To many, mosquitos are the bane of human existence. Aside from the itchy bites that they leave on our skin after feasting on our blood, mosquitos are also effective transmitters of serious, sometimes fatal diseases like dengue fever, yellow fever, malaria, and Zika. The fate of mosquitos relies on the nutrients and proteins in blood which are essential for egg production. As a result, female mosquitos need to be extremely adept at seeking out human hosts for a blood meal.

The natural driving impulse of mosquitos to host seek is inextricably tied to how they sense and process different cues that uniquely emanate from humans, such as olfactory cues, visual cues, temperature, and moisture. In a recent study, Raji et al. showcase how odor plays a key role in aiding the Aedes aegypti mosquito to seek out human hosts. The researchers found that an antenna-specific ionotropic odor receptor, Ir8a, is sensitive to acidic volatiles present in human sweat. These volatiles, like lactic acid and carboxylic acids, are known to actively drive a mosquito’s attraction to humans. By mutating the Ir8a gene and evaluating the mosquitos’ behavioral and electrophysiological responses when exposed to a panel of volatile odors and human subjects, the research group observed that mosquitos bearing the mutant receptor lost attraction to the odor source. Even when researchers further isolated human odor to just a nylon sleeve, they noted that mosquitos with mutant Ir8a exhibited defective host-seeking behavior compared to mosquitos bearing the Ir8a wildtype receptor.

This study identifies the Ir8a pathway as an important way that mosquitos use odor to distinguish and seek out human hosts. There are, however, many other host cues such has CO₂ and heat that influence a mosquito’s complex attraction to humans as well as its feeding behavior. CO₂ activation, in particular, prevails as the primary gate through which other sensory pathways, Ir8a-mediated odor sensing included, are integrated by mosquitos. By understanding how mosquitos combine and process different sensory cues, the development of more effective methods to prevent them from targeting human hosts can be achieved.

Raji, J. I. et al. Aedes aegypti Mosquitoes Detect Acidic Volatiles Found in Human Odor Using the IR8a Pathway. Curr. Biol. (2019). doi:https://doi.org/10.1016/j.cub.2019.02.045

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