Toxicity and persistence of selected neonicotinoid insecticides on cowpea aphid,Aphis craccivoraKoch (Homoptera: Aphididae)

Field strain of cowpea aphid, Aphis craccivora Koch, was treated by selected neonicotinoid insecticides to evaluate their toxicity and persistence against this pest in Assiut governorate, Egypt. Under faba bean field conditions, acetamiprid, imidacloprid, thiamethoxam and dinotefuran registered significantly high percent reduction of the pest at one, seven, fifteen and 21 post treatment. The residual effects of these insecticides showed that the LT50 for acetamiprid, imidacloprid, thiamethoxam and dinotefuran were 5.8, 6.2, 6.95 and 4.2 days, respectively. The application of these insecticides on the cowpea aphid under field conditions induced yield increases. The toxicity of these neonicotinide insecticides were tested against field strain of cowpea aphids using leaf-dib bioassay under field and laboratory conditions. The toxicity index showed that thiamethoxam, acetamiprid and imidacloprid have the highest aphicidal activity, with LC50s 0.60, 0.71 and 1.16 mg/L, respectively, while dinotefuran was the least toxic one with LC50 23.41 mg/L. Results of this study indicated that neonicotinoid insecticides were highly effective against cowpea aphid under field and laboratory conditions.