A conserved mechanism of cooling detection drives both Drosophila warmth avoidance and Anopheles warmth attraction

Mosquito heat-seeking is driven by an ancestral cooling receptor. Mosquitoes spread diseases that sicken >600 million people and kill >500,000 people annually. To identify hosts on which to blood-feed, female mosquitoes use a multi-sensory approach that includes the detection of odor, carbon dioxide and body heat. Discovery of the mechanisms that underlie odor and carbon dioxide detection in mosquitoes have relied on prior knowledge of the identify of receptors for these cues in Drosophila melanogaster. However, the mechanisms behind heat-seeking have remained elusive. Here, we find that heat-seeking in the malaria mosquito Anopheles gambiae is driven by an ancestral cooling receptor conserved between flies and mosquitoes, the ionotropic receptor (IR) IR21a. We previously showed that Ir21a is required for cooling detection and warm avoidance in Drosophila melanogaster. Here we find that Ir21a also mediates cooling detection in An. gambiae. However, at a behavioral level, Ir21a mediates heat-seeking, rather than avoidance in the mosquito. These results suggest that Ir21a has been functionally repurposed to support blood-feeding behavior in the mosquito. It also suggests that mosquito ”heat-seeking” is driven by cooling avoidance. The discovery of a heat-seeking receptor is of potential utility in combatting against mosquito-borne diseases.