Morphology and ultrastructure of sense organs on the ovipositor of Trybliographa rapae, a parasitoid of the cabbage root fly.

The ovipositor of the parasitoid wasp Trybliographa rapae was examined by scanning and transmission electron microscopy. Characteristic peg-like sensilla with a cuticular ring at the base are found at the tip of the ventral valves, where they occur in a characteristic arrangement of triplets. The unusual basal structure probably protects the sensilla against damage during movement through the substrate and piercing of the host cuticle. These sensilla are each innervated by six dendrites, some of which have lamellated tips, generally considered to be characteristic of thermosensitivity. It is suggested that the remaining dendrites are gustatory, and as such probably respond to factors present in host haemolymph. A second type of peg-like sensillum is found on both the dorsal and the ventral valves. These are set in deep pits so that only the tip of the peg protrudes above the surface of the cuticle. These occur along the length of the ovipositor shaft and ultrastructural studies reveal the pegs to be innervated by a single mechanosensitive dendrite, probably monitoring the movement of the ovipositor through the substrate.