Heat and humidity sensors that alert mosquitoes to nearby human hosts

Mosquito-borne diseases sicken >500,000,000 people annually, killing >500,000 1 . Mosquito host-seeking is guided by multiple host-associated cues, which combine to drive blood feeding in a manner that remains poorly understood 2,3 . While heat is a powerful mosquito attractant, recent studies indicate that disruption of heat seeking has little impact on host detection by the malaria vector Anopheles gambiae 4 , suggesting other cues act alongside heat in the complex sensory environment of a human host. Here we show mosquitoes require Ir93a (an Ionotropic Receptor 5 ) to maintain attraction to a human host and feed on warmed blood. Using Ir93a , we uncover the previously uncharacterized mosquito hygrosensory system, and show Ir93a is required for humidity detection by humidity sensors (hygrosensors) as well as temperature detection by thermosensors, and for attraction to each stimulus. These findings indicate that hygrosensation and thermosensation function in parallel, driving host proximity detection in response to the overlapping heat and humidity gradients humans produce 6,7 . These host cue sensors appear to have arisen by co-opting existing sensors of physical cues rather than de novo , as Ir93a -dependent thermo- and hygro-sensors support physiological homeostasis in non-blood-feeding insects 8–11 . While Ir93a is conserved among arthropods, reliance on heat and humidity evolved independently in multiple blood-feeding lineages, suggesting multiple, vector-specific implementations of this common host-seeking strategy.