Assessing nanoparticle-enabled dsRNA delivery for oral RNAi in two orthopteran pests: Schistocerca gregaria and Melanoplus sanguinipes

Abstract

Locusts and pest grasshoppers (Orthoptera: Acrididae) cause significant economic losses to agricultural crops and rangeland forage and can even cause humanitarian crises during periodic plagues. Current management methods for these insects rely heavily on broad-spectrum chemical insecticides and growth regulators, which can affect non-target organisms and may eventually develop resistance in the targeted species. Therefore, we assessed the potential of RNA interference (RNAi)-based alternative strategies that could supplement the current management methods. In insects, RNAi efficiency is known to vary with the method of double-stranded RNA (dsRNA) delivery. In this study, we tested two different delivery methods (injection and oral feeding) in the desert locust (Schistocerca gregaria) and the migratory grasshopper (Melanoplus sanguinipes) and showed that both species are sensitive to the injection but not to the oral feeding of dsRNA, likely due to high nuclease activity or poor uptake in the midgut. To address these limitations, we explored the utility of using nanoparticles that are often used for drug delivery in humans as a carrier (poly lactic-co-glycolic acid [PLGA] and poly(L-arginine)-polyethylene glycol [PLA-PEG]) for orally delivering dsRNA to the insect pests. Although the PLGA nanoparticles successfully permeated the digestive system into the hemolymph and the PLA-PEG-dsRNA complexes remained stable in the midgut juice and were detected in the fat body, neither dsRNA-encapsulating nanoparticle elicited gene knockdown upon oral feeding. These results suggest that nanoparticle-based oral delivery improves dsRNA stability and midgut permeation. However, additional barriers must be overcome to achieve efficient oral RNAi in these orthopteran pest species.