Effect of the endoparasitoidCampoletis chlorideae on phenoloxidase activity inHelicoverpa armigera hemolymph

Abstract

Endoparasitoid wasps can develop inside permissive host due to their ability to overcome or to evade the host’s cellular and humoral immune response. Oviposition ofCampoletis chlorideae (Hymenoptera: Ichneumonidae) in larvae ofHelicoverpa armigera (Lepidoptera) was accompanied by inhibition of phenoloxidase (PO) activity and melanization reaction in host hemolymphin vitro. PO activity in host plasma was decreased about 83% 48 h post parasitization. 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 concerned with suppression of PO activity after parasitization. Furthermore, the prophenoloxidase (proPO) in host haemocytes could be activated by bovine trypsin in unparasitized insects, while it could not be activated in parasitized or calyx fluid-injected host. The results suggested that inhibition of PO activity by parasitization was related to the calyx fluid ofCampoletis chlorideae, and the components of calyx fluid (eg. polydnaviruses) perhaps suppressed the expression of proPO in hemolymph or accelerate the degradation of proPO.