A Nano-Delivery System Enhances the Stomach Toxicity of Methoxyfenozide against Spodoptera litura by Suppressing the Synthesis of Insect Cuticle Protein

There is a growing demand for applying green pesticides instead of traditional synthetic pesticides to minimize potential threats to food and environmental safety. Insect growth regulators (IGRs) are regarded as a secure alternative, but their control efficacy needs to be improved to meet actual demands. Herein, a star polymer (SPc) was constructed and applied as an efficient pesticide nanocarrier, which could be spontaneously conjugated with IGR methoxyfenozide via hydrogen bonding with a high pesticide loading content of 32.66%. The combination of the methoxyfenozide/SPc complex at a mass ratio of 1:1 could break the self-aggregated methoxyfenozide, reducing its particle size from 1084 to 27 nm, and the methoxyfenozide/SPc complex consisted of smooth spherical nanoparticles with uniform distribution. Importantly, with the aid of SPc, the mortality of methoxyfenozide-treated Spodoptera litura larvae was significantly increased by 1.2 times at 1 day and 2.2 times at 7 days after the oral feeding. Meanwhile, the weight and length of the survival larvae fed with the methoxyfenozide/SPc complex were less than those with methoxyfenozide alone. Transcriptome results revealed that the oral feeding of the methoxyfenozide/SPc complex could further disturb the expression of various key genes related to insect hormone synthesis and metabolism, hormone receptor, and cuticle biosynthesis. In larvae exposed to the methoxyfenozide/SPc complex, we observed the downregulation of key genes involved in hormone synthesis and metabolism, including cytochrome P450 18a, farnesol dehydrogenase, and juvenile hormone acid O-methyltransferase. This disruption in hormone regulation resulted in impaired insect molting. Simultaneously, the expression of genes associated with cuticle formation, such as chitin synthase 2, obstructor-E, and larval cuticle protein, was also suppressed. The current study provides an efficient nano-delivery system for IGRs to improve stomach toxicity against insect pests, which shows great potential in green pest management.