Abstract:

The venom of pupal endoparasitoid wasp, Diadromus collaris (Hymenoptera: Ichneumonidae) and its immunosuppression effects on the pupae of host Plutella xylostella (Lepidoptera: Plutellidae) were preliminarily studied. The total number of hemocytes and the numbers of two types of hemocytes (plasmatocytes and granular cells) increased in the hemolymph of parasitized host pupae as compared with those in non-parasitized hosts. The morphology and behavior of plasmatocytes and granular cells in the hemolymph of parasitized host pupae were also changed. The adhesion and spreading behavior were inhibited in plasmatocytes and granular cells in one day after oviposition. The spreading behavior in plasmatocytes from the host larvae was also suppressed whereas that of granular cells was not significantly affected in the in vitro culture experiments. Isolated crude venom also caused the death and break of plasmatocytes and granular cells. The in vitro culture experiments also indicated that the venom of this pupal endoparasitoid inhibited the phenoloxidase activity of hemolymph of host larvae in a certain extent, especially when the reaction time is up to 40, 60 and 80 minutes. The venom SDS-PAGE showed that nine protein bands were present, ranging from 9 to 50.2 kD, including 50.2, 30.5, 28.2, 25.1 and 12.6 kD, which were similar to proteins acted as the inhibitors for host development and immunity in other parasitoidhost systems. The results above demonstrated that venom of D. collaris could impair cell and humor-mediated immune responses of the host.
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Key words: Diadromus collaris, Plutella xylostella, venom, immunosuppression, parasitizationassociated factors, hemocyte, phenoloxidase activity