Abstract

The effect of two temperatures (20 ^oC and 30 ^oC) on the toxicity of deltamethrin, and pirimiphos methyl against Sitophilus oryzae were studied using the residual film method. Results revealed that mortality increased proportionally with an increase in temperature, where the optimum temperature for toxicity of both tested insecticides was 30 °C either the mortality recorded at 24 or 48 hours after treatment. The insecticidal efficacy of five contact insecticides was also compared against Sitophilus oryzae (deltamethrin, imidacloprid, abamectin, emamectin benzoate and pirimiphos methyl at 30 ^oC temperature. Mortality of tested insecticides against rice weevils was recorded at 30 °C after 24 and 48 hours of exposure. Among the insecticides, deltamethrin was the most effective insecticide against rice weevils with median lethal concentration ranging from 0.48 to 0.35ppm followed by abamectin 0.682 to 0.399 and pirimiphos methyl with LC₅₀ 0.472 to 0.85ppm at 24 and 48 hours exposure periods, respectively. On the other hand, the other insecticides (emamectin benzoate and imidachloprid) were in-between according to the median lethal concentration recorded.

Keywords: Pirimiphos-methyl; Mammals; Organophosphorus; Emamectin benzoate; Sitophilus oryzae