miR-34-5p , a novel molecular target against lepidopteran pests

The management of economically important lepidopteran pests has relied heavily on chemical and Bt-bio pesticides since 1940s, which has led to multiple recurring issues in resistance and environment. In this study, to search for a genetic-based control alternative with a distinctively different mode of action, we carried out a toxicological characterization of miR-34-5p , a highly conserved lepidopteran microRNA targeting EcR . Integrating target site prediction, co-localization of miRNA and EcR by fluorescence in situ hybridization, luciferase reporter assays as well as the gain-of-function and loss-of-function experiments, we comprehensively examined the physiological function and insecticidal properties of miR-34-5p among three representative lepidopteran pests, including Helicoverpa armigera , Spodoptera exigua, and Plutella xylostella . The combined results confirm a conserved role of miR-34-5p in the regulation of EcR in multiple lepidopteran pests. Overexpression or knocking down of miR-34-5p through both injection and feeding leads to insecticidal phenotypes, including high mortality, low fecundity, and developmental defects, suggesting that miRNAs can be considered as novel molecular targets in general, miR-34-5p for lepidopteran pests in particular. These results highlight the importance of miR-34-5p in the regulation of EcR expression in lepidopteran insects and provide a solid foundation for development of miRNA-based green pest control technology.