Baseline susceptibility and stability of insecticide resistance of spodoptera litura (F.) (Lepidoptera: Noctuidae) in the absence of selection pressure

A population of spodoptera litura collected from dunyapur was reared for eleven generations under laboratory conditions without any insecticide exposure. the lc 50 data was recorded through diet incorporation method against four insecticides such as emamectin benzoate,spinosad,imidacloprid and profenofos. for new chemistry insecticides the larval mortality data was taken after 72 hrs while in case of conventional insecticides the mortality data was taken after 48 hrs. emamectin benzoate (1.59 ppm) was found to be most toxic on the basis of lc 50 values followed by spinosad (7.77 ppm),profenofos (686.5 ppm) and imidacloprid (258.75 ppm) at generation 1. the decrease in the lc 50 values after 11 generations as compared to the field population of s. litura was 4.81,9.83,9.3 and 13.82 folds against emamectin benzoate,spinosad,imidacloprid and profenofos,respectively. the estimated decrease in resistance was 11.36,11.11,16.67 and 9.61 for imidacloprid,spinosad,emamectin benzoate and profenofos,respectively. the results suggest that spinosad can be included in the control program of s. litura,due to its lower stability and higher reversion rate with insecticides bearing novel modes of action and this baseline susceptibility data could be very helpful in future monitoring of insecticide resistance in s. litura. copyright 2011 zoological society of pakistan.