Abstract: Dendrolimus punctatus walker, just like D. Tabulaeforrnis, belongs to long-day type insect. The photoperiodic variation is the most important factor to determine the number of generations per year. The larvae of D. punctatus show typical oligopause, its diapause could be easily terminated in less strict conditions, especially in higher temperature. The results of our experiment also demonstrate that the larvae of D. punctatus the sensitive reaction to the duration of daylight received in the first instar. When larvae in early stadia were reared in the short-day condition, their growth and development usually show both temporary delay in the later instar and relative prolongation of whole larval stage. The larvae can only maintain their diapause in condition that the whole larval stage is under short-day photoperiod and optimal lower temperature. The oligopause type plays a key role in the differentiation of the life cycle in early autumn. The number of generations, especially the ratio between the second and third generations varies with the weather each year near 30°N region in China. Obviously, the fluctuation of ratio affects the population dynamics next year and thehigher ratio of third generation will cause more serious damage in forests with abundant pests.

Key words: Dcndrolimus punctatus——photoperiodic reaction——oligopause