Relative Toxicity of Soil Insecticides against Polyphylla Grubs (Harris) (Scarabaeidae: Coleoptera)

Six commercially available insecticides viz., chlorantraniliprole, bifenthrin, clothianidin, thiamethoxam, imidacloprid and chlorpyriphos were evaluated against the Polyphylla grubs under laboratory conditions. The observations on mortality were recorded at different doses after 48 hours of treatment. For second instar grubs, the order of toxicity on the basis of LC₅₀ value was chlorantraniliprole > bifenthrin > thiamethoxam > clothianidin > imidacloprid being 4.49, 3.88, 2.69, 2.61 and 1.07 times toxic than chlorpyriphos, whereas for third instar grubs, the order of toxicity was chlorantraniliprole > bifenthrin > clothianidin > thiamethoxam > chlorpyriphos with toxicity of 3.85, 3.59, 1.33, 1.22, 1.16 times than imidacloprid. Based on the lethal concentrations and relative potencies, chlorantraniliprole was found to be most effective insecticide, showing highest relative toxicity against second and third instar grubs of Polyphylla as compared to other insecticides.