An insect model for assessing mercury toxicity: Effect of mercury on antioxidant enzyme activities of the housefly (Musca domestica) and the cabbage looper moth (Trichoplusia ni)

Abstract

The effect of mercury as Hg₂Cl₂ and HgCl₂ on the antioxidant enzyme levels and its toxicity was investigated in an insect model comprised of adult females of the common housefly, Musca domestica, and fourth-instar larvae of the cabbage looper moth, Trichoplusia ni. HgCl₂ was found to be more toxic than Hg₂Cl₂ to both M. domestica and T. ni. The LC₅₀s for M. domestica were 1.17% and 0.38% w/v concentration for Hg₂Cl₂ and HgCl₂, respectively. For the more tolerant T. ni, the LC₅₀s were 5.15% for Hg₂Cl₂ and 0.96% w/w concentration for HgCl₂. The minimally acute LC₅ dose of both oxidation states of Hg was approximately 0.005% for both insects (w/v for M. domestica and w/w for T. ni). At the LC₅, both forms of Hg significantly induced the activity of superoxide dismutase in both insect species. Catalase was induced by both Hg₂Cl₂ and HgCl₂ in M. domestica but was only induced by HgCl₂ in T. ni. Glutathione-S-transferase, its peroxidase activity, and glutathione reductase activites were also significantly altered in most cases by Hg in both insects although the pattern of alteration was different between the two insects. It is evident that mercury induces oxidative stress in insects as it does in vertebrates. Our findings suggest that insects may serve as a valuable, non-mammalian model species to assess Hg-induced oxidative stress as a component of environmental toxicity.