Bioparticle delivery of dsRNA improves insecticidal RNA interference in fall armyworm (Spodoptera frugiperda)

Biopesticides containing double stranded RNA (dsRNA) to initiate an insecticidal gene silencing response by RNA interference (RNAi) represent a very promising pest control strategy recently approved for commercial production. However, RNAi efficacy is hindered in some pests by physiological and cellular barriers against dsRNA, resulting in lower efficacy and limited potency. Lepidopteran insects are refractory to insecticidal RNAi through feeding due to dsRNA degradation in the digestive system, limited cellular uptake, inter- and intracellular transportation, inefficient processing to siRNA, and/or lack of RNA-induced silencing complex formation. Nanoparticle-mediated RNAi delivery is an alternative that may overcome limitations of traditional dsRNA delivery systems. In this study we evaluated minicell-based RNAi biocides for control of fall armyworm (FAW), Spodoptera frugiperda, a devastating lepidopteran pest worldwide. Target FAW genes were identified from dsRNA injection experiments based on the resulting phenotype. Candidate dsRNAs were then designed and encapsulated in nanoparticles (minicells) of various formulations and tested in bioassays against FAW larvae susceptible and resistant to insecticidal proteins from Bacillus thuringiensis. Uptake of minicells in the FAW gut lumen compared to naked dsRNA was monitored using confocal microscopy and GFP-labeled dsRNA. Silencing of target genes was tested using qRT-PCR. Overall, minicell-encapsulated dsRNA improved the efficiency of RNAi in FAW, paving the way for field testing and future development of RNAi biocides against a wide range of pests currently recalcitrant to insecticidal RNAi.