Functional morphology of the ovipositor in Megarhyssa atrata (Hymenoptera,Ichneumonidae) and its penetration into wood

Megarhyssa atrata (Pimplinae) is the largest species known amongst Hymenopt era. In its natural habitat, North America, it is a strict parasitoid of Tr emex columba (Hymenoptera, Symphyta, Siricidae). The parasite infests xylop hagous host larvae buried in wood. The present work describes the complex m ovements of the ovipositor during oviposition and its flexibility ensuring the positioning of the stylus at the site of boring. These movements are ma de possible by the unfolding of the intersegmentary membranes (equipped wit h a secretory internal surface) and by the full rotation of abdominal segme nts 8 and 9. During this rotation, the stylus of the ovipositor pushes and extends the membranes completely which, as a result, form a translucent dis c measuring 2 cm in diameter. The entry of the stylus into wood is helped b y another secretion produced at the tip of the valvulae. This lytic secreti on destroys wood fibers. With this set of adaptations, the hymenopteran can bore into a thickness of hard wood and reach its host larvae at a depth of 14 cm.