Ultramorphology of the ovipositor of Venturia canescens (Gravenhorst) and possible mechanisms for oviposition

Morphology, ultrastructure and possible mechanics of the ovipositor of Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae) is described using scanning and transmission electron microscopy. The ovipositor of V. canescens consisted of three pairs of valvulae. First pair or dorsal valvulae and the second pair or ventral valvulae constituted the ovipositor shaft and the third pair formed the ovipositor sheaths. The ventral valvulae possessed five conical ridges or barbs at the distal end. The diameter of the ovipositor shaft decreased from proximal to distal end of the ovipositor shaft terminating in a very sharp tip. The dorsal valvulae possessed a blunt tip and a pre-apical notch on the dorsal surface. The dorsal and ventral valvulae collectively formed the egg canal with the help of two functional units called olistheters for the transport of eggs. A robust longitudinal ridge on ventral tip of dorsal valvulae that tappered on both ends is called sperone. The ovipositor sheaths covered the ovipositor shaft completely when at rest. Groups of ctenidia covered the internal surface of the sheaths throughout its length. The surfaces of all the valvulae were covered with sense organs. The knowledge of these structures helps understand their functions in host location, discrimination and oviposition behavior. (C) 2012 Friends Science Publishers