Effectiveness of spinosad and spinetoram against five stored-product beetle pests under high relative humidity conditions

The objective of this study was to evaluate spinosad and spinetoram effectiveness against S. granarius, S. oryzae, T. confusum, T. castaneum and R. dominica in wheat grain under high relative humidity (75%). The insecticides were applied at the rates of 0.5, 1 and 2 mg a.i./kg. Mortality was assessed after 2, 7, 14 and 21 days, and progeny reduction and grain damage caused by the insects were also assessed. All rates of both insecticides caused 98-100% mortality of R. dominica after 7 days, and 100% mortality after 14 and 21 days of exposure. Both insecticides achieved high mortality (97-100%) after 21 days of contact of S. granarius with 1 and 2 mg/kg, and S. oryzae with 2 mg/kg rate. The highest mortality of T. confusum and T. castaneum was recorded after 21 days of contact with 2 mg/kg of both insecticides, 54-55% and 25-31%, respectively. All rates of both insecticides caused high progeny reduction of >99% of R. dominica, >90% of T. confusum and 94% of T. castaneum (only with 2 mg/kg). The highest S. granarius progeny reduction (>90%) was found in wheat treated with 2 mg/kg spinosad and 1-2 mg/kg spinetoram, while the greatest progeny reduction of S. oryzae was observed in wheat treated with 2 mg/kg spinetoram. Wheat grain damage caused by R. dominica was very low, i.e. up to 0.2% in wheat treated with all rates of spinosad and spinetoram, while S. granarius and S. oryzae caused up to 5% damage only in wheat treated with 2 mg/kg of spinetoram.