Current Scenario of Exogenously Induced RNAi for Lepidopteran Agricultural Pest Control: From dsRNA Design to Topical Application

Abstract

Invasive insects cost the global economy around USD 70 billion per year. Moreover, increasing agricultural insect pests raise concerns about global food security constraining and infestation rising after climate changes. Current agricultural pest management largely relies on plant breeding-with or without transgenes-and chemical pesticides. Both approaches face serious technological obsolescence in the field due to plant resistance breakdown or development of insecticide resistance. The need for new modes of action (MoA) for managing crop health is growing each year, driven by market demands to reduce economic losses and by consumer demand for phytosanitary measures. The disabling of pest genes through sequence-specific expression silencing is a promising tool in the development of environmentally-friendly and safe biopesticides. The specificity conferred by long dsRNA-base solutions helps minimize effects on off-target genes in the insect pest genome and the target gene in non-target organisms (NTOs). In this review, we summarize the status of gene silencing by RNA interference (RNAi) for agricultural control. More specifically, we focus on the engineering, development and application of gene silencing to control Lepidoptera through non-transforming dsRNA technologies. Despite some delivery and stability drawbacks of topical applications, we reviewed works showing convincing proof-of-concept results that point to innovative solutions. Considerations about the regulation of the ongoing research on dsRNA-based pesticides to produce commercialized products for exogenous application are discussed. Academic and industry initiatives have revealed a worthy effort to control Lepidoptera pests with this new mode of action, which provides more sustainable and reliable technologies for field management. New data on the genomics of this taxon may contribute to a future customized target gene portfolio. As a case study, we illustrate how dsRNA and associated methodologies could be applied to control an important lepidopteran coffee pest.

Keywords: biopesticide; gene target; genome; insect; silencing; topical; validation.

Figure 1

Main taxonomic levels are depicted in a tree, modified from https://lifemap-ncbi.univ-lyon1.fr/ (accessed on 21 September 2022), showing the Insecta class (a), the Ditrysia clade (b) and the Yponomeutoidea superfamily (c). Orange spheres highlight the levels with fully sequenced genome data. Insect species listed in Table 1 and Table 2 (written in white) are marked by a yellow tag. The L. coffeella in the Lyonetiidae family is written in orange.

Figure 2

Schematic strategy of RNAi to control L. coffeella by long dsRNA-induced silencing of coffee plants. (A) dsRNA delivery by SIGS or trunk injection; (B) dsRNA oral ingestion by larva feeding the leaf parenchyma; (C) dsRNA internalization in the larva: a transfer from insect gut lumen to midgut cells by the clathrin-mediated endocytic pathway (CLA), pattern recognition receptors (PRRs), and/or RNA-binding proteins (RBPs); b long dsRNA interaction with an R2D2-DCR2 complex associated with LOQ; c LOQ recognition of exogenously delivered dsRNA to slicing by Dicer (DCR2) with R2D2 to produce siRNAs; d guide-strand selection by AGO2 complexed with C3PO; e siRNA-guided silencing by attachment to the target mRNA passenger strand; systemic amplification of the RNAi silencing by dsRNA and siRNA; f dispersion through other gut cells by the cytoplasm and g diffusion to the hemolymph.