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.

Origin of an evolutionary novelty: the worker phenotype of eusocial wasps

Complex problems in evolutionary biology can be approached in two ways, top down using theoretical constructs and bottom up using empirical studies . Theoretical concepts predominate evolutionary interpretations of eusociality in a literature that is small relative to an enormous literature of natural history and basic research that is not synthesized into a conceptual whole. Here, I draw insights from this literature to show how paper wasps’ allomaternal non-reproductive worker phenotype originates in every colony cycle via confluence of multiple factors of paper wasp biology. These include behavior, development, nutrient dynamics, indirect genetic effects, sex ratio, and demography. A novel perspective on the colony cycle, based on individuals’ reproductive physiology, serves as context to examine of each of these. It will be shown that the allomaternal non-reproductive worker phenotype does not require relatedness among colony members to originate. Allomaternal care of non-relatives is frequent and can occur in at least twelve contexts. Life histories of living species as they will be presented here show that relatedness among colony members is not the target of selection in simple eusociality. However, the novel allomaternal non-reproductive worker phenotype had to be present at the ancestral origins of complex eusociality in which relatedness among colony members is essential.

Pollen Diet Composition Impacts Early Nesting Success in Queen Bumble Bees Bombus impatiens Cresson(Hymenoptera: Apidae)

Bumble bees are generalist pollinators that typically collect floral rewards from a wide array of flowering plant species. Among the greatest threats to wild bumble bee populations worldwide, many of which are declining, is a loss of floral resource abundance and diversity in the landscapes they inhabit. We examined how composition of pollen diet impacts early nesting success in laboratory-reared queens of the bumble bee Bombus impatiens. Specifically, we provided queens and their young nests with one of three pollen diets, each of which was dominated by a single pollen type, and explored how this diet treatment influenced the length of time until queens initiated nests, total counts of brood in the nest at the end of the experiment (8 wk later), and the size and weight of adult offspring produced. We found that the amount of later-stage brood (pupae and/or adults) produced by recently-initiated nests was strongly impacted by pollen diet. For example, on average 66% fewer later-stage brood were found in nests provided with the Cistus pollen Linnaeus (Cistaceae), relative to the predominantly Asteraceae pollen. This finding suggests that particular pollen diet compositions may delay larval growth, which delays colony development and may ultimately be detrimental for young nests. This study sheds light on how one of the leading stressors for bumble bees (nutritional stress) may negatively impact populations through its influence on brood production during the nest-founding stage of the colony cycle.

Social regulation of insulin signaling and the evolution of eusociality in ants

Queens and workers of eusocial Hymenoptera are considered homologous to the reproductive and brood care phases of an ancestral subsocial life cycle. However, the molecular mechanisms underlying the evolution of reproductive division of labor remain obscure. Using a brain transcriptomics screen, we identified a single gene,insulin-like peptide 2(ilp2), which is always up-regulated in ant reproductives, likely because they are better nourished than their nonreproductive nestmates. In clonal raider ants (Ooceraea biroi), larval signals inhibit adult reproduction by suppressingilp2, thus producing a colony reproductive cycle reminiscent of ancestral subsociality. However, increasing ILP2 peptide levels overrides larval suppression, thereby breaking the colony cycle and inducing a stable division of labor. These findings suggest a simple model for the origin of ant eusociality via nutritionally determined reproductive asymmetries potentially amplified by larval signals.

Neotropical Swarm-Founding Wasps (Vespidae: Polistinae: Epiponini) Accept Expelled Queens in Case of Queen Loss

In the Epiponini, queen number declines through colony cycle, becausesome queens are expelled from colonies. Here we demonstratethat Epiponini wasps may accept expelled queens in situations ofqueenlessness. One colony of Protopolybia exigua was observed at theUniversity of São Paulo in Brazil; and another of Metapolybia docilis wasobserved at La Selva Biological Station in Costa Rica. Queen removaltests were performed to study workers’ acceptance of expelled queensand queens from other colonies. In P. exigua, the experimental queenelimination caused a change in the workers’ behavior, ranging fromaggressive expulsion of non-selected queens to re-acceptance. In M.docilis workers were willing to accept queens from other colonies afterqueen elimination. Our results indicate that because of a decrease inworkers aggressiveness during the colony cycle, workers may acceptexpelled queens (even foreign ones, in experimental situations) in orderto ensure colony survival.

