Precopulatory Behavior of Males and Perception of a Potential Male Pheromone in Spruce Budworm, Choristoneura fumiferana1

Precopulatory behavior of male spruce budworms was examined by direct observation and sequential photography. Groups of males isolated from females exhibited sexual behavior and engaged in homosexual copulations throughout the day. When both sexes were together, heterosexual matings occurred even in morning hours when females were not calling. In the presence of calling females the incidence of heterosexual matings increased considerably. We conclude that males have an intrinsic basal level of sexual activity which is related neither to the presence of female nor her pheromone. A role of the sex pheromone is to enhance this basal level of male sexual activity. The behavior of sexually excited males in homo- or heterosexual mating attempts was similar in all respects. A sexually excited male always spread its abdominal hairs before mating with a female or a male. Extracts of male abdominal tips or whole wings or the airborne volatiles from males gave EAG responses in both sexes. SEM pictures revealed the existence of structures on the wings and the abdominal tip of males which may be scent glands.