Life History of the Pupal Parasitoid Diadromus subtilicornis (Gravenhorst)(Hymenoptera : Ichneumonidae) as Influenced by Temperature, Photoperiod, and Availability of Food and Hosts

Laboratory experiments were conducted to determine life history characteristics of Diadromus subtilicornis, a pupal parasitoid of diamondback moth, using the two parasitoid strains collected from Morioka and Akashi, Japan. Developmental time from oviposition to emergence decreased with increasing temperature with either 16L : 8D or 12L : 12D. Longevity of both sexes decreased with increasing temperature. Females lived longer than males at the same temperatures and photoperiods. Females reared at 25℃ with 16L : 8D had no mature eggs at day 0. The number of mature eggs per female increased up to 5 by day 5, and then decreased after day 15 although they had no access to hosts. These results indicate that they resorb mature eggs and avert egg maturation when deprived of hosts for a long period. When given hosts and honey solution with 16L : 8D, females lived shorter and produced fewer progeny at 30℃ than at either 20℃ or 25℃. When given hosts daily only after day 20 or day 35 at 25℃ with 16L : 8D, females produced fewer progeny than females given hosts daily since adult emergence. Longevity of 35-day host-deprived females was longer than that of undeprived females and of 20-day host-deprived females, indicating extension of longevity due to reproductive suppression. Considering the plasticity of their life history, combined with their long lifespans and capacity to attack a few hosts a day for an extended period, D. subtilicornis could be used for prevention of buildup of diamondback moth populations in early summer in Japan.