Overview of Caste Differentiation in the Polistinae, Emphasizing the Neotropical Swarm-Founding Polistinae (Hymenoptera, Vespidae, Epiponini)

Abstract

Social insects attract special attention due to their complex social interaction among individuals and their capability of forming extremely well-organized societies. In this context, social wasps represent an important group in evolutionary studies of sociality in Hymenoptera, as every step of social organization is observed, permitting the development of evolutionary scenarios which may explain the social behavior in Hymenoptera. Perhaps the main feature of social insects is the division into castes, and the higher the dimorphism between castes, the higher the level of sociality. In fact, in some groups regarded as highly eusocial such as honeybees, termites, some ants and the vespines, caste differences are extremely pronounced and the control of sociality is exercised mostly by the queens. However, in the Polistinae, some groups are regarded as basal eusocial and caste differences are absent. Such a pattern is found in Polistini, Ropalidini (some Ropalidia, Parapolybia and Belonogaster) and Mischocyrarini; in these tribes, social organization is maintained through agonistic interactions based on a hierarchy rank. Perhaps the most enigmatic situation is found in the highly eusocial swarm-founding Epiponini, in which caste systems range from species with no detectable dimorphism to species with conspicuous morphological differences. Unlike honeybees and vespines, the society of the Epiponini is characterized by a "conspiracy of workers" and the queens do not play an important role in the control of sociality. Moreover, the Epiponini society is polygynic, while the other highly eusocial insects are monogynic, and the workers control the queen demography in a process known as cyclical oligogyny. The aim of this review is to discuss the main aspects related to the caste system in social wasps with special attention to the Neotropical swarm-founding Polistinae. We provide substantial data regarding the caste system in social wasps; however, the mechanisms which led to caste differences in wasps are not well known and represent an important subject for future studies.