Abstract
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.
Highlights
RNA interference (RNAi) is a mechanism of gene silencing present in most eukaryote organism to regulate gene expression (Hannon, 2002)
In order to assess whether double-stranded RNA (dsRNA)-based pesticide sprays adversely affect valued non-target species in the agroecosystem, three questions need to be addressed: (1) Are the non-target arthropods exposed to biologically active dsRNA? (2) Do the non-target arthropods possess the RNAi machinery for dsRNA to trigger a response? and (3) are there sufficient sequence matches between the dsRNA molecule under consideration and the genome of the non-target arthropods to cause a sequencespecific effect
While it is possible to make some generalizations regarding the level of exposure, potential uptake of dsRNA and the sensitivity to dietary RNAi for common non-target species in field crops, some open questions remain
Summary
RNA interference (RNAi) is a mechanism of gene silencing present in most eukaryote organism to regulate gene expression (Hannon, 2002). RNAi provides a tool that can be designed to affect and control insect pests in a highly specific manner by targeting genes that are essential for the survival of the species (Xue et al, 2012; Burand and Hunter, 2013; Zhang et al, 2017; Liu et al, 2020). For application as a pest control tool, the active dsRNA molecule has to enter and affect the target pest. This can be achieved by two main ways of application. The first product of that kind has recently been approved by US regulators in June 20171 This particular GE maize event (MON87411) produces a dsRNA targeting the Snf protein in the Western Corn Rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae), which is crucial for the transport of transmembrane proteins. The dsRNA molecules can be applied externally, for example in irrigation water or through trunk injections (Hunter et al, 2012; Li et al, 2015a; Niu et al, 2018; Kunte et al, 2020), in food-baits (Zhou et al, 2008; Zhang et al, 2010), by using delivery systems such as micro-organisms, viruses, nanocarriers (Kunte et al, 2020; Vogel et al, 2019), or topically as spray applications (San Miguel and Scott, 2016)
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