Parasitism of Cotesia spp. Enhances Susceptibility of Plutella xylostella to Other Pathogens

Two endoparasitoids, Cotesia plutellae and C. glomerata, parasitize the diamondback moth, Plutella xylostella, and induce significant host immunosuppression. This study analyzed the susceptibility changes of the parasitized P. xylostella against other pathogens using an entomopathogenic bacterium, Xenorhabdus nematophila (Xn), and a viral pathogen, Autographa californica nucleopolyhedrosis virus (AcNPV). The P. xylostella parasitized by either C. plutellae or C. glomerata exhibited higher susceptibilities to both microbial pathogens than the nonpara-sitized. To determine the parasitism factors inducing the enhanced susceptibility, three polydnaviral genes so far successfully cloned were selected from C. plutellae bracovirus (CpBV). CpBV-lectin and CpBV15 α/β were inserted into AcNPV under a CpBV promote and analyzed in their pathogenicities against P. xylostella larvae. Two AcNPVs recombined with CpBV15α/β were more potent than the control AcNPV recombined with an enhanced green fluorescent protein gene or the AcNPV recombined with CpBV-lectin. These results suggest that the wasp parasitization enhances other pathogen susceptibilities by inducing host immunosuppression, in which the symbiotic polydnavirus can play significant role in the enhanced susceptibility.