Toxicity of EC Formulation of Synthetic Pyrethroids on Jute Surface against Tribolium castaneum (Herbst)

The persistence of three pyrethroids, i.e. deltamethrin, cypermethrin and bifenthrin was studied on jute surface against susceptible as well as malathion resistant strain of Tribolium castaneum. Insecticides were sprayed at tfve doses of 10. 30, 50, 70 and 100 mg a.i. m⁻² and mortality was observed after 2, 30, 60, 90,120,150 and 180 d after spray. At recommended dose deltamethrin caused 80.0% mortality upto 180^th d and 66.7% upto 90 d against susceptible and resistant strain, respectively where as bifenthrin gave similar mortality upto 150 and 60 d, respectively. Cypermethrin at 30 mg a.i. m⁻² showed 76.7% mortality upto 90 d against susceptible insects but 63.3% mortality could be observed on 2^nd d with MR strain. Deltamethrin gave complete mortality at the highest dose to resistant strain upto 90 d, which was only upto 30 d with bifenthrin. The order of persistent toxicity of EC formulations of three pyrethroids for both the strains at all the doses were deltamethrin> bifenthrin>cypermethrin.