Efficacy of Certain Insecticides against Lipaphis erysimi (Kalt.) and Their Relative Toxicity against Predatory Coccinellid Beetle

The efficacy of certain new insecticides viz., imidacloprid, bifenthrin, lambda-cyhalothrin each at three different concentrations along with dimethoate and deltametnrin (as standard check) against mustard aphid, Lipaphis erysimi (Kalt.) on rapeseed (variety TS-38) and their relative toxicity against adult coccinellid beetle, Coccinella septempunctata was studied. All the insecticidal treatments were found to be significantly superior over control (untreated). Among the insecticides, the lowest incidence and the highest population reduction of the aphid population was obtained with imidacloprid at 30 g a.i./ha followed by imidacloprid 20 g a.i./ha and imidacloprid 10 g a.i./ha after one d, seven d and fifteen d of spraying. The highest mean yield was obtained from the experimental trial treated with imidacloprid 30 g a.i./ha (7.32 q/ha) followed by imidacloprid 20 g a.i./ha (7.05 q/ha) and the lowest was obtained at untreated plots (5.12 q/ha). The highest benefit-cost ratio was registered with imidacloprid 20 g a.i./ha (4.49:1) followed by imidacloprid 30 g a.i./ha (4.21:1) which successfully reduced the aphid population. The LC₅₀ values of imidacloprid, bifenthrin, lambda-cyhalothrin, dimethoate and deltametnrin against C. septempunctata were found to be 1.44, 0.47, 1.20, 0.77 and 0.74% after 24 h, respectively. The order of toxicity on the basis of LC₅₀ values was bifenthrin > deltamethrin > dimethoate > lambda-cyhalothrin > imidacloprid. Taking deltamethrin as unity, the order of relative toxicity were bifenthrin (1.57) > dimethoate (0.97) > lambda-cyhalothrin (0.61) > imdacloprid (0.51) after 24 h. Based on the aphid population reduction, yield and benefit-cost ratio imidacloprid 20 g a.i./ha can be considered sufficient to control the L. erysimi population infesting rapeseed. Considering the LC₅₀ values and relative toxicity against C. septempunctata, imidacloprid had an added advantage over other tested chemicals.