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A globally invasive form of the mosquito Aedes aegypti specializes in biting humans, making it an efficient disease vector1. Host-seeking female mosquitoes strongly prefer human odour over the odour of animals2,3, but exactly how they distinguish between the two is not known. Vertebrate odours are complex blends of volatile chemicals with many shared components4-7, making discrimination an interesting sensory coding challenge. Here we show that human and animal odours evoke activity in distinct combinations of olfactory glomeruli within the Ae. aegypti antennal lobe. One glomerulus in particular is strongly activated by human odour but responds weakly, or not at all, to animal odour. This human-sensitive glomerulus is selectively tuned to the long-chain aldehydes decanal and undecanal, which we show are consistently enriched in human odour and which probably originate from unique human skin lipids. Using synthetic blends, we further demonstrate that signalling in the human-sensitive glomerulus significantly enhances long-range host-seeking behaviour in a wind tunnel, recapitulating preference for human over animal odours. Our research suggests that animal brains may distil complex odour stimuli of innate biological relevance into simple neural codes and reveals targets for the design of next-generation mosquito-control strategies.
The discrimination of odour cues is a challenging problem faced by animals in nature. Decades of olfactory research have revealed the principles by which animals may identify individual compounds or simple mixtures-using combinatorial codes for flexible, learned behaviours8-11 or labelled lines for hard-wired, innate responses12-15. However, most natural odours are blends of tens to hundreds of compounds4,16,17. How animals evolve to efficiently recognize these more complex stimuli, especially those with important innate meaning, is poorly understood18-21.
This problem is particularly relevant for Ae. aegypti mosquitoes, which have recently evolved to specialize in biting humans and therefore become the primary worldwide vectors of human arboviral disease1,22. Female mosquitoes can detect vertebrate animals using the carbon dioxide in breath and other general cues such as body heat, humidity and visual contrast23. However, they rely heavily on body odour for discrimination among species24 and show a robust preference for human odour over the odour of animals2,3 (Fig. 1a-d). The apparent ease with which they distinguish between these stimuli is notable as vertebrate body odours are complex blends of relatively common compounds that are frequently shared across...