菜蛾盘绒茧蜂主要寄生因子导致的寄主小菜蛾幼虫脂肪体结构的变化

在不同的寄生状态下，菜蛾盘绒茧蜂Cotesia plutellae不同的寄生因子可引起寄主小菜蛾Plutella xylostella幼虫脂肪体结构发生相应的改变。显微和亚显微形态结构显示： 假寄生后多分DNA病毒和毒液对脂肪体结构的完整性没有显著影响，但细胞内脂质体变得小而密集，线粒体和内质网丰富，并有糖原积累； 正常寄生后，脂肪体结构被破坏，多数线粒体内嵴紊乱，脂质体也变得不规则，特别是当幼蜂完成在寄主体内发育时，寄主体内几乎无完整脂肪体存在。与此同时，同批未被寄生的小菜蛾幼虫发育到4龄末期时，体内脂肪体细胞发育正常，已开始向蛹期细胞形态转化，细胞内脂质体很大，细胞器数量较多、糖原积累丰富, 而且部分细胞已成为游离态细胞。由此证明，寄生蜂携带的寄生因子，如多分DNA病毒、毒液、畸形细胞和幼蜂等，均对寄主脂肪体结构的改变产生影响，但程度明显不同。

Effects of parasitism factors of the parasitoid Cotesia plutellae on fat body structure of the host Plutella xylostella larvae

Changes in the fat body structure of the host Plutella xylostella (Lepidoptera: Plutellidae) larvae induced by different parasitism factors of the parasitoid Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) in different parasitized states were observed with light microscopy and transmission electron microscopy. The results revealed that the fat body cytology of parasitized larvae was different from those of pseudo-parasitized host and non-parasitized control. The polydnavirus (PDV) and venom had no obvious effects on the fat body structure in the pseudo-parasitism condition, where the fat body maintained the integrality with normal stacks of endoplasmic reticulum and mitochondria, glycogens accumulated in some cells, and more amounts of total lipids present but smaller as compared with those of the non-parasitized host larvae. The most striking features of fat bodies in the parasitized larvae were the cytoplasmic organelles decreased and mitochondria with ill-defined cristae, and especially during the final parasitism stage (when parasitoid larvae completed their development), the fat body structure was severely destroyed. In contrast, when the non-parasitized larvae were in the final phase of the 4th instar, the fat body cells developed normally and were undergoing transformation from the larval into prepupal stage, with large lipid bodies and rich mitochondria and glycogen present,some of them existing in free cell rosettes. These results suggest that different parasitism factors, i.e. PDV, venom, teratocytes and parasitoid larvae, have different effects on the host fat bodies.