Initial efficacy of pyrethroids, inert dusts, their low-dose combinations and low temperature on Oryzaephilus surinamensis and Sitophilus granarius

In this study, initial efficacy of three pyrethroids, two inert dusts and their low-dose combinations were investigated on adults of Sitophilus granarius and Oryzaephilus surinamensis at laboratory conditions. The insects were exposed to treatments on concrete surface. The LC₂₅ values of the pyrethroids and LD₂₅ values of the inert dusts were estimated and used for determining their combination effects. Mortality of insects was recorded 48 h after treatments. The effect of a low temperature, −18 °C was also assessed on both species. Exposure times to −18 °C were 15, 18, 22, 27, 33 and 40 min for S. granarius and 10, 12, 15, 19 and 23 min for O. surinamensis in main experiments. The treated insects were kept in the laboratory conditions for 24 h after cold treatments, then the mortalities were recorded. The LC₅₀ values estimated for deltamethrin, lambda-cyhalothrin and fenvalerate on S. granarius were 45.08, 43.34 and 465.00 mg ai/L; and on O. surinamensis were 0.65, 1.83 and 81.36 mg ai/L, respectively. The LD₅₀ estimated for zeolite on S. granarius was 10.32 g/m²; and kaolin was not effective on this species. The LD₅₀ values estimated for zeolite and kaolin on O. surinamensis were 7.7 g/m² and 12.0 g/m², respectively. Mortalities caused by deltamethrin + zeolite and lambda-cyhalothrin + zeolite combinations on S. granaries were 80.0% and 63.3%, respectively. The effects of combinations of the pyrethroids and zeolite or kaolin on O. surinamensis were also significantly higher than sum of their individual effects. It means the effects of these combinations were synergistic. The LT₅₀ values estimated at −18 °C were 33 min for S. granarius and 16 min for O. surinamensis. The results obtained from this study can be used as basic and preliminary information for practical control programs of these pests in stored products.