Effects of photoperiod and temperature on diapause induction and termination in the swallowtail, Sericinus montelus

Sericinus montelus overwinters as diapausing pupae. In the present study, the effects of photoperiod and temperature on diapause induction and termination of diapause are investigated. The results obtained demonstrate that high temperature can reverse the effect of short day-lengths on diapause induction. Under an LD 12 : 12 h photoperiod, all pupae enter diapause at 15, 20 and 25 degrees C, whereas all pupae develop without diapause at 35 degrees C. No pupae enter diapause under an LD 14 : 10 h photoperiod when the temperature is above 20 degrees C. Photoperiodic response curves obtained at 25 and 30 degrees C indicate that S. montelus is a long-day species and the critical day-length is approximately 13 h at 25 degrees C. At 25 degrees C, the duration of diapause is shortest when the diapausing pupae are maintained under an LD 16 : 8 h photoperiod and increases under LD 14 : 10 h and LD 12 : 12 h photoperiods. Under an LD 16 : 8 h photoperiod, the duration of diapause is shortest when the diapausing pupae are maintained at 25 degrees C, followed by 20 and 30 degrees C, and then at 15 degrees C. These results suggest that a moderate temperature favours diapause development under a diapause-averting photoperiod in this species. The duration of diapause induced by an LD 12 : 12 h photoperiod is significantly longer at 25 degrees C than those at 15, 20 and 30 degrees C, and is shortest at 15 degrees C. At 25 degrees C, the duration of diapause induced by LD 6 : 18, LD 12 : 12 and LD 13 : 11 h photoperiods is similar and longer than 90 days. Thus, the diapause-inducing conditions may affect diapause intensity and a photoperiod close to the critical day-length has significant influence on diapause intensity in S. montelus.