Foliar Application of dsRNA to Induce Gene Silencing in Emerald Ash Borer: Systemic Distribution, Persistence, and Bioactivity †

RNA interference (RNAi) is a cellular mechanism triggered by double-stranded RNA (dsRNA), in which gene expression is reduced in a sequence-specific manner, allowing development of pest-specific control strategies. Effective delivery of the dsRNA is a hurdle, particularly in systems with endophagous insects such as the emerald ash borer (EAB) Agrilus planipennis, an invasive phloem-feeding beetle that develops beneath the bark of ash trees, Fraxinus spp., causing rapid tree death. We evaluated uptake and bioactivity of dsRNA in green ash (F. pennsylvanica) growing in a greenhouse to investigate the feasibility of delivery through the host plant. To assess dsRNA persistence and distribution, seedlings were exposed to EAB-specific dsRNA using foliar spray and sectioned into different tissue types at selected time-points; RT-PCR and Sanger sequencing were used to detect the exogenous dsRNA. We found dsRNA persistence in plant tissues 21 days after treatment. To evaluate bioactivity, neonate EAB were exposed to treated seedlings and assessed for gene expression and feeding behavior. Results demonstrate gene silencing and a 24% (p = 0.03) reduction in cambial consumption. Our findings provide proof-of-concept for delivery of RNAi to the target insect through the host plant, suggesting the feasibility of RNAi functioning as a sustainable approach for tree protection against EAB.