Relative toxicity of some important insecticides with particular reference to change in susceptibility level of Myzus periscae Sulz. to synthetic pyrethroids

The relative toxicity of emulsions of nine proprietary formulations of insecticides was evaluated against Myzus persicae Sulz., in the laboratory. On the basis of LC₅₀ values, fluvalinate, lambdacyhalothrin, deltamethrin, fenvalerate, alphamethrin, methyl demeton, cypermethrin and phosphamidon were respectively 209.3, 63.7, 40.8, 26.3, 9.0, 5.0, 3.9 and 1.4 times as toxic as fenproprathrin. All the synthetic pyrethroids were relatively more toxic than commonly used organophosphates, viz., methyl demeton and phosphamidon except cypermethrin and fenproprathrin indicating that these two pyrethroids may not provide effective control of M. persicae. Within a short span of three years, about 2-fold change in susceptibility level of M. persicae was observed, whereas it was two times more i.e., 4-fold with cypermethrin. A faster rate of development of resistance is thus expected with cypermethrin.