Nanoparticle-Assisted RNAi Targeting Small-Conductance Calcium-Activated Potassium Channels Enhances Insecticide Susceptibility and Disrupts Development in Spodoptera frugiperda

Spodoptera frugiperda is a globally invasive pest of Poaceae crops with extensive insecticide resistance, necessitating alternative control strategies. RNA interference (RNAi) was evaluated using the small-conductance Ca2+-activated K+ channel gene (SK) as a novel target. The SfSK gene exhibited conserved SK family features and was highly expressed in pupae and adults. Silencing of SfSK via dsRNA microinjection reduced transcript levels by up to 42.6% and significantly increased larval susceptibility to emamectin benzoate and λ-cyhalothrin, with a maximum increase of 26.7% in mortality. Encapsulation of dsRNA in chitosan-tripolyphosphate (CS-TPP) nanoparticles protected against enzymatic degradation and substantially enhanced silencing efficiency. Correspondingly, injection of CS-TPP-dsSfSK increased larval mortality by up to 36.7% and 30% with emamectin benzoate and λ-cyhalothrin treatments, respectively. Moreover, oral administration also enhanced susceptibility, delayed pupation, and reduced the level of adult emergence, indicating developmental disruption. These results highlight the potential applications of CS-TPP-dsSfSK nanoparticles for RNAi-mediated pest management.