Abstract: To study the effects of photoperiod and temperature on the diapause induction in the beet webworm Loxostege sticticalis, the interactive effects of temperature (18, 22, 26 and 30℃) and photoperiod (L8∶D16, L10∶D14, L12∶D12, L14∶D10 and L16∶D8) on diapause induction in this moth were investigated by artificial induction method in the laboratory. The photoperiod played the key role in diapause induction in mature larvae, followed by temperature and their interaction. Photoperiod response in L. sticticalis showed that it is a typical longday species with a critical day length of 13.97, 14.48, 13.92 and 12.88 h at 18, 22, 26 and 30℃ respectively. The day length of 12 h resulted in the highest diapause rate at all the experimental temperatures. The larvae of 11 to 17 days after hatching (about in the 5th instar) were most sensitive to the photoperiod, suggesting that the 5th instar is the most sensitive stage of diapause induction. However, the short daylight received by the 4th instar larvae was also important for the increase of their diapause rate, which can be increased from 40.0% to 90.0%.

Key words: Loxostege sticticalis, diapause, photoperiod, temperature, sensitive stage