Effectiveness of pirimiphos-methyl, alpha-cypermethrin, spinetoram and thiamethoxam alone and in combination with diatomaceous earth for the control of Trogoderma granarium on rough rice

Abstract

The khapra beetle, Trogoderma granarium Everts, is a serious threat to stored commodities with the potential to develop tolerance to insecticides. Binary combinations of insecticides with diatomaceous earth are usually considered effective grain protectants for the control of T. granarium. However, studies that directly compare their efficacy in rough rice are few. We examined control efficacy of pirimiphos-methyl, alpha-cypermethrin, spinetoram and thiamethoxam (at 0.1, 1 or 10 ppm) alone or in binary combinations with diatomaceous earth (DE; at 500 or 1000 ppm) against T. granarium on rough rice grains. The highest mortality (100 %) of T. granarium larvae was observed at the combination of pirimiphos-methyl (10 ppm) + DE (1000 ppm) after 14 days of exposure, and at the combinations of pirimiphos-methyl (1 ppm) + DE (1000 ppm); alpha-cypermethrin or spinetoram (10 ppm) + DE (1000 ppm) after 21 days of exposure. The mixture of thiamethoxam (10 ppm) + DE (1000 ppm) resulted in 90 % mortality of T. granarium after 21 days of exposure. Except thiamethoxam, mixtures of insecticides and DE resulted in complete suppression of F1 and F2 progeny at their highest rates. Moreover, after 90 days of exposure, the mixtures of insecticides with DE proved more effective in reducing grain weight loss than their individual applications. In conclusion, the data of the present study revealed that the binary combinations of insecticides and DE are likely to help manage T. granarium in stored rice.