Combination effect of azadirachtin and chlorantraniliprole with three synergists against a serious invasive agricultural pest Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm, Spodoptera frugiperda, isa newly invading polyphagous pest that affects crops such as maize, sorghum, and corn in India. The pest has developed resistance to various chemical insecticides, including Bt toxins and insect growth regulators. Therefore, there is an urgent need for alternative methods to manage this pest. The present study aimed to investigate the effect of three synergists in combination with pesticides. The results showed a high resistance ratio to chlorantraniliprole (RR-52.7) and low resistance to azadirachtin (RR-3.8) in the HSR field popu-lation compared to the susceptible population (Sus). In vitro enzyme inhibition experiments with PBO and TPP synergists revealed that resistance to chlorantraniliprole was mediated by esterase, GST and MFO. However less resistance to azadirachtin was mediated by esterase enzyme. The field population exhibited a 2.0-fold higher esterase activity (20 mu mol/min/mg protein) in re-sponse to chlorantraniliprole, followed by MFO activity (30-32 mu mol/min/mg protein). Gene ex -pression analysis revealed four genes (CYP321A7, CYP321B1, CYP4C71, and CYP4G74) were dif-ferentially expressed in the HSR population (4.0-6.0-fold) in chlorantraniliprole treatment and no expressions were seen in azadirachtin treatment. Overall the study concludes that, possible mechanism of chlorantraniliprole resistance in S. frugiperda mediated by P450s, esterases and GST and less resistance to azadirachtin by esterase suggesting that combination of synergists with azadirachtin could be useful for management of Spodoptera frugiperda.