed of one gyne (female) and two males—one nestmate male and one non-nestmate male. The frequency of male- or female-initiated aggressive behavior did not differ between nestmates or non-nestmates. Non-nestmates were more likely to attempt to copulate with the gyne, but successful copulations were very rare and occurred between non-nestmates and nestmates. We discuss these results within the context of invasion biology.     

Can venom volatiles be a taxonomic tool for Polistes wasps (Hymenoptera,Vespidae)?

In the present study, we investigated whether venom volatiles have a species-specific composition and could possibly be used to discriminate between related paper wasp species. We compared venom volatile chemical profiles, obtained through gas chromatography-mass spectrometry analyses, of three non-parasitic European Polistes species ( P. dominulus , P. gallicus and P. nimphus ). The results show that the venom volatile composition is indeed species specific and can thus be a useful systematic tool.