Influence of insecticides on the AChE activity in Spodoptera litura

Relative toxicity of selected organophosphate insecticides viz., profenofos and chlorpyriphos and carbamates viz., thiodicarb and methomyl were evaluated against third instar larvae of Spodoptera litura (Fabricius) of local (Rajendranagar) and Nalgonda populations. Besides, enzymatic studies were carried out to determine AChE activity in these populations treated with median lethal concentration of these insecticides. The results indicated that chlorpyriphos exhibited greater toxicity by topical application method after 24 hrs of treatment in both the populations. The AChE activity was the highest for profenofos with 78.8% with respect to control and lowest (48.7%) for thiodicarb in local population, while for Nalgonda population the values were 81.1% and 49.3%, respectively. Positive correlation between the toxicity and AChE activity was observed for organophosphates while no such correlation was seen for carbamates.