菜蛾绒茧蜂的寄主选择性及寄生对寄主发育和取食的影响

研究了菜蛾绒茧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，该蜂能寄生小菜蛾各个龄期的幼虫，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、０．３９、０．２４。该蜂对４龄幼虫的寄生能力随寄主日龄增大而急剧下降，对进入４龄并发育至该龄期４０％时间以上的幼虫不能寄生。产卵寄生的雌蜂比例也随４龄幼虫日龄增大而急剧下降。小菜蛾幼虫被寄主后

PARASITISM PREFERENCE OF COTESIA PLUTELLAE TO HOST AGE AND THE EFFECT OF PARASITISM ON THE DEVELOPMENT AND FOOD CONSUMPTION OF THE HOST PLUTELLA XYLOSTELLA

The parasitism preference of Cotesia plutellae Kurdjumov 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. The results showed that C. plutellae could parasitize all the four instars of DBM larvae, but prefered 2nd and 3rd instars when the 2nd, 3rd and 4th instars of host larvae were exposed simutaniously to this parasite. The preference indexes to the 2nd, 3rd and 4th instars were 0. 37, 0. 39 and 0. 24, respectively. The parasitic ability of C. plutellae to 4th instar DBM decreased rapidly with the increase of developmental age in this instar, as the larvae had gone over 40% of the instar duration, no more parasitism occurred. The parasitized DBM larvae had prolonged their 4th instar duration obviously, and the later the larva had been parasitized, the longer this extended duration became. The parasitized larvae had consumed more food than the healthy ones, but the former could not pupate. Methods for determining the parasitization of C. plutellae in the field were also discussed.