Mineral Oil Encapsulation Enhances dsRNA-Based Acaricidal Activity against Amphitetranychus viennensis

RNA interference (RNAi)-based biopesticides offer precise pest control with minimal environmental impact, yet their field efficacy is limited by rapid degradation of double-stranded RNA (dsRNA) due to UV exposure, nucleases, and poor foliar adhesion. To address these challenges, we developed a mineral oil-based water-in-oil (W/O) emulsion to encapsulate dsRNA targeting the Amphitetranychus viennensis V-ATPase A gene. The formulation was optimized through hydrophilic-lipophilic balance (HLB) screening (optimal HLB = 10), ternary phase ratio adjustment (oil:water:surfactant = 64:20:16), and dsRNA loading concentration tests (optimal: 5000 mg/L). Bioassays assessed toxicity against eggs, nymphs, and adults of Amphitetranychus viennensis, alongside field trials comparing dsRNA@W/O (750× dilution) with naked dsRNA, double-applied naked dsRNA, and the chemical control etoxazole. Key findings demonstrated that dsRNA@W/O significantly enhanced stability: after 72 h of UV/air exposure, 93.67% of activity was retained, compared to complete degradation of naked dsRNA. The formulation accelerated lethality, reducing median lethal time (LT₅₀) from 4.84 to 1.95 days for nymphs and from 4.82 to 2.65 days for adults. Field efficacy at 20 days post-treatment reached 85.75% at 1.33 mg/L dsRNA, outperforming naked dsRNA (62.79%) and approaching etoxazole (95.69%), while using one-third the active ingredient of conventional dsRNA treatments. This work demonstrates a cost-effective, scalable mineral oil encapsulation strategy that synergizes RNAi-mediated pest control with mineral oil's physical effects, offering a sustainable, environmentally safe, and economically feasible pest management approach.