小菜蛾主要寄生性天敌——菜蛾绒茧蜂与菜蛾啮小蜂间的相互作用

在28℃下，以小菜蛾3龄幼虫作寄主，研究了菜蛾绒茧蜂与菜蛾啮小蜂间的相互关系．当寄主供2种蜂同时产卵寄生时，与只供1种蜂时相比。绒茧蜂的寄生率无显著变化，而啮小蜂的寄生率则显著下降；2种蜂的合计寄生率与任一种蜂单独存在时相比无显著差异．当寄主先供绒茧蜂寄生，再供啮小蜂寄生时，绒茧蜂的成功寄生率不受影响，而啮小蜂的寄生率仅为8％～13％；啮小蜂能寄生在寄主体内的绒茧蜂高龄幼虫．绒茧蜂能寄生已被啮小蜂寄生的寄主幼虫，其子代部分个体能正常发育至成虫羽化．当已被绒茧蜂寄生和未被寄生的寄主同时存在时，啮小蜂主要寄生未被寄生的寄主．表明绒茧蜂具有竞争优势。但这种优势可因啮小蜂的寄生而被削弱．

Interspecific interactions between Cotesia plutellae and Oomyzus sokolowskii, two major parasitoids of diamondback moth, Plutella xylostella

The interspecific interactions between Cotesia plutellae (Kurdjumov) (Hym.: Braconidae) and Oomyzus sokolowskii (Kurdjumov) (Hym.: Eulophidae) were investigated at 28 degrees C in laboratory, by exposing the 3rd instar larvae of diamondback moth, Plutella xylostella L. (Lep.: Plutellidae) to two parasitoids concurrently, or to either species alone, and by exposing the host larvae already exposed to one species to another species. Compared with those exposures of host larvae to either one species at a time, the parasitism rates by C. plutellae were not reduced by the presence of O. sokolowskii, but the rates of parasitism by O. sokolowskii were significantly reduced by the presence of C. plutellae, when the host larvae were exposed to the two species of parasitoid concurrently. No significant differences were found between the parasitism rates done by the two species together, and those done by either one of the two species alone. When host larvae were exposed to O. sokolowskii after exposure to C. plutellae, the successful parasitism rates by C. plutellae were unaffected, while the parasitism rates by O. sokolowskii were only 8-13%. However, O. sokolowskii could parasitize the old larvae of C. plutellae developed inside host larvae. Cotesia plutellae could parasitize the host larvae parasitized previously by O. sokolowskii, and some individuals of C. plutellae in these multiparasitized hosts could develop normally and survive to adult emergence. When O. sokolowskii wasps were exposed to healthy host larvae and host larvae parasitized by C. plutellae, they preferred to parasitize the healthy ones. These results suggest that C. plutellae is the stronger competitor, but its competition capacity will be reduced by the parasitism by O. sokolowskii.