Chitosan–Alginate-Loaded Spinosad: Enhanced Cytotoxicity and Insecticidal Activity against Spodoptera frugiperda

Spinosad (Spi) is a promising insecticide with a novel mode of action and favorable environmental safety, but its field efficacy is severely limited by environmental instability, which restricts its preventive application. In this study, spinosad-loaded chitosan-sodium alginate particles (CS-ALG@Spi) were successfully fabricated and systematically characterized. The prepared microspheres exhibited regular morphology, suitable particle size, good dispersion, and satisfactory dilution stability. Compared with free Spi, CS-ALG@Spi showed significantly enhanced UV stability and an obvious acid-responsive release profile. Bioassays indicated that the formulation displayed remarkably improved insecticidal activity against Spodoptera frugiperda. It caused severe structural damage to the larval midgut and increased the activities of antioxidant enzymes. In vitro cytotoxicity assays revealed that the formulation exerted pronounced cytotoxic effects by inducing reactive oxygen species accumulation, eliciting G2/M cell cycle arrest, and decreasing mitochondrial membrane potential. Our study provides a reliable and eco-friendly strategy for the development of efficient pesticide delivery systems.