Abstract: In order to investigate the effects of Pteromalus puparum venom on the encapsulation and phagocytotic capacities of granulocytes (GRs) and plasmatocytes (PLs) in its host, Pieris rapae, we first purified these two types of host hemocytes using Na₂-EDTA treatment and nylon wool method, respectively. Then, with the method of cell culture in vitro we also studied the different roles of GRs and PLs in host encapsulation and phagocytosis, and the effects of parasitoid venom targeting to these two cellular responses. The results indicated that both GRs and PLs took part in the host encapsulation. The encapsulation performed by GRs was stronger than by PLs. The highest rate was presented in encapsulation reaction mediated by the mixture of GRs and PLs. The host cell-free plasma did not significantly influence the encapsulation performed by GRs and PLs, respectively. The encapsulation capacities of GRs and PLs were both markedly inhibited by the parasitoid venom in a dose-dependent manner. Additionally, in the host, both GRs and PLs possessed the phagocytotic capacity. The phagocytotic capacity of GRs was much stronger than that of PLs. Parasitoid venom also noticeably suppressed the phagocytosis performed by GRs and PLs, respectively, also in a dose-dependent manner. The results suggest that both GRs and PLs in the host, P. rapae, play key roles in the host cellular responses, and P. puparum venom can significantly decrease host cellular responses including encapsulation and phagocytosis performed by GRs and PLs.

Key words:  Pieris rapae, Pteromalus puparum, venom, granulocyte, plasmatocyte, encapsulation, phagocytosis