Abstract:The number changes of plasmatocytes and granular cells in both female and male pupae of Pieris rapae (Lepidoptera: Pieridae) and Papilio polytes (Lepidoptera: Papilionidae) at different times after parasitism by Pteromalus puparum (Hymenoptera: Pteromalidae) were measured using a neubauer hemocytometer so as to define effects of the parasitism by this parasitoid on the hemocyte population of its two hosts. By comparison with unparasitized pupae, the parasitism by this parasitoid resulted in a significant increase with the maximum of about 20 times in the total number of hemocytes in P.rapae except parasitized pupae on the 2nd day post parasitization. No marked difference in the percentage of both plasmatocytes and granular cells between P.rapae pupae parasitized for 0.5 and 5 days and their corresponding control pupae was found. From first to fifth day after parasitism, the percentage of plasmatocytes significantly decrease, conversely, the proportion of granular cells increased. In contrast, the total number of hemocytes in P.polytes pupae from half a day to third day after parasitism did not displayed apparent changes by comparison with unparasitized pupae, while appeared a marked increase with the maxi- mum of about 3 times. As to the percentage of plasmatocytes and granular cells in P.polytes pupae from half a day to fifth day after parasitism, the former showed significantly decreased and the latter increased. The results concluded that the parasitism by this parasitoid for a defined period could result in not only a noticeable increase in total hemocyte number and the percentage of granular cells in its two hosts tested, but also a marked decrease in the proportion of plasmatocytes.