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Effects of temperature and light exposure on the toxicity of deltamethrin, chlorpyrifos-methyl, and malathion against Tribolium castaneum were extensively studied using the residual film method. Results revealed that mortality increased proportionally with an increase in temperature, where the optimum temperature for the three tested insecticides was 30°C. Toxicity of the tested insecticides could be arranged in the following descending order: chlorpyrifos-methyl >deltamethrin >malathion. Moreover, light exposure obviously enhanced toxicity of the three investigated insecticides compared to dark exposure. Piperonyl butoxide (PB) acted as an oxidase inhibitor, when mixed with each of the three insecticides, increased the toxicity ratio by about four fold in both dark and light. Joint toxic effects between deltamethrin and the two tested OP as esterase inhibitors, showed that mixing chlorpyrifosmethyl with deltamethrin increased deltamethrin toxicity by 152.7 and 137.12 fold in dark and light, respectively. Finally, deltamethrin + chlorpyrifos-methyl + PB blend was found to possess maximum efficiency, which increased deltamethrin toxicity by 679.05 fold under exposure to light conditions. Thus, modification of deltamethrin toxicity by increased temperature; light exposure and detoxification inhibitors maximized its toxicity to Tribolium castaneum, reduced insecticide rate, and thus reduces both the environmental stress, and the resistance pressure.