Effects of neonicotinoid insecticide exposure and monofloral diet on nest-founding bumblebee queens

Bumblebees are among the world's most important groups of pollinating insects in natural and agricultural ecosystems. Each spring, queen bumblebees emerge from overwintering and initiate new nests, which ultimately give rise to workers and new reproductives later in the season. Nest initiation and survival are thus key drivers of both bumblebee pollination services and population dynamics. We performed the first laboratory experiment with the model bumblebee species Bombus impatiens that explores how early nesting success is impacted by the effects of temporary or more sustained exposure to sublethal levels of a neonicotinoid-type insecticide (imidacloprid at 5 ppb in nectar) and by reliance on a monofloral pollen diet, two factors that have been previously implicated in bumblebee decline. We found that queens exhibited increased mortality and dramatically reduced activity levels when exposed to imidacloprid, as well as delayed nest initiation and lower brood numbers in the nest, but partially recovered from these effects when they only received early, temporary exposure. The effects of pollen diet on individual queen- and colony-level responses were overshadowed by effects of the insecticide, although a monofloral pollen diet alone was sufficient to negatively impact brood production. These findings speak to the sensitivity of queen bumblebees during the nest initiation phase of the colony cycle, with implications for how queens and their young nests are uniquely impacted by exposure to threats such as pesticide exposure and foraging habitat unsuitability.

Comparative Study of the Development of Mischocyttarus cassununga Von Ihering and Mischocyttarus cerberus styx Richards Colonies (Hymenoptera, Vespidae, Mischocyttarini)

Mischocyttarus is a genus of eusocial wasps belonging to the Polistinae subfamily. They build nests without envelopes, making it easier to take notes and follow the growth of the nest, allowing the observation of oviposition, development of the eggs, larvae and pupae, as well as the addition of new cells to the nest and hierarchical conflicts among adults. Mischocyttarus cerberus styx Richards and Mischocyttarus cassununga Von Ihering are representatives of a genus and tribe that occur only in the Americas and these species happen to occur in the municipality of Rio Claro (SP). The present work aimed to follow the development of colonies in order to develop a comparative approach of factors that interact with the colony cycle, to verify if the species show similar or diverse profiles from each other. Four locations were chosen to represent the sampling at the Universidade Estadual Paulista campus of Rio Claro, SP. Data collection ranged from April 2014 to April 2015. M. cerberus styx showed a more irregular profile of productivity along the four seasons, presenting in general the greatest values on summer and the lowest values on winter. M. cassununga, on the other hand, seemed to have a more stable rhythm of productivity, with less discrepancy between seasons, demonstrating a better performance concerning cold seasons, with the greatest productivity values on spring and the lowest values on fall. Both species showed a similar pattern of immature development with the shortest period corresponding to summer and the longest period corresponding to winter.Estudo comparativo do desenvolvimento colonial de Mischocyttarus cassununga Von Ihering e Mischocyttarus cerberus styx Richards (Hymenoptera, Vespidae, Mischocyttarini)Resumo. Mischocyttarus é um gênero de vespas eussociais pertencentes à subfamília Polistinae. Elas constroem ninhos sem envelopes, tornando-os mais facilmente observáveis e favorecendo o acompanhamento do crescimento do ninho, permitindo a observação de oviposição, desenvolvimento dos ovos, larvas e pupas, assim como a adição de novas células ao ninho e interações entre adultos. Mischocyttarus cerberus styx Richards (Hymenoptera, Vespidae, Mischocyttarini) e Mischocyttarus cassununga Von Ihering (Hymenoptera, Vespidae, Mischocyttarini) são representantes do gênero e tribo que ocorrem apenas nas américas, ocorrendo concomitantemente no município de Rio Claro (SP). O presente trabalho objetivou o acompanhamento do desenvolvimento colonial para elaborar uma abordagem comparativa de fatores que interagem com o ciclo colonial, a fim de verificar se as espécies apresentam perfil similar ou diverso entre si. Quatro locais foram escolhidos para representar a amostragem no campus da Universidade Estadual Paulista de Rio Claro, SP. O período de coleta de dados abrangeu abril de 2014 até abril de 2015, com os mapeamentos das colônias selecionadas na frequência de três vezes por semana, através do auxílio de escadas de diferentes alturas. M. cerberus apresentou um perfil mais irregular de produtividade conforme as estações, apresentando geralmente valores maiores no verão e os menores no inverno. M. cassununga por outro lado, apresentou um ritmo de produtividade mais estável, com menor discrepância entre as estações e melhor desempenho em períodos frios. Ambas as espécies demonstraram padrão similar no desenvolvimento de imaturos, sendo mais rápido no verão e mais longo no inverno.