AN INSECT MODEL FOR ASSESSING MERCURY TOXICITY - EFFECT OF MERCURY ONANTIOXIDANT ENZYME-ACTIVITIES OF THE HOUSEFLY (MUCSA-DOMESTICA) AND THE CABBAGE-LOOPER MOTH (TRICHOPLUSIA NI)

The effect of mercury as Hg2Cl2 and HgCl2 on the antioxidant enzyme le vels and its toxicity was investigated in an insect model comprised of adult females of the common housefly, Musca domestica, and fourth-ins tar larvae of the cabbage looper moth, Trichoplusia ni. HgCl2 was foun d to be more toxic than Hg2Cl2 to both M. domestica and T. ni. The LC( 50)s for M. domestica were 1.17% and 0.38% w/v concentration for Hg2Cl 2 and HgCl2, respectively. For the more tolerant T. ni, the LC(50)s we re 5.15% for Hg2Cl2 and 0.96% w/w concentration for HgCl2. The minimal ly acute LC(5) 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 th e LC(5), both forms of Hg significantly induced the activity of supero xide dismutase in both insect species. Catalase was induced by both Hg 2Cl2 and HgCl2 in M. domestica but was only induced by HgCl2 in T. ni. Glutathione-S-transferase, its peroxidase activity, and glutathione r eductase activities were also significantly altered in most cases by H g in both insects although the pattern of alteration was different bet ween the two insects. It is evident that mercury induces oxidative str ess in insects as it does in vertebrates. Our findings suggest that in sects may serve as a valuable, non-mammalian model species to assess H g-induced oxidative stress as a component of environmental toxicity.