Susceptibility of Rice Weevil Sitophilus oryzae (L.) to Abamectin, Permethrin, Thiamethoxam, Chlorpyrifos and Malathion

Residual insecticides have traditionally been used to control the stored cereals, through treating the structure of stores or surface of the commodities. The efficacy of abamectin, permethrin, thiamethoxam, chlorpyrifos and malathion were evaluated against rice weevil, Sitophilus oryzae (L.) via the insecticide-treated surface. Then, persistence of their insecticidal property, their lethality against the starved adults and their effect against the number of F1 adults were investigated. The LC50s of abamectin, permethrin, thiamethoxam, chlorpyrifos and malathion were 1.04, 38.7, 3.56, 0.16 and 0.86 mg ai/l, respectively, based on probit analysis of the 24 hours post-treatment data. Decrement of F1 progenies were between 38 to 87 % (both in low and high concentrations of chlorpyrifos, respectively). In persistence experiments, thiamethoxam (17% reduction of mortality) and malathion (93% reduction of mortality) were the most and least persistent insecticides, respectively. Susceptibility to some concentrations of chlorpyrifos, malathion and thiamethoxam were significantly increased as a result of starving the insects. Efficacy of low concentration of thiamethoxam (1.25 mg ai/l) was increased as consequence of starving the beetles for 14 days (26 to 83%). Our results demonstrated that effectiveness of the residual insecticides can be increased through their appropriate application and sanitation of grain stores.