Synergistic effects of Zn, Cu, and Ni and Bacillus thuringiensis on the hemocyte count and the antioxidant activities of Hyphantria cunea Drury (Lepidoptera: Arctiidae) larvae

In nature, insects are constantly exposed to various environmental stressors. Heavy metals are one of the important factors of environmental pollution. Heavy metals can cause adverse effects on the growth rate and the survival of herbivores, as well as immune function. In addition to heavy metals, another factor that insects are exposed to in nature is entomopathogens. The cellular and the antioxidant enzyme responses of insects are major bioindicators against the stressors. In this 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 glutathione peroxidase activities increased, but the hemocyte counts decreased. Additionally, both the hemocyte counts and the enzyme activities increased with Bacillus thuringiensis infection. Although heavy metal exposure decreased the hemocyte counts and increased the antioxidant enzyme activities, the increase in the hemocyte counts with bacterial infection and the increased antioxidant enzyme activities demonstrated that the response to infection in the insect was stronger and the synergistic effect was occurred. As a result of this study, we found that the activities of superoxide dismutase, catalase, and glutathione peroxidase and the hemocyte counts varied in response to both metal exposure and bacterial infection.