半闭弯尾姬蜂的寄主选择性及寄生对寄主发育和取食的影响

在24℃下研究了半闭弯尾姬蜂寄生对寄主幼虫龄期的选择性及对寄主生长发育、取食量的影响。结果表明，该蜂能寄生小菜蛾2-4龄的幼虫，但当2-4龄幼虫同时存在时，偏爱寄生2、3龄幼虫，对2、3、4龄幼虫的选择系数分别为0．37、0．44、0．19。该蜂对4龄幼虫的寄生能力随寄主日龄增大而下降。2-4龄小菜蛾幼虫被寄生后，总发育历期与预蛹期都比未被寄生的显著延长。当小菜蛾幼虫在2龄初被寄生后，总取食量比未被寄生的显著减少；但当幼虫在3、4龄初被寄生后，各龄的取食量与未被寄生的差异不显著。

Parasitism Preference of Diadegma semiclausum to Host Age and the Effect of Parasitism on the Development and Food Consumption of the Host Plutella xylostella

The parasitism preference of Diadegma semiclausum Helln to different larval instars of diamondback moth (DBM), Plutella xylostella (Linnaeus) and four development ages of its 4th instar, and the effect of parasitism on the development and food consumption of DBM were studied in the laboratory at 24. The results showed that D. semiclausum could parasitize 2-4 instars of DBM larvae, but preferred to 2nd and 3rd instars when the 2nd, 3rd and 4th instars of host larvae were exposed simultaneously to this parasite. The preference indexes to the 2nd, 3rd and 4th instars were 0.37, 0.44 and 0.19, respectively. The parasitic ability of D. semiclausum to the 4th instar DBM decreased with the increase of developmental age in this instar. The duration of prepupal and immature stages of the parasitized DBM larvae prolonged significantly. The host larvae were parasitized initially at the 2nd instar consumed less food than those unparasitized. However, there were no significant difference in the total food consumption between the larvae parasitized initially at the 3rd or 4th instar and those unparasitized.