Caste asymmetries in the neotropical Swarm-founding wasp polybia (Trychothorax) ignobilis (Hymenoptera, Vespidae, Epiponini)

Abstract

Epiponini wasps are dominant in Neotropical regions and represent, in several ways, exceptions for general theories regarding social insects. They are highly eusocial and most species build large and complex nests. These wasps form large populations, and colony reproductive fission occurs by swarming. On the other hand, differently from otherhighlysocial insects, in several species morphological differences among castes are slight or absent, suggesting that caste determination in the Epiponini differs from better known systems. In fact, the mechanisms that lead to caste differentiation in this tribe still remain obscure. The aim of this study is to investigate the pattern of caste differentiation during the colonial cycle of the Neotropical Epiponini wasp Polybia (T.) ignobilis. Measurements were taken from 13 morphometric variables regarding the head, metassoma, messosoma, and wing. Ovarian development, relative age, and fat bodies were also examined. Four patterns of ovarian development were found and varied from filamentous ovarioles with no visible oocytes to well-developeded ovaries with mature oocytes. ANOVA showed that queens were significantly larger than workers in all colony phases, and also showed some significant differences between workers and intermediates in some body parts. However, multivariate statistics revealed that intermediates are in fact morphologically similar to workers, whereas queens were identified as a different group composed of larger individuals. Caste differentiation varied according to the colony cycle: the morphological differences between queens and workers tend to increase with colony maturity.