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 pesticidesinsteadof traditional synthetic pesticides to minimize potential threatsto food and environmental safety. Insect growth regulators (IGRs)are regarded as a secure alternative, but their control efficacy needsto 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 viahydrogen bonding with a high pesticide loading content of 32.66%.The combination of the methoxyfenozide/SPc complex at a mass ratioof 1:1 could break the self-aggregated methoxyfenozide, reducing itsparticle 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 increasedby 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 themethoxyfenozide/SPc complex were less than those with methoxyfenozidealone. Transcriptome results revealed that the oral feeding of themethoxyfenozide/SPc complex could further disturb the expression ofvarious key genes related to insect hormone synthesis and metabolism,hormone receptor, and cuticle biosynthesis. In larvae exposed to themethoxyfenozide/SPc complex, we observed the downregulation of keygenes 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 insectmolting. Simultaneously, the expression of genes associated with cuticleformation, such as chitin synthase 2, obstructor-E, and larval cuticle protein, was also suppressed.The current study provides an efficient nano-delivery system for IGRsto improve stomach toxicity against insect pests, which shows greatpotential in green pest management.