Oxidative Stress Biomarkers in Helicoverpa armigera (Lepidoptera: Noctuidae) Exposed to Heavy Metal Contamination

Abstract

The concentration of heavy metal is quite hazardous to the life of people and the activities of insects. The study of the biomarkers of oxidative stress in the larvae of the Helicoverpa armigera was conducted in this experiment under the dietary unnatural conditions of cadmium (Cd), lead (Pb) and mercury (Hg) toxicity. Third larvae were fed 0, 5, 10, 25 and 50mg kg ^-1 of metal diets respectively during the 7 days. Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH) and malondialdehyde (MDA) are some of the biomarkers assessed in larval tissues. The dose-dependent accumulation of metals reached a maximum with Hg with the highest bioaccumulation factor of 4.8 0.3 at 50mg kg^-1. The enzyme activity of the antioxidants was biphasic, SOD increased to 25mg kg^-1 (Cd: 48.63.2μMg^-1 protein, 2.1folds over control) and then decreased at 50 mg kg-1. The same case happened with CAT and GPx where the max activities were 10-25mg kg^-1. At 50mg kg^-1 Cd, there was statistically significant (p< 0.05) increase in MDA of all metals to 3.4-0.2nmol mg^-1 protein (3.8-fold increase). The GSH loss was metal selective and Cd elicited highest loss (62.3±4.1% at 50mg kg^-1). The principal component analysis revealed that there was a set of biomarkers of each metal. The findings show that the biomarkers of oxidative stress prove useful in differentiating between heavy metals exposures and provide early alerts as to environmental contamination of insects. These results indicate the possibility of using H. armigera as a bioindicator species to detect heavy metal pollution in agroecosystems. The research will have a good contribution to assessment of environmental risks and sustainable management of pests and soil.