马尾松毛虫的光周期反应

马尾松毛虫Dendrolimus punctatus Walker和油松毛虫 Dendrolimus tabulaeformisTsai et Liu都属于长日照型昆虫。它们的光周期反应却存在着明显的差开。马尾松毛虫初龄幼虫对光照时数虽然敏感，可是只有在整个幼虫期都处在短光照周期条件下才能维持幼虫的滞育。 而且， 幼虫的滞育强度明显较弱，解除滞育所要求的条件也不如油松毛虫严格。在较高温度条件下，幼虫的滞育更不稳定，一般仅表现为生长的短暂停滞和幼虫历期的相对延长。温度和光周期还可影响到幼虫的存活和性比。马尾松毛虫幼虫呈典型的浅滞育现象。正是由于这一特性，在环境条件的影响下，长江沿岸省份不同年份马尾松毛虫二、三代分化的比例才有较大的波动，这直接关系着当地的种群动态，也是当年当地高虫口区二代虫能否成灾的关键。

PHOTOPERIODICAL REACTION OF THE PINE CATERPILLARDENDROLIMUS PUNCTATUS (WALKER)

EN ZHI-ZHONG;WEN XIAO-SUI(Forest protection station, Province Jiangxi, Nanchang 330006)Dendrolimus punctatus walker, just like D. tabulaeformis, belongs to long-daytype insect. The photoperiodic variation is the most important factor to determinethe number of generations per year. The larvae of D. punctatus show typical oligopause, its diapause could be easily terminated in less strict conditions, especially inhigher temperature. The results of our experiment also demonstrate that the larvaeof D. punctatus the sensitive reaction to the duration of daylight received in thefirst instar. When larvae in early stadia were reared in the short-day conditiorn,their growth and development usually show both temporary delay in the later instarand relative prolongation of whole larval stage. The larvae can only maintain theirdiapause in condition that the whole larval stage is under short-day photoperiodand optimal lower temperature.The oligopause type plays a key role in the differentiation of the life cycle inearly autumn. The number of generations, especially the ratio between the secondand 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.'