Functional analysis of Sf-NPF1 in food intake and antifeedant induction by azadirachtin in Spodoptera frugiperda larvae

Azadirachtin, a highly effective botanical pesticide, demonstrated notable biological activities against Spodoptera frugiperda , including mortality induction, growth and development inhibition, and antifeedant effects. Neuropeptide F (NPF) has been shown to play a role in various physiological processes in insects. Nonetheless, the functions of Sf- NPF1 in regulating food intake and antifeedant induction by azadirachtin in S. frugiperda larvae are yet to be elucidated. In this study, the antifeedant effects induced by 0.5 and 1.0 μg/g azadirachtin treatments in S. frugiperda larvae were evaluated. The sequence of Sf-NPF1 was identified with two transcript variants, and the proteins exhibit high identity with NPFs found in lepidopteran insects. Spatiotemporal expression analysis indicated that Sf-NPF1 exhibited high expression levels in first instar larvae and male adults, while the lowest expression was observed in non-feeding stages (egg and pupa stages). Besides, Sf-NPF1 also demonstrated notable expression in the midgut tissue of larvae. Azadirachtin treatments inhibited the expression of Sf-NPF1 in the larval midgut. The injection of the Sf- NPF1a mature peptide resulted in increased larval food intake and weight gain during a two-day treatment period. The antifeedant effect induced by 1.0 μg/g azadirachtin was also mitigated by the injection of Sf- NPF1a mature peptide. Our results indicated that Sf- NPF1 may serve as a positive regulator of food intake in S. frugiperda larvae, while azadirachtin could exert an antifeedant effect in larvae via inhibiting the expression of Sf-NPF1 . These findings establish a foundation for comprehending the mechanism behind the antifeedant effect induced by azadirachtin in insect larvae and provide a potential target for developing novel insecticides.