Effect of the endoparasitoid Campoletis chlorideae on phenoloxidase activity in Helicoverpa armigera hemolymph

Endoparasitoid wasps can develop inside permissive host due to their abilit y to overcome or to evade the host's cellular and Immoral immune response. Oviposition of Campoletis chlorideae (Hymenoptera: Ichneumonidae) in larvae of Helicoverpa armigera (Lepidoptera) was accompanied by inhibition of phe noloxidase (PO) activity and melanization reaction in host hemolymph in vit ro. PO activity in host plasma was decreased about 83% 48 h post parasitiza tion. A similar result was found when the host insect was injected with 0.5 wasp equivalent calyx fluid. This indicated that the calyx fluid was conce rned with suppression of PO activity after parasitization. Furthermore, the prophenoloxidase (proPO) in host haemocytes could be activated by bovine t rypsin in unparasitized insects, while it could not be activated in parasit ized or calyx fluid-injected host. The results suggested that inhibition of PO activity by parasitization was related to the calyx fluid of Campoletis chlorideae, and the components of calyx fluid (eg. polydnaviruses) perhaps suppressed the expression of proPO in hemolymph or accelerate the degradat ion of proPO.