Contact effects of the five insecticides against rice weevil Sitophilus oryzae and influence of starvation in its susceptibility

Treating grain bins, grain stores and other surfaces is one of the traditional and effective methods forcontrol of stored products insects. In this study, toxicity of insecticides, abamectin, chlorpyrifos, malathion,permetrin and thiamethoxam against rice weevil, Sitophilus oryzae and also possibility of alternate currentinsecticides by thiamethoxam, a relatively safe insecticide, were investigated. Bioassays were conducted bymeans of exposing adults to treated surfaces of petri plates by formulations. LC50 values of the insecticideswere 1.05, 0.16, 1.14, 38.75 and 3.56 mg ai/L, respectively. Another set of bioassays were carried out bythree low, medium and high concentrations, based on the preliminary experiments. These treatments werereplicated three to five times. Following these assays, the possible change in susceptibility of adults via 24and 48hrs starvation was evaluated using the last concentrations. The possible decreasing efficiency ofinsecticides residues were investigated via postponing of exposing insects, for 24 and 48hrs, to treatedcontainers. In a few treatments significant increased mortality was observed, but more mortality values wererecorded in over half of treatments. Residues of insecticides had relatively the same toxicity of fresh onesafter 24hrs, but its effect were to some extent decreased after 48 hrs. The reductions were mostly documentedin the low concentrations. Based these results, thiamethoxam is an appropriate alternative for currenthazardous insecticides.

کلیدواژه ها:

Contact toxicity ، Rice weevil ، Thiamethoxam