Sensory coding of borneol repellency in culicine mosquitoes via the Or49 pathway

Plant-derived repellents containing borneol and camphor have been used for centuries, yet the sensory mechanisms that mediate their effects in mosquitoes have remained obscure. Here, we show that culicine mosquitoes possess a dedicated olfactory pathway for detecting bicyclic monoterpenoids. We identify odorant receptor 49 (OR49) as a conserved and highly selective borneol receptor expressed in a distinct neuron of the maxillary palp. This neuron forms a defined projection to the MD3 glomerulus in the antennal lobe, establishing a labeled line for plant-derived repellents. Genetic disruption of Or49 abolishes electrophysiological responses to borneol and markedly diminishes avoidance behavior during human host-seeking. These results reveal that female mosquitoes detect borneol through a specialized sensory channel distinct from those mediating attraction to human cues. Our findings provide a mechanistic framework for understanding how plant volatiles shape mosquito behavior and offer a foundation for the rational design of next-generation olfactory repellents.