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.