Insects are model organisms for immunological studies. The cellular and the antioxidant enzyme responses of insects are major bioindicators against environmental stresses (metal exposure, infection, etc.). In our study, the differences in the hemocyte counts and the antioxidant enzyme activities of Hyphantria cunea larvae exposed to the different amounts of zinc, copper, and nickel and Bacillus thuringiensis infection were determined. With metal exposure, the superoxide dismutase, catalase, and

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... glutathione peroxidase activities increased, but the hemocyte counts decreased. Additionally, both the hemocyte counts and the enzyme activities increased with Bacillus thuringiensis infection. As a result of this study, we found that the superoxide dismutase, catalase, and glutathione peroxidase and the hemocyte counts varied in response to both metal exposure and bacterial infection.