Susceptibility Change in Male Helopeltis Theivora Waterhouse (Jorhat Population) to Different Classes of Insecticides

By using dry film bioassay method, relative toxicity of thirteen insecticides was evaluated against the male Helopeltis theivora (Jorhat population, Assam). On the basis so LC₅₀ values, the order of toxixity was found to be cypermethrin > γ-cyhalothrin > fenpropathrin > thiomethoxam > acephate > profenophos > deltamethrin ana dimethoate > oxydemeton methyl > imidacloprid > phosalone > quinalphos > endosulfan. As compared to endosulfan, cypermethrihr γ-cyhalothrin and fenpropathrin were 26.8, 24.8 and 16.0 times toxic. Effective field dosages of the thirteen insecticides were computed based on LC₅₀ values and compared with the recommended dosaqe. Pronounced shift in the level of susceptibility of male H. theivora was noticed to all the chosen insecticides (1.04 - 88.9 times increase) except acephate. The decrease in susceptibiilty of H. theivora to deltamethrin and imidacloprid was the maximumu Monitoring of resistance development in field populations of H. theivora in northeast India could db made by using these baseline values of different insecticides.