pH-responsive HACCs co-delivery of dsRNA and cyenopyrafen synergistically controls Tetranychus urticae and...

Developing biopesticides and reducing dependency on chemical acaricides are imperative for sustainable agriculture. Herein, a nano-delivery system (Cpf@CHC-dsRNA/HACCs) based on chitosan quaternary ammonium salt (HACCs) was developed for the co-delivery of dsRNA targeting CHS, CnCC, and HR96 genes, along with the acaricide cyenopyrafen (Cpf). Scanning electron microscopy images showed that the nanoparticles exhibited a regular polyhedral morphology with an average size of approximately 500 nm, demonstrating good stability and pH-responsive release behavior. At pH 5.0, the cumulative release rate of Cpf reached 97.0 ± 1.1% within 204 h. Toxicity bioassay revealed that the LC₅₀ values of Cpf@CHC-dsRNA/HACCs against Tetranychus urticae and Tetranychus truncatus were 15.431 μg/mL and 0.413 μg/mL, respectively, which were significantly lower than those of Cpf, Cpf@Stpp/HACCs, and CHC-dsRNA/HACCs. qPCR and histopathological analysis further demonstrated that target gene suppression by Cpf@CHC-dsRNA/HACCs correlated with developmental deformities and tissue damage in spider mites, resulting in enhanced acaricidal efficacy. The formulation exhibited good biocompatibility on cotton, with lower acute toxicity to the beneficial organisms Anystis baccarum (LC₅₀ = 185.537 μg/cm²) and Eisenia fetida (LC₅₀ = 81.027 μg/cm²) compared to technical Cpf. Fluorescence tracing confirmed its efficient penetration and accumulation in both plant tissues and spider mite bodies. Therefore, Cpf@CHC-dsRNA/HACCs significantly enhance spider mite susceptibility to Cpf through effective silencing of CHS, CnCC, and HR96 genes, offering a promising nano-delivery strategy for reducing pesticide usage while improving efficacy.