RNAi-mediated suppression of embryos as a promising strategy to control Spodoptera littoralis

RNAi for insect control is a promising alternative to synthetic insecticides. Intense research efforts over the years have allowed researchers to develop effective control strategies and, recently, the registration of a new product for the US market. To date, however, the insect stages targeted by RNAi are both juveniles and adults, while the egg stage has been largely ignored, although an early suppression of the pest would more efficiently limit its damage. Here we try to fill this gap by focusing on the silencing of Sl102, a gene that encodes precursors of functional amyloid fibrils involved in the immune response and that, based on literature reports, could have an important role in the modulation of the embryonic development of lepidoptera. We showed that Sl102 is expressed throughout the embryogenesis of Spodoptera littoralis, showing a peak 32 h after oviposition. The transcription level of this gene is strongly reduced by RNAi induced by soaking the eggs in a dsRNA solution. Interestingly, gene silencing is associated with a drastic reduction in egg hatching rate, which is complemented by a very high mortality of the few hatched larvae. Structural and ultrastructural analyses showed a significant delay in the development of silenced embryos, which also exhibited morphological alterations. Our results expand the understanding of the Sl102 gene function, indicating an important role in embryonic development that remains to be studied from a functional point of view. This paves the way toward the future development of effective control strategies for S. littoralis, based on the suppression of embryonic development through RNAi technology.