The toxicity of certain commonly used insecticides was evaluated against cotton aphid, Aphis gossypii to assess the shift in level of susceptibility. There was a shift in the level of susceptibility of A. gossypii after three years. The LC50 and LC90 values of endosulfan, monocrotophos, dimethoate, acephate and cypermethrin were increased 1.63, 1.92, 2.84, 1.47 and 2.19, 4.24, 3.42, 5.92, 2.98, 4.13 folds respectively. A comparison of LC90 values with recommended concentrations of test insecticides also revealed that aphid population of Guntur district developed resistance to the test insecticides. Among the new insecticides, acetamiprid was highly toxic followed by diafenthiuron and thiamethoxam were recommended for managing A. gossypii.
Aphis gossypii, Cossypium hirsutum, Insecticide resistance
