none Ascogaster reticulatus Watanabe is an egg-larval parasitoid of the smaller tea tortrix moth, Adoxophyes sp. Diel patterns of adult emergence and mating in this parasitoid were observed in the laboratory, and the effect of adult age on the mating was also analyzed. Most of the adult parasitoids emerged within a few hours after light-on, and the emergence peak of the male was earlier than that of the female by one day. High mating activity of these parasitoids was observed in the latter half of a light period when the walking activity of both sexes was also high. Premating period of males was longer than females. The combination of 3-day-old males and 1- to 2-day-old females was most appropriate for mating. High mating rate was obtained from the density of up to 5 pairs in a container (ca. 2 l). In addition to the conditions for mating, mating behavior is briefly described.