Abstract: 　Objective To explore the possible defensive immunity of Culex pipiens quinquefasciatus larvae after being infected by Lagenidium giganteum . Methods To count and analyze morphologically hemocytes of the mosquito larvae with Giemsa's stain and by both phase contrast microscope and ordinary microscope. Results ① Following the prolonged duration of infection, the number of hemocytes featured as increase, intense increase and gradual decrease. ② 48 and 72 h after infection the proportion of plasmatocytes and granulocytes increased significantly, but that of prohemocytes showed a relatively slow increase, while 96 and 120 h after infection the proportion of spherulocytes and oenocytoids increased gradually and that of plasmatocyte and granulocytes showed a slow decrease. ③ After L. giganteum infection, vacuolation and morpholysis were found in plasmatocytes. Conclusion The changes of hemocytes in amount,classification and morphology after infection revealed that Lagenidium giganteum can induce some defensive immune reactions in the larvae of Culex pipiens quinquefasciatus possibly due to a release of antigens or toxic substances by the fungus.

Key words: Culex pipiens quinquefasciatus larva, Lagenidium giganteum, hemocyte, defensive immunity