Iranian diatomaceous earth as a control agent for protection of paddy rice against Sitotroga cerealella (Oliv.) (Lepidoptera, Gelechiidae) and its delayed effects on physicochemical properties of paddy rice

Sitotroga cerealella (Oliv.) (Lepidoptera: Gelechiidae) is one of the destructive insect pests of paddy rice in grain storage facilities and warehouses. For this study, the insecticidal activity of a new Iranian DE formulation, Dryasil, was evaluated against S. cerealella fourth instar larvae on three varieties of paddy rice: Hashemi, Khazar, and Champa. The bioassays were carried out at the concentrations of 400 and 1000 mg/kg and four temperature levels (15, 20, 25, and 30 °C) after 7, and 14 d of exposure interval. The effects of this protectant were also investigated on the quality of the treated-paddy rice after three months of storage. In all tested varieties, mortality of the exposed larvae increased with increased concentration of DE and exposure period. The activity of DE was higher at 30 °C than other tested temperatures. The highest larval mortality (69.80%) was reported in Khazar variety treated with 1000 mg/kg at 30 °C. The larvae were well controlled in Khazar and then Hashemi variety. The DE had no adverse effects on water absorption rate, volume expansion ratio, cooking time, and chalkiness percentage. Overall, our findings suggest that Dryasil could be considered as a grain protectant that does not adversely affect the properties of different paddy rice varieties to control S. cerealella.