Erratum. Topically applied AaeIAP1 double-stranded RNA kills female adults of Aedes aegypti. Journal of Medical Entomology 45(3):414–420

Assessing the Risks of Topically Applied dsRNA-Based Products to Non-target Arthropods

RNA interference (RNAi) is a powerful technology that offers new opportunities for pest control through silencing of genes that are essential for the survival of arthropod pests. The approach relies on sequence-specificity of applied double-stranded (ds) RNA that can be designed to have a very narrow spectrum of both the target gene product (RNA) as well as the target organism, and thus allowing highly targeted pest control. Successful RNAi has been reported from a number of arthropod species belonging to various orders. Pest control may be achieved by applying dsRNA as foliar sprays. One of the main concerns related to the use of dsRNA is adverse environmental effects particularly on valued non-target species. Arthropods form an important part of the biodiversity in agricultural landscapes and contribute important ecosystem services. Consequently, environmental risk assessment (ERA) for potential impacts that plant protection products may have on valued non-target arthropods is legally required prior to their placement on the market. We describe how problem formulation can be used to set the context and to develop plausible pathways on how the application of dsRNA-based products could harm valued non-target arthropod species, such as those contributing to biological pest control. The current knowledge regarding the exposure to and the hazard posed by dsRNA in spray products for non-target arthropods is reviewed and suggestions are provided on how to select the most suitable test species and to conduct laboratory-based toxicity studies that provide robust, reliable and interpretable results to support the ERA.

Insecticidal effects of dsRNA targeting the Diap1 gene in dipteran pests

The Drosophila melanogaster (fruit fly) gene Diap1 encodes a protein referred to as DIAP1 (D rosophila Inhibitor of Apoptosis Protein 1) that acts to supress apoptosis in "normal" cells in the fly. In this study we investigate the use of RNA interference (RNAi) to control two dipteran pests, Musca domestica and Delia radicum, by disrupting the control of apoptosis. Larval injections of 125-500 ng of Diap1 dsRNA resulted in dose-dependent mortality which was shown to be attributable to down-regulation of target mRNA. Insects injected with Diap1 dsRNA have approx. 1.5-2-fold higher levels of caspase activity than controls 24 hours post injection, providing biochemical evidence that inhibition of apoptotic activity by the Diap1 gene product has been decreased. By contrast adults were insensitive to injected dsRNA. Oral delivery failed to induce RNAi effects and we suggest this is attributable to degradation of ingested dsRNA by intra and extracellular RNAses. Non-target effects were demonstrated via mortality and down-regulation of Diap1 mRNA levels in M. domestica larvae injected with D. radicum Diap1 dsRNA, despite the absence of 21 bp identical sequence regions in the dsRNA. Here we show that identical 15 bp regions in dsRNA are sufficient to trigger non-target RNAi effects.