In order to provide a more complete understanding of physiological impacts of IAA on insects, we investigated the cytotoxic effects of variable doses of IAA on hemocytes of Achoria grisella Fabr. (Lepidoptera: Pyralidae) larvae. The results revealed that addition of IAA (2 to 1,000 ppm) in diet of A. grisella larvae resulted in an increase in the total hemocyte counts at all doses tested. The percentage of plasmatocytes decreased but granulocytes increased at 2, 5, 100, 200 and 1,000 ppm. Nevertheless, the application of IAA did not alter mitotic indices, the percentage of spherulocytes, prohemocytes and oenocytoids. The percentage of living cells decreased at all treated doses compared to control interrelated with the elevated ratio of early apoptotic hemocytes at 5, 10, 50, 100 and 200 ppm. Significant reductions were observed at 2, 10, 50 and 100 ppm in the ratio of necrotic hemocytes, and at 10,100 and 200 ppm in the late apoptotic cells in IAA-treated A. grisella larvae. Our findings demonstrate that IAA exhibits detrimental effects on the hemocytes of A. grisella larvae that are the main components of insect immunity.