Combined Action of Piperonyl Butoxide with Some Insecticides, Against the Lesser Grain Borer Rhylopertha Dominica (Coleoptera: Bostrichidae)

Abstract

The toxicity of four (4) commercially formulated insecticides viz. organophosphate, pyrethroid, neonicotinoid and organo carbamate was investigated following residual-film method. 7 days old adults was used in this experiment. The data was recorded after 24 hours of treatment. All tested insecticides showed satisfactory killing ability towards the beetle tested. The insecticides were highly or moderately toxic to adult with LD50 values of 0.0745 (chloropyrifos), 0.7182 (cypermethrin), 1.9997 (imidacloprid) and 3.6513 (carbaryl) respectively. Chloropyrifos was found most toxic and carbaryl was less toxic to adult. The order of toxicity was chloropyrifos > cypermethrin> imidacloprid > carbaryl. Synergistic effect of piperonyl butoxide (PBO) in combination with all the insecticides tested was also investigated. The synergistic effects were calculated by using co- toxicity coefficient (>100) values. piperonyl butoxide considerably increased the toxicity of all the insecticides except of chloropyrifos. PBO did not produce synergistic effect against the adult. The interaction between insecticides and synergist was analyzed by co-toxicity coefficients and through plotting isoboles of the LD50 values.