Efficacy of some pesticides against Tetranychus urticae Koch (Acari: Tetranychidae) and their residual effects on Coccinella septempunctata (L.) (Coleoptera: Coccinellidae)

Abstract

Pesticides are used to control Tetranychus urticae Koch populations in country bean, Dolichos lablab (L.). The results of using pesticides are more predictable if there is detailed information about their toxicity and specificity. In particular, the degree of pesticide exposure is associated with the adult stages of T. urticae and natural enemies, while determining the overall efficacy of pesticide use. The present study was carried out to determine the direct and residual effects of seven pesticides, namely abamectin, abamectin + bifenthrin, spinosad, chlorfenapyr, deltamethrin, imidacloprid and thiamethoxam against Tetranychus urticae Koch (Acari: Tetranychidae) and residual toxicity of these pesticides against the pest and its predator Coccinella septempunctata (L.) (Coleoptera: Coccinellidae) adults. In the laboratory trials, abamectin caused 100% mortality of T. urticae within 3 h, abamectin + bifenthrin within 6 h and other pesticides within 48 h except for imidacloprid and thiamethoxam. When the toxicity of T. urticae eggs was examined, the egg mortality for all pesticide treatments was significantly higher than the control. Abamectin + bifenthrin and chlorfenapyr caused 100% egg mortality followed by application of abamectin (95%) and deltamethrin (82%). On the other hand, thiamethoxam, imidacloprid and spinosad showed 63%, 65% and 71% egg mortality, respectively. In potted bean plants, abamectin, abamectin + bifenthrin and chlorfenapyr showed significant mortality of T. urticae over control up to 21 days and the rest of the pesticides showed up to 14 days. Abamectin and chlorfenapyr showed higher residual efficacy against T. urticae but low toxicity against C. septempunctata. Imidacloprid had the longest residual effect on adults of C. septempunctata causing 20% mortality after 21 days, but low toxicity against T. urticae. Abamectin + bifenthrin residue caused > 20% mortality of C. septempunctata after 14 days of exposure. Therefore, abamectin and chlorfenapyr can be used for the management of T. urticae because of their higher toxicity against T. urticae and low residual activity against C. septempunctata.