Abstract:

We had found that the parasitization by Cotesia vestalis and Diadegma semiclausum inhibited their host larval spermatogenesis seriously. This study intends to compare the testicular growth and the formation of sperm bundles in Plutella xylostella parasitized by the above two endoparasitoids, so as to make clear of the regulation capabilities of parasite factors on host reproductive system. By using the methods of superparasitism and pseudoparastism, the changes in testicular volume and morphology of spermatogenic cells and sperm bundles during the host larval spermatogenesis and spermiogenesis parasitized separately by the two endoparasitoids were compared. The results showed that parasitization by the two endoparasitoids both resulted in a reduction in the number of sperm bundles, and the spermatogenesis and spermiogenesis were retarded too. The abnormal testis structure or deformed sperm bundles were observed in P. xylostella parasitized by the two wasps. The degree of testis degeneration was more severe in P. xylostella parasitized by C. vestalis than that by D. semiclausum. Superparasitization induced more pronounced parasitic castration when compared with a single parasitism. After superparasitization separately by C. vestalis and D. semiclausum, the host testicular volume was 0.005 mm³ and 0.008 mm³, only 33.1% and 33.6% of their singly parasitized host testicular volume, respectively. Pseudoparasitization also resulted in testis degeneration, and the degree of degeneration was almost as severe as in the naturally parasitized hosts, suggesting that polydnavirus and venom are involved heavily in host castration. It is so inferred that the mechanisms adopted by the bracovirus and ichnovirus in host castration may be different.

Key words: Cotesia vestalis, Diadegma semiclausum, Plutella xylostella, testis, sperm bundle, parasitization, pseudoparasitization, polydnavirus