Cypermethrin and Methomyl Resistance in Helicoverpa armigera (Hubner)

The H. armigera larvae of the Mahaboobnagar district recorded a LD₅₀ of 29.125 μg larva⁻¹ and 59.609 μg larva⁻¹ at LD₉₀ for cypermethrin. The LD₅₀ and LD₉₀ values of cypermethrin for Raichur population of H armigera was 32.481 and 38.172 μg larva⁻¹, respectively. Toxicity of cypermethrin to Nagpur population of H. armigera showed that the LD₅₀ and LD₉₀ values were 20.069 and 54.708 μg larva⁻¹, respectively, The chi-square test revealed that the population used in the study was homogenous (^*p<0.05%). The H. armigera larvae of the Mahaboobnagar district recorded a LD₅₀ of 3.651 μg larva⁻¹ and 10.287 μg larva⁻¹ at LD₉₀ for methomyl. The LD₅₀ and LD₉₀ values of methomyl for Raichur population of H armigera was 3.630 and 10.417 μg larva⁻¹, respectively, while Toxicity of methomyl to Nagpur population of H. armigera showed that the LD₅₀ and LD₉₀ values were 2.652 and 7.214 μg larva⁻¹, respectively, when the chi-square test revealed that the population used in the study was homogenous (^*p<0.05%). From, the results obtained we can conclude that the continuous application of same chemistries across the generations increases the resistance from F₁ to F₃. Alternating with the new chemistries results in no cross resistance development as it was observed in all the three populations.