Abstract
Athalia japonica (Hymenoptera: Tenthredinidae) showed an intermediate type of photperiodic response curve for diapause induction, when stationary photoperiods were employed. Photoperiods ranging between LD 13:11 and 14:10 stimulated continuous development. Even under these photoperiods, however, more than one third of the individuals entered diapause at 20°C and 25°C. also, when field grown larvae which were expected to enter diapause were brought into the laboratory in October, many emerged instead of entering diapause. Therefore, the possibility that A. japonica uses changing photoperiod as a cue for a developmental program was examined. Insects exposed to LD 15:9, which usually induces 100% diapause, for the first 4 days, were transferred to LD 12:12, which also usually induces 100% diapause. They were kept under LD 12:12 till cocoon formation, at which time they were transferred to LD 16:8. This transfer resulted in the lowest rate of diapause ever observed in the laboratory. The transfer, however, had to be made early during the larval stage to avert diapause, and the effect gradually decreased with later transfer. Transfer in the reverse direction was not effective at all.
