none Mating behavior of the egg-larval parasitoid Ascogaster reticulatus WATANABE was observed in the laboratory. The sequence of mating behavior of the male parasitoid was summarized as follows: random walking, antennal searching, orientation, pursuit, approach, antennal contact, mounting, and copulation. A hexane extract from the female body, drawn across the bottom of the petri dish, elicited male antennal searching while walking along the line. Dose-response curve of the behavior had a peak between concentrations of 10-3 and 10-2 female equivalent per line. In another experiment, male parasitoids actively searched the tea leaves on which females had walked. These facts indicated that the male responded to a sex pheromone left by females. The sex pheromone deposited by the females seemed to activate male searching and increase the chances of mating behavior.