Alternative Nesting Strategies of Polistine Wasps in a Subtropical Locale

Phylogenetic studies suggest that historically all paper wasps (Vespidae: Polistinae) in North America have tropical origins, but some species have adapted to survive temperate conditions. Subtropical climates, which are intermediate between temperate and tropical, allow a unique opportunity to study ancestral traits which can be retained or lost within populations, and ultimately elucidate the process of social wasp evolution. We investigated the phenology of paper wasps at study sites in subtropical Baton Rouge, USA, through nest searching and monitoring of nest parameters throughout the warm season (March–October). Across the year, two periods of nest initiation occurred: from March–May (early season nests, i.e., before the summer solstice), and from July–September (late season nests, after the solstice). We observed 240 Polistes nests from six species, of which 50.8% were initiated in early season and 49.2% in late season. In contrast, Mischocyttarus mexicanus rarely built late season nests and had longer early season colony duration than Polistes bellicosus and P. dorsalis, which built more nests in the late season than early. Across all species, late season nests had significantly shorter colony duration (~87.6 days) than early season nests (~166 days), and only P. bellicosus had fewer adults at peak population in late season nests than in early season nests. Results indicate both a bivoltine colony cycle in Polistes of subtropical climates, as well as differences in nesting strategies between genera.

Assemblages of Social Wasps (Hymenoptera, Vespidae, Polistinae) in the Veredas of Central Brazil

Social wasps are widely distributed in Brazil, and their distribution is intimately linked to habitats and the vegetation structure. Veredas (Brazilian Palm swamps) occur in moist soils and are characterized by the almost monodominant presence of Buriti palms (Maurítia flexuosa). The insect fauna of these environments is poorly known, especially in Central Brazil. Some studies assessing the diversity of social wasps were carried out in the State of Mato Grosso, however, there are no studies performed in the palm swamps of this region. Thus, we aim in this study to investigate the composition of wasp species in six vereda environments throughout 24 months of sampling, from august 2017 to July 2019; The specimens were collected using a sweep net, in 200m transects that were subdivided into 10 3m2 parcels. To attract the wasps, we sprayed each parcel (using a backpack sprayer) with an insect attractant made from five spoons of granulated sugar and one spoon of salt dissolved in 5 liters of water. After spraying the plot, we waited 10 minutes before starting the collections and stayed another 10 minutes to sample in each plot, totaling 200 minutes of sampling per palm swamp. A total of 1062 social wasp specimens were collected, distributed in 10 genera and 36 species. The most abundant species were Polybia cf. ruficeps xantops (Richards, 1978), Angiopolybia pallens (Lepeletier, 1836), Polybia rejecta (Lepeletier, 1836), and Mischocyttarus sp. 2, which accounted for 57% of the total collected specimens in the 60 parcels. The estimated richness for the Vereda environments was 38,88 ± 0,627, approximately 41% of the 88 species of Polistinae wasps found in the Cerrado of eastern Mato Grosso.

Temporal analysis of effective population size and mating system in a social wasp

Highly social species are successful because they cooperate in obligately integrated societies. We examined temporal genetic variation in the eusocial wasp Vespula maculifrons in order to gain a greater understanding of evolution in highly social taxa. First, we wished to test if effective population sizes of eusocial species were relatively low due to the reproductive division of labor that characterizes eusocial taxa. We thus estimated the effective population size of V. maculifrons by examining temporal changes in population allele frequencies. We sampled the genetic composition of a V. maculifrons population at three separate time points spanning a 13-year period. We found that effective population size ranged in the hundreds of individuals, which is similar to estimates in other, non-eusocial taxa. Second, we estimated levels of polyandry in V. maculifrons in different years in order to determine if queen mating system varied over time. We found no significant change in the number or skew of males mated to queens. In addition, mating skew was not significant within V. maculifrons colonies. Therefore, our data suggest that queen mate number may be subject to stabilizing selection in this taxon. Overall, our study provides novel insight into the selective processes operating in eusocial species by analyzing temporal genetic changes within populations.

