Abdominal modifications occurring in wasp mimics of the Ctenuchine-Euchromiine clade (lepidoptera: arctiidae)

Abstract

Members of the arctiine moth tribes Ctenuchini and Euchromiini exhibit extreme morphologies including the evolution of convincing wasp mimicry. The lepidopteran abdomen is constricted to produce the visual effect of a hymenopteran petiole (petiole mimic). Many of these species also possess an abdominal 'ventral valve' that has been ascribed both a defensive and a courtship function. We examined 85 species (45 genera) to determine the structural variation and distribution of these unique morphologies. Width-length ratios of modified and unmodified segments were generated from 52 species to describe the abdominal constriction in petiole mimics and unmodified abdomen. Here, we provide the first detailed descriptions and illustrations of the morphologies of petiole mimics and ventral valves. Two independent derivations of petiole mimics occur in this clade. Similarly, not all ventral valves are homologous. We propose the phrase 'subabdominal pouch' to replace 'ventral valve' because it more accurately describes these morphological structures. Petiole mimics may involve modification of either sternite II (SII) or III, but only SIII petiole mimics lack subabdominal pouches. This result suggests that the presence of one morphological innovation (petiole mimic) limits the possession of the other (androconial type).