Methoxyfenozide belongs to a group of biorational insecticides known as insect growth regulators which
is used in the control lepidopteran insect pests. Here we report a field collected population of Spodoptera
litura selected with methoxyfenozide for thirteen consecutive generations resulted in the development of
83.24 and 2358.6-fold resistance to methoxyfenozide as compared to parental field population and susceptible
laboratory population, respectively. The outcomes of synergism studies revealed methoxyfenozide
resistance in S. litura to be monooxygenases (MO) mediated with high synergistic ratio (4.83) with
piperonyl butoxide (PBO), while S,S,S-tributyl phosphorotrithioate (DEF) showed no synergism with
methoxyfenozide (SR = 1). This methoxyfenozide resistant strain showed a high cross resistance to
deltamethrin (28.82), abamectin (12.87) and little to emamectin benzoate (2.36), however no cross
resistance of methoxyfenozide and other tested insecticides was recorded. The results depicted the
methoxyfenozide resistance in S. litura to be unstable with high reversion rate which decreased from
2358.6 to 163.9-fold (as compared to susceptible strain) when reared for five generations without any
insecticidal exposure. The present research supports the significance of MO-mediated metabolism in
resistance to methoxyfenozide, which demands some tactics to tackle this problem. The resistance
against methoxyfenozide in S. litura can be overcome by switching off its use for few generations or
insecticides rotation having different mode of action.