寄主龄期对菜蛾绒茧蜂生物学特性的影响

观察了小菜蛾(Plutella xylostella)被寄生时的龄期对菜蛾绒茧蜂(Cotesia plutellae)发育历期、结茧率及羽化雌蜂寄生能力的影响.结果发现：寄生于3龄小菜蛾幼虫的菜蛾绒茧蜂其卵—幼虫期的发育较寄生于2龄或4龄个体的要快，结茧率及羽化后雌蜂寄生能力要高，但寄生不同龄期寄主个体间的成蜂羽化率没有差异，表明小菜蛾3龄幼虫较2、4龄幼虫对菜蛾绒茧蜂的适合性要高.不同龄期被寄生的小菜蛾幼虫均有部分个体在寄生蜂幼虫成熟啮出前死亡，这种死亡在2龄、3龄时被寄生的个体中主要发生在幼虫期，而4龄幼虫被寄生的个体死亡发生期则逐渐向蛹期转移，4龄第三天被寄生的小菜蛾蛹期死亡率达62.5%，表明小菜蛾4龄幼虫对菜蛾绒茧蜂的适合性随年龄增加迅速下降.文中还讨论了寄主龄期适合性与该蜂产卵选择性的关系.

The effect of host age on biological characteristics of Cotesia plutellae

The effects of larval instars and ages of Plutellae xylostella at initial parasitization on developmental time, rate of cocoon formation, and parasitic capacity of resultant female wasp of Cotesia plutellae , were observed. The results showed that the development of egg and larva of parasitoid initially parasitizing in the 3rd instar larva was faster than development of those initially parasitizing in the 2 nd and the 4 th instars larvae. The rate of cocoon formation and parasitic capacity of resultant female wasps were also higher in former, indicating that the 3 rd instar larva of P. xylostella was more suitable than the 2 nd and the 4 th instars larvae for C. plutellae , though host age at parasitization had no effect on the emergence rate of parasitoids. In all host instars and ages tested, there were some parasitized individuals that died before the parasitoid larva matured and ate out of the host. For host larvae initially parasitized at the 2 nd and the 3 rd instars, these deaths occurred mainly during larval development; for those larvae initially parasitized at the 4 th instar, many deaths occurred during pupal development. When host larvae were initially parasitized at the 3 rd day of the 4 th instar, 62.5% of parasitized larvae died at the pupal stage. The relationship between suitability of host age and oviposition preference of parasitoid was also discussed.