Parasitic effects on host Plutella xylostella testes by two endoparasitoids
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Key Words： testes, endoparsitoid, polydnavirus, Plutella xylostella, instar
Abstract： The effects of the endoparasitoids Cotesia vestalis(Haliday) or Diadegma semiclausum Hellén on the germ cell and testicular growth of their host, Plutella xylostella(L.), were studied. C. vestalis and D. semiclausum carry two types of polydnaviruses. The results show that both C. vestalis bracovirus and D. semiclausum ichnovirus can inhibit host spermatogenesis and spermiogenesis; there were no, or only a few, sperm bundles in parasitized host testes. Inhibition of spermiogenesis was almost complete in hosts parasitized during early stages of development but was less severe in those parasitized at the 4th (final) stadium. Testicular growth of P. xylostella was also inhibited by parasitization; younger hosts developed smaller testes than those parasitized at the 4th stadium. The degree of castration therefore depends on the age at which the host is parasitized. C. vestalis had a significantly stronger suppressive effect on host germ cell and testicular growth than D. semiclausum.