Selection for resistance of Spodoptera exigua to methoxyfenozide and preliminary study on the mechanisms of resistance

After 13 generations' selection in the laboratory,the methoxyfenozide-selected strain (Met-R) of Spodoptera exigua (Hubner) showed only a 4.19-fold increase in resistance to methoxyfenozide.Met-R showed no cross-resistance to chlorpyrifos,beta-cypermethrin,chlorfenapyr,tebufenozide or emamectin benzoate,with resistance ratio increases of 1.05-2.07-fold.In vitro biochemical studies showed that GST activity in the midgut of 5th instar larvae of Met-R was 2.44 times greater than in larvae of the susceptible strain (SS),indicating that enhanced GST activity may be associated with the resistance of S.exigua to methoxyfenozide.In contrast,nonspecific-esterase activity in Met-R showed no significant difference from that in SS,suggesting that nonspecific-esterase may not be involved in the resistance.