Bacterially Expressed dsRNA Causes Gene Silencing in EAB

RNA interference (RNAi) is a naturally occurring, biological process in which RNA molecules inhibit gene expression or translation by neutralizing target mRNA molecules. Recent advances in our understanding of the RNAi mechanism have allowed its development as an emerging tool to protect against insect pests. The major challenge for efficient pest management using RNAi as a molecular bio-pesticide in the field is development of convenient and efficient methods for production, and practical delivery of stable dsRNAs to the target insect. Our goal is to assess the potential for deploying bacterially produced RNAi as a bio-pesticide against an invasive forest pest, the emerald ash borer (EAB). EAB feeds on the cambial tissue beneath the bark of ash trees (Fraxinus spp.), causing rapid tree death. EAB has killed millions of ash in North America since its discovery in 2002, prompting the need for more innovative management strategies. In our study, bacterial expression and synthesis of dsRNA were performed with E. coli strain HT115 (DE3) using the L4440 expression vector. dsRNA (shi and hsp) over expressed in E. coli was toxic to neonate EAB larvae after oral administration and successfully triggered gene silencing and significant mortality. These results suggest that transformed E. coli expressing dsRNA (shi and hsp) has significant insecticidal activity against EAB and could potentially be used as a novel RNAi based bio-pesticide for management of this invasive forest pest. To our knowledge, this is the first example of an effective RNAi response induced by feeding dsRNA expressing bacteria in a forest pest.