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抑制寄主昆虫的免疫反应是内寄生蜂存活的关键。菜蛾盘绒茧蜂Cotesia vestalis(Haliday)寄生小菜蛾Plutellaxylostella(L.)幼虫后,蜂卵如何逃避和抑制寄主的免疫攻击,尚未得到全面揭示。本文采用电镜技术系统观察了菜蛾盘绒茧蜂卵表面的超微结构。结果显示:蜂卵表面覆盖有纤维层和絮状的类病毒样纤丝(VLFs),同时携带了含多分DNA病毒粒子(PDV)的萼液。在寄生初期,包裹在蜂卵表面的纤维层和VLFs首先起到保护蜂卵不被小菜蛾血细胞包囊的被动防御作用。随后,PDV发挥主动的免疫抑制作用。通过假寄生手段,证明了菜蛾盘绒茧蜂PDV(CvBV)具有较持久的克服寄主免疫攻击的能力,是主要的免疫抑制因子。在假寄生后连续8d的观察时间内,菜蛾盘绒茧蜂的蜂卵均未被包囊。结果提示,在菜蛾盘绒茧蜂-小菜蛾寄生体系中,菜蛾盘绒茧蜂采取被动防御和主动攻击两种方式应对寄主小菜蛾的免疫攻击。
Inhibition of host immune response of insects is the key to survival of parasitoids. How egg bees evade and suppress host immune attack after parasitizing the Plutella xylostella (L.) larvae by the parasitoid Cotesia vestalis (Haliday) has not yet been fully revealed. In this paper, electron microscopy technique was used to observe the oviposition of the diamondback moth, Plutella xylostella ultrastructure. The results showed that the egg surface was covered with fibrous layers and flocculent VLFs, along with calyx fluid containing multiple DNA fragments (PDV). In the early stages of parasitism, the layers of fiber and VLFs that wrap around the egg surface of the bee first served as a passive defense against the encapsulation of the eggs of the Plutella xylostella by blood cells. Subsequently, PDV plays an active immunosuppressive role. Through pseudo-parasitic means, PDV (CvBV) of Plutella xylostella was proved to be a major immunosuppressive factor with more lasting ability to overcome host immune attack. During the observation period of 8 days after false parasitism, the bee eggs of Plutella xylostella were not encapsulated. The results suggest that in the parasitism of Plutella xylostella-Plutella xylostella, both the passive defense and the active attack on the diamondback moth, Plutella xylostella, could deal with the immune attack against the host diamondback moth, Plutella xylostella.