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 control strategies with a narrow spectrum of activity. Consequently, RNA-based biopesticides are emerging as a new technology for insect management. Effective delivery of the dsRNA is a hurdle, particularly in systems with endophagous insects such as the emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae), an invasive forest pest that develops and feeds beneath the bark of ash trees, Fraxinus spp., causing rapid tree death. We evaluated uptake and bioactivity of dsRNA in green ash (F. pennsylvanica) 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, followed by sectioning into different tissue types at selected time-points. RT-PCR and Sanger Sequencing were used to assess dsRNA recovery for each tissue type and time point. We found persistence of dsRNA in plant tissues 21 days after treatment. To evaluate bioactivity, neonate EABs were exposed to treated seedlings and assessed for gene expression and feeding behavior by measuring the gallery area on the debarked seedlings. Results demonstrate gene silencing and a 24% (p=0.03) reduction in cambial consumption in treated seedlings. This study provides foundational 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.
