Relationship between esterase I₅₀ and toxicity of different organophosphate insecticides to Helicoverpa armigera (Hubner) collected from two different regions of Punjab

The esterases are involved in providing resistance to H. armigera against insecticides, the study was undertaken to correlate its I₅₀ from different regions of Punjab. Acephate amongst all organophosphates emerged to be the most effective in inhibiting the esterases. LC₅₀ and esterases I₅₀ for quinalphos and chlorpyriphos registered a positive correlation in the population of insects collected from Abohar and Ludhiana. Whereas, in acephate and triazophos such correlation could not be established as there was a little difference in their LC₅₀ values. Hence esterase I₅₀can be used as a tool to monitor insecticide resistance level for selective insecticides only. In vitro inhibition of different isozymic bands of esterases revealed that less number of esterase isozymes were inhibited with quinalphos in the Abohar population as compared to that of Ludhiana, may be due to higher LC₅₀ of Abohar region.