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 s canning and transmission electron microscopy. Characteristic peg-like sensi lla with a cuticular ring at the base are found at the tip of the ventral v alves, where they occur in a characteristic arrangement of triplets. The un usual basal structure probably protects the sensilla against damage during movement through the substrate and piercing of the host cuticle. These sens illa are each innervated by six dendrites, some of which have lamellated ti ps, generally considered to be characteristic of thermosensitivity. It is s uggested that the remaining dendrites are gustatory, and as such probably r espond to factors present in host haemolymph. A second type of peg-like sen sillum 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 t he cuticle. These occur along the length of the ovipositor shaft and ultras tructural studies reveal the pegs to be innervated by a single mechanosensi tive dendrite, probably monitoring the movement of the ovipositor through t he substrate. (C) 1998 Elsevier Science Ltd. All rights reserved.