Risk Assessment of RNAi-Based Potential Pesticide dsNlAtg3 and Its Homologues for Nilaparvata lugens and Non-Target Organisms

The brown planthopper (Nilaparvata lugens) is an insect pest of rice, which mainly feeds on the phloem sap of the leaf sheath. RNA interference (RNAi) has application prospects in pest control, but it is necessary to select target genes and design suitable dsRNA fragments for RNAi so that it can achieve effective pest control and avoid risks to non-target organisms. NlAtg3 is a key protein in the autophagy pathway of N. lugens. Three kinds of dsRNA fragments of the NlAtg3 gene (dsNlAtg3-474&times:1, dsNlAtg3-138&times:3 and dsNlAtg3-47&times:10) were designed to compare the RNAi efficiency and specificity against the target insect N. lugens and non-target organisms through microinjection. The results showed that the fragment dsNlAtg3-474&times:1 showed strong inhibitory effects on the survival of N. lugens, which resulted in the survival rate decreasing to zero on the fifth day, while the survival rate of a closely related species, Sogatella furcifera, dropped to 2.22%. In contrast, dsNlAtg3-47&times:10 specifically designed against N. lugens only showed slight or no inhibitory effects on S. furcifera and other non-target organisms such as Drosophila melanogaster, but still showed good lethal effects against N. lugens, with the survival rate dropping to 18.89% on the ninth day. In addition, after being fed N. lugens injected with dsNlAtg3-47&times:10 fragments, the survival rate of the natural enemies Dolomedes sulfureus and Tytthus chinensis did not show significant change, compared with those treated with the dsGFP control. Our results suggest that the NlAtg3 gene can serve as a potential target for controlling N. lugens. Moreover, by designing suitable RNAi fragments, it is possible to avoid harm to non-target organisms while effectively inhibiting the target insect N. lugens.