Abstract
We examined the sensitive stage to summer diapause induction of Chrysocharis pubicornis. Individuals of different ages were transferred from diapause-preventing (15°C–12L : 12D) to diapause-inducing conditions (25°C–16L : 8D) throughout the 22-day egg-larval period. Transferring 15-day-old (third instar larvae about to complete feeding) or younger individuals resulted in more than 60% diapause; however, less than 25% of larvae entered diapause when transferred at 18 days (full-grown, resting third instar) or older. This suggests that sensitivity is high in younger instars, but decreases in the last instar. Moreover, individuals transferred at 18 days emerged 15 days earlier than control individuals continuously reared at 15°C–12L : 12D. We also examined the effects of cooling treatment duration on diapause termination by exposing diapausing larvae to 15°C–12L : 12D for increasing periods, followed by transfer to 25°C–16L : 8D. The percentage of diapause termination and the time to adult emergence increased with the cooling period, and it took between 12 and 16 days for 50% of individuals to complete diapause. The diapause termination rate after 20-day cooling was similar to that under continuous cooling (<90%), but the time to emergence was significantly shortened by 15 days. The implications of our findings in an eventual biocontrol program are discussed.
