Effect of spinosad and malathion on esterase enzyme activities of Tribolium castaneum (Coleoptera: Tenebrionidae)

Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is a major pest belongs to the most widespread and destructive pests of stored products. This pest may cause considerable economic losses therefore numerous insecticides have been used for its management. This pest resistance to chemical insecticides and the management programs failure have been reported in several documents. Bioassay and detoxifying enzymes levels in T. castaneum were evaluated using different spinosad and malathion insecticides concentrations in this study. Insects were exposed to contact toxicity of the insecticides for 24 h in laboratory condition (25±5 °C in darkness). Bioassay results showed that the spinosad had had more effects than malathion. Also LC50 ratio range showed the insecticides LC50 was significantly different against T. castaneum. Detoxifying enzymes assay was performed in four insecticides concentrations (LC10, LC25, LC50 and LC75) and showed that level of esterase enzymes exposed to malathion was higher than spinosad in using alpha and beta-naphtyl acetate as substrate. It is concludedrnthat susceptibility of the T. castaneum against both insecticides were different and these differences were obvious in their enzymes activity as well.