Morphology and functions of calyx fluid filaments in the reproductive tracts of endoparasitoid,Microplitis mediator [Hym.: Braconidae]

An Ovarian Protein Involved in Passive Avoidance of an Endoparasitoid To Evade Its Host Immune Response

Through a combination of transcriptomic and proteomic analyses, we identified 817 secreted ovarian proteins from an endoparasitoid wasp, Cotesia chilonis, of which five proteins are probably involved in passive evasion. The results of an encapsulation assay revealed that one of these passive evasion-associated proteins (Crp32B), a homologue of a 32-kDa protein (Crp32) from C. rubecula, could protect resin beads from being encapsulated by host hemocytes in a dose-dependent manner. Crp32B is transcribed in ovarian cells, nurse cells, follicular cells, and oocytes, and the protein is located throughout the ovary and on the egg surface. Moreover, Crp32B has antigenic similarity to several host components. These results indicate that C. chilonis may use molecular mimicry as a mechanism to avoid host cellular immune response.

Effects of the endoparasitoid Cotesia chilonis (Hymenoptera: Braconidae) parasitism, venom, and calyx fluid on cellular and humoral immunity of its host Chilo suppressalis (Lepidoptera: Crambidae) larvae

The larval endoparasitoid Cotesia chilonis injects venom and bracoviruses into its host Chilo suppressalis during oviposition. Here we study the effects of the polydnavirus (PDV)-carrying endoparasitoid C. chilonis (Hymenoptera: Braconidae) parasitism, venom and calyx fluid on host cellular and humoral immunity, specifically hemocyte composition, cellular spreading, encapsulation and melanization. Total hemocyte counts (THCs) were higher in parasitized larvae than in unparasitized larvae in the late stages following parasitization. While both plasmatocyte and granulocyte fractions and hemocyte mortality did not differ between parasitized and unparasitized hosts, in vitro spreading behavior of hemocytes was inhibited significantly by parasitism throughout the course of parasitoid development. C. chilonis parasitism suppressed the encapsulation response and melanization in the early stages. Venom alone did not alter cellular immune responses, including effects on THCs, mortality, hemocyte composition, cell spreading and encapsulation, but venom did inhibit humoral immunity by reducing melanization within 6h after injection. In contrast to venom, calyx fluid had a significant effect on cell spreading, encapsulation and melanization from 6h after injection. Dose-response injection studies indicated the effects of venom and calyx fluid synergized, showing a stronger and more persistent reduction in immune system responses than the effect of either injected alone.

The calyx fluid of Microplitis rufiventris parasitoid and growth of its host Spodoptera littoralis larvae

The morphology of the female reproductive system of pupal and adult stages of Microplitis rufiventris and the ultrastructure of the ovaries are described and illustrated. Two morphologically distinct types of particles of nuclear origin, i.e., polydnavirus (PDV) and a virus-like filamentous particle (VLFP) were detected in the ovarian calyx fluid of the female wasp. It is likely that these particles are injected into the host during oviposition. PDV initiated replication in the calyx of mid-aged pupae and in pharate adults and were present throughout adult life. VLFP were only seen in the calyx fluid of newly emerged adults, and therefore observed after the PDV. Feulgen and methyl-green pyronin staining revealed the presence of DNA in both types of particles. The effects of injection of Spodoptera littoralis larvae with a combination of parasitoid viruses and venom of M. rufiventris females (CxFV) were investigated and the results were compared with two control groups, i.e., larvae injected with Pringle's saline (PS) and naturally parasitized larvae. CxFV-larvae showed significant declines (P<0.05) in food consumption, weight of ejected faeces and weight gain when compared with PS-larvae. However, naturally parasitized larvae (parasitoid egg+CxFV+ovarian protein) displayed a high significance score (P<0.01) in comparison with those of PS-larvae. The approximate digestibility (AD) values of S. littoralis larvae were positively affected as early as day 2 post-treatment by either injection of CxFV or parasitization. However, a reduction in AD was observed in both PS- and CxFV-larvae on day 3-7 in comparison with naturally parasitized larvae. Other indices of food utilization were unchanged in CxFV-larvae when compared to saline treated or parasitized controls.