Interacting Effects of Temperature and Photoperiod on Diapause in Larvae of Monochamus alternatus (Coleoptera : Cerambycidae)

Fourth-instar, diapause and prediapause Monochamus alternatus larvae were collected from dead Pinus thunbergii trees and their developmental responses to laboratory conditions were investigated in early October. In continuous darkness, diapause was maintained at 25℃, but on incubation at 25℃ after chilling for 121-122 days at 10℃, prediapause larvae averted diapause and diapause larvae terminated diapause. Under a photoperiod of 16L-8D at 25℃, some prediapause larvae averted diapause, and diapause larvae either maintained or terminated diapause. After chilling at 10℃ under 16L-8D for 121-122 days, a high larval mortality occurred, and at 25℃ under 16L-8D, diapause was averted or terminated. When fourth instar larvae in P. thunbergii bolts were placed at 25℃ under 16L-8D in early October, they did not emerge as adults for 187 days, indicating that they could not perceive the photoperiod in the bolts. It was concluded that a low temperature of 10℃ conditioned prediapause larvae to avert diapause and diapause larvae to terminate diapause. Continuous darkness stabilized the larval response to temperature while photoperiod blurred it.