Human scent guides mosquito thermotaxis and host selection under naturalistic conditions

The African malaria mosquito Anopheles gambiae exhibits a strong innate drive to seek out humans in its sen-sory environment, classically entering homes to land on human skin in the hours flanking midnight. To gain insight into the role that olfactory cues emanating from the human body play in generating this epidemiolog-ically important behavior, we developed a large-scale multi-choice preference assay in Zambia with infrared motion vision under semi-field conditions. We determined that An. gambiae prefers to land on arrayed visual targets warmed to human skin temperature during the nighttime when they are baited with carbon dioxide (CO2) emissions reflective of a large human over background air, body odor from one human over CO2, and the scent of one sleeping human over another. Applying integrative whole body volatilomics to multiple humans tested simultaneously in competition in a six-choice assay, we reveal high attractiveness is associ-ated with whole body odor profiles from humans with increased relative abundances of the volatile carboxylic acids butyric acid, isobutryic acid, and isovaleric acid, and the skin microbe-generated methyl ketone ace-toin. Conversely, those least preferred had whole body odor that was depleted of carboxylic acids among other compounds and enriched with the monoterpenoid eucalyptol. Across expansive spatial scales, heated targets without CO2 or whole body odor were minimally or not attractive at all to An. gambiae. These results indicate that human scent acts critically to guide thermotaxis and host selection by this prolific malaria vector as it navigates towards humans, yielding intrinsic heterogeneity in human biting risk.

Automated summary

The African malaria mosquito Anopheles gambiae has a strong innate drive to seek out humans, particularly in the hours flanking midnight. Through multiple-choice preference assays, it has been determined that An. gambiae is attracted to arrayed visual targets warmed to human skin temperature, carbon dioxide emissions, and specific human body odors. Whole body odor profiles were found to be associated with certain volatile compounds, with higher attractiveness being associated with increased relative abundances of certain carboxylic acids and the skin microbe-generated methyl ketone acetoin. Overall, these findings highlight the critical role of human scent in guiding the behavior of An. gambiae and its selection of host, leading to heterogeneity in human biting risk.