Abstract

Scanning and transmission electron microscopy techniques were used to perform this first investigation of the ovipositor of Choristoneura fumiferana. The female spruce budworm has four types of trichoid sensilla on its ovipositor. A unique and rare type of sensillum is described. This Type II sensillum is multiporous and also has a single pore at the tip. The other sensillar types found were: Type I and III sensilla, which are short and long multiporous hairs respectively, and Type IV sensilla which are long, aporous hairs. Type I and III hairs are probably olfactory, while Type IV hairs are probably mechanosensory. Type II hairs are innervated by 4 dendrites. Physiological responses were obtained from only these Type II sensilla using the tip recording method. Behavioural studies have shown that mated insects are encouraged to oviposit in the presence of host waxes whereas virgins are not. The response of Type II hairs to waxes in solution from their most preferred host, white spruce (Picea glauca), revealed no differences between unmated and mated insects. Mated and unmated females' sensilla responded differently to common polar nutrients. Results from this study suggest that mated females may be using polar compounds rather than the surface waxes to locate potential hosts.