Caste and wing loading in a social wasp (Hymenoptera, Vespidae, Dolichovespula maculata)

Variation in wing design and wing loading according to body weight is well studied across taxa of birds and flying insects. Comparable studies have not been made in the few insects that show substantial size variation within the same phenon of a single species. We examine body measures of adults of the social wasp Dolichovespula maculata (Linnaeus, 1763), with particular attention to the limbs and wing loading. As expected, measures of the length of the legs scales isometrically with overall body weight and size. Against expectation, wing size also scales isometrically with body weight and size. This does not match the general pattern of comparison across species of flying animals, in which larger individuals have relatively larger wings, as a partial compensation for greater wing loading. We suggest that wing size in D. maculata may be constrained by the demands of life in a crowded nest.

Microbiome of the wasp Vespula pensylvanica in native and invasive populations, and associations with Moku virus

Invasive species present a worldwide concern as competition and pathogen reservoirs for native species. Specifically, the invasive social wasp, Vespula pensylvanica, is native to western North America and has become naturalized in Hawaii, where it exerts pressures on native arthropod communities as a competitor and predator. As invasive species may alter the microbial and disease ecology of their introduced ranges, there is a need to understand the microbiomes and virology of social wasps. We used 16S rRNA gene sequencing to characterize the microbiome of V. pensylvanica samples pooled by colony across two geographically distinct ranges and found that wasps generally associate with taxa within the bacterial genera Fructobacillus, Fructilactobacillus, Lactococcus, Leuconostoc, and Zymobacter, and likely associate with environmentally-acquired bacteria. Furthermore, V. pensylvanica harbors—and in some cases were dominated by—many endosymbionts including Wolbachia, Sodalis, Arsenophonus, and Rickettsia, and were found to contain bee-associated taxa, likely due to scavenging on or predation upon honey bees. Next, we used reverse-transcriptase quantitative PCR to assay colony-level infection intensity for Moku virus (family: Iflaviridae), a recently-described disease that is known to infect multiple Hymenopteran species. While Moku virus was prevalent and in high titer, it did not associate with microbial diversity, indicating that the microbiome may not directly interact with Moku virus in V. pensylvanica in meaningful ways. Collectively, our results suggest that the invasive social wasp V. pensylvanica associates with a simple microbiome, may be infected with putative endosymbionts, likely acquires bacterial taxa from the environment and diet, and is often infected with Moku virus. Our results suggest that V. pensylvanica, like other invasive social insects, has the potential to act as a reservoir for bacteria pathogenic to other pollinators, though this requires experimental demonstration.

Different trophic positions among social vespid species revealed by stable isotopes

The social vespid wasps are common insect predators and several species behave in unison in the same biotopes. It is commonly accepted that social wasps are mainly opportunistic generalist predators without differences in prey selection and hence they compete for the same food resources. Trophic positions of six vespid wasp species and their potential prey from four sites in Finland and one in the UK were evaluated using carbon and nitrogen stable isotopes (δ 13 C and δ 15 N). The difference in isotope values indicated different trophic positions among species. In general, Dolichovespula spp. showed higher δ 15 N values than Vespula spp., which suggests that Dolichovespula forage on higher trophic levels. Dolichovespula media (Retzius, 1783) showed the highest δ 15 N values, whereas Vespula vulgaris showed the lowest. Dolichovespula media partly expresses apex predator-like δ 15 N values, whereas Vespula species tend to forage on primary consumers. The largest species Vespa crabro (Linnaeus, 1758) showed also similar δ 15 N values as Vespula spp. However, δ 13 C and δ 15 N values of V. vulgaris workers varied slightly during the season. This study offers novel insights about the trophic segregation in the social wasp community, suggesting specialization in diet resource utilization, especially between Dolichovespula and Vespula .