From hair pin to safety pin: evolution of the ovipositor apparatus in Orussidae (Insecta: Hymenoptera)

Abstract

Orussidae, a small family of parasitoid wasps targeting woodboring insect larvae, are characterized by having the ovipositor apparatus invaginated in the body and operated by a mechanism unique among Hymenoptera. The first and second valvulae when not in use lie in an invaginated ovipositor sack extending forward throughout the abdomen and thorax. During oviposition, the valvulae are extended and retracted by a combination of small median apodemes on the anterior margin of abdominal sterna 3–7 gripping and releasing the ovipositor, and rocking motions of the sterna. Females representing different genera of Orussidae were examined by dissection and SEM, revealing overall similarity of the ovipositor system and its inferred mode of operation in a larger sample across the family, but also variation between genera in the way the ovipositor is accommodated. This includes differences in the prophragma, profurca and the internal part of the mesonotum where the anterior loop of the ovipositor is stored, and the shape of the loop itself which occurs in two configurations: simple hair pin-like bend or whorled, safety pin-like. The former is putatively the plesiomorphic condition in Orussidae, the latter possibly having evolved more than once to accommodate a longer ovipositor. Selected features in the ovipositor apparatus are mapped and discussed in the context of recent phylogenetic hypotheses for the family.