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

<i>Spodoptera frugiperda</i> 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 (<i>SK</i>) as a novel target. The <i>SfSK</i> gene exhibited conserved <i>SK</i> family features and was highly expressed in pupae and adults. Silencing of <i>SfSK</i> via dsRNA microinjection reduced transcript levels by up to 42.6% and significantly increased larval susceptibility to emamectin benzoate and <i>λ</i>-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-ds<i>SfSK</i> increased larval mortality by up to 36.7% and 30% with emamectin benzoate and <i>λ</i>-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-ds<i>SfSK</i> nanoparticles for RNAi-mediated pest management.