Poly-l-lysine functionalized melanin nanocarrier boosts dsRNA delivery and RNAi efficiency in the migratory locust

RNA interference (RNAi)-based biopesticides, recognized by Science as one of the top ten scientific breakthroughs of 2024, are poised to drive the third revolution in pesticide development. However, the practical applications of RNAi face critical challenges, particularly in overcoming delivery barriers, such as double-stranded RNA (dsRNA) degradation and poor cellular uptake. In this study, we developed a biologically derived melanin nanoparticles (MNP) functionalized with poly- l -lysine (PLL) to deliver dsRNA in Locusta migratoria , a major agricultural pest. The functionalized melanin nanoparticles (MNP-PLL) self-assemble with dsRNA to form MNP-PLL/dsRNA through electrostatic interactions. We evaluated their stability under different environmental conditions, such as in midgut fluid, under various temperature and UV irradiation, demonstrating significantly enhanced resistance to degradation. Bioassays showed substantial improvements in RNAi efficiency and insect mortality. Using fluorescent labeling and pharmacological inhibitors, we further investigated the cellular uptake mechanisms. In contrast to naked dsRNA, chitosan/dsRNA, carbon quantum dots/dsRNA and Spc/dsRNA, MNP-PLL/dsRNA activated three distinct endocytic pathways: clathrin-mediated endocytosis, caveolin-mediated endocytosis, and macropinocytosis, facilitating efficient cellular internalization. Acute toxicity assays confirmed excellent biocompatibility and safety of MNP-PLL to the Western honey bee and zebrafish. This study represents the first application of PLL-functionalized melanin as an efficient nanocarrier to generate MNP-PLL/dsRNA for agricultural pest control, highlighting their strong potential as a next-generation dsRNA delivery platform for sustainable pest management.