Abstract:To explore the effects of parasitization by Cotesia chilonis (Matsumura) on larval immune reactions of Chilo suppressalis (Walker), the changes in the total number, spreading, viability, phagocytosis and encapsulation capacity of hemocytes, and phenoloxidase activity of hemolymph in parasitized larvae of C.suppressalis were observed and measured. The total number of hemocytes in parasitized larvae became significantly higher than that of unparasitized control from 1 day post-parasitization. The numbers of granulocytes and plasmatocytes in parasitized larvae, showed a similar pattern of variation with the total number of hemocytes, began significantly higher at 3 days and 0.5 day post-parasitization, respectively. However, the percentages of these two types of hemocytes in the total number of hemocytes from parasitized larvae were almost not significantly different with their unparasitized controls. The spreading behavior of host hemocytes was markedly inhibited at 0.5 day post-parasitization. After then, it showed no significant difference with the unparasitized control. The mortality of hemocytes in host larvae increased after oviposition. Hemocytes phagocytosis of parasitized larvae reduced significantly at 2 days post-parasitization, while the encapsulation capacity of hemocytes reduced significantly at 1 day post-parasitization. It showed a dramatic increase with further decrease in phenoloxidase activity of hemolymph in parasitized larvae. The results suggest that the parasitization by C.chilonis may result in some regular changes of immunoreactions of its host C.suppressalis.