| The effectiveness of endoparasitoid Tetrastichus brontispae Ferriere,belonging to Eulophidae(Hymenoptera),on some Coleopteran beetles management,such as Octodonta nipae,one invasive species in southern China has been proved,with the mechanism unexplored.To make it clearly,the parasitoid virulence(the types of parasitic factors)of T.brontispae and the immune resistance(the immune response to ovarian,venom and parasitism)to its host O.nipae were investigated.The main results were shown as follows:1)Parasitic factors on the surface of T.brontispae eggs and their roles in defensing host's immune system.Data from scanning electron microscope and transmission electron microscope(TEM)indicated no existence of virus-like filament and polydnavirus,but appearance of a Helix pomatia lectin binding protein with a potential function in protecting eggs from encapsulation.Using degenerate primers of hemomucin,an adipocyte plasma membrane associated protein-like(TbAPMAP-like),a H.pomatia lectin binding protein,was obtained from T.brontispae.The transcript of TbAPMAP-like in eggs peaked at 2 h post-parasitization.Encapsulation analysis showed its function in protecting eggs from being encapsulated.2)The structure of venom apparatus and components of venom protein in T.brontispaeThe venom apparatus consists of an enteroid venom gland and a sphere or oval-shaped venom reservoir by light microscopy.The venom gland is composed of basal membrane,secretory cells,epithelial cell and intima,and the venom reservoir contains a thin muscle fiber,squamous epithelium cell and intima by transmission electron microscopy.Approximately 1505 venom proteins were identified by the combination of transcriptomic and label-free quantitative proteomic,and consistent with the classical venom protein characteristics,including enzymes,protease inhibitors,and some other proteins.The venom extracts also contained novel venom proteins,such as venom protein r-like protein.Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)analyses showed that most proteins were associated with processing and synthesis,which also confirmed the secretory function of the venom gland.3)Effects of parasitism,ovarian and venom protein on immune reaction of O.nipaeFive types of hemocytes,i.e.prohemocytes,plasmatocytes,granulocytes,spherulocytes and oenocytoids,were identified in the pupae of O.nipae by transmission electron microscopy and confocal laser scanning microscope.Granulocytes,plasmatocytes and oenocytoids were the main immunocytes.Parasitism by T.brontispae resulted in a significant increase in the percentage of granulocytes counts at 24 h,and subsequently a significant increase in the hemocytes viability and spreading ability at 96 h.Higher spreading ratio of granulocytes and plasmatocytes was observed at 24 and 48 h post-injection of the mixture of ovarian homogenate plus venom,respectively.These indicated a strategy that the absence of overt suppression of host immunity was taken by T.brontispae,and its ovarian and venom protein had the synergistic effect on host cellular immune reaction.Compared with unparasitized pupae,higher phenoloxidase(PO)activity was observed in parasitized O.nipae pupae at 12 and 72 h post-parasitization,along with a significantly longer melanization time at 96 h.Significant difference in PO activity was observed between PBS and the mixture of ovarian plus venom protein injected pupae.The results indicated that the humoral immunity of O.nipae could be triggered by T.brontispae's parasitism in the early stage,however,was restrained substantially in the late stage.In conclusion,the results in the present study implied that there was no polydnavirus or virus-like filament in T.brontispae,and venom was the main parasitic factor in T.brontispae.The effect of parasitism on immunity varied with time after parasitism.During the initial period after parasitism or injection of ovarian and/or venom,the immune response of O.nipae was activated,but melanization was inhibited during the early larvae period. |
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