Why mosquitoes decide to prey on your feet and arms versus the similarly exposed human sitting next to you is a question science has yet to definitively answer. But thanks to new data we may be one step closer.
Data: Mosquitoes' Sense of Smell Appears to Be Stronger Than Their Sight
To test how mosquitoes might follow a trail of CO2 to their food, researchers focused on Aedes aegypti, a species that is sometimes called the yellow fever mosquito and that can also transmit dengue fever and other viruses, according to the World Health Organization.
Researchers collected data from approximately 250 female mosquitoes (male mosquitoes do not feed on blood), tracking their behavior and recording in real time the mosquitoes' brains during a series of experiments conducted in a cylindrical arena about 7 inches in diameter. The scientists were able to measure the mosquitoesâ€™ wing movements (using a special type of optical sensor) in response to different odors and visual stimuli.
One-second puffs of air containing 5 percent CO2 â€” human exhalations are typically 4.5 percent CO2 â€” prompted the mosquitoes to beat their wings faster.
The mosquitoes also beat their wings faster in response to the visual cue of a bar moving horizontally across a screen around the arena. The mosquitoes tried to move in the direction of the moving bar. But increase in wing-beating speed was more pronounced when mosquitoes smelled the puff of CO2 before they saw the moving bar, compared with just seeing the bar move.
The researchers repeated the experiments with a genetically modified strain of the Aedes aegypti mosquito whose central nervous system cells were designed to glow fluorescent green when they are actively firing.
The data revealed regions of the mosquitoesâ€™ brains linked to visual cues lit up (and were active) when the mosquitoes saw the horizontal bar moving during the experiment, as well as when the puff of CO2 was released. The reverse wasnâ€™t true, however. Seeing the bar before smelling CO2 didnâ€™t alter activity in regions of the brain that control smell, Riffell explains. It shows that for these mosquitoes, he says: "Smell triggers vision, but vision does not trigger the sense of smell."
Data May Help Mosquito Control in the Future, but More Research Is Needed
The results offer new insight into how mosquitoes compensate for having relatively poor eyesight, and itâ€™s possible that more research might one day yield new methods of mosquito control (and therefore lowering the spread of mosquito-borne disease), says Antoine Cribellier, a PhD candidate researching mosquito flight at the University of Wageningen in the Netherlands who wasnâ€™t involved in the study.
To repel mosquitoes, itâ€™s necessary to either mask the scent from the hosts (you and me) that attracts the insects to begin with, or to interfere with mosquitoesâ€™ sensory systems, explains Joseph Conlon, a technical adviser for the American Mosquito Control Association, who was not involved in the new research.
â€œI donâ€™t necessarily find any earthshaking data [from this research] that should influence personal protective measures.â€
What experts do recommend to avoid mosquito bites is:
- Cover arms, legs, and other exposed skin
- Use insect repellents
- Stay indoors at dawn and dusk (when mosquitoes tend to be most active)
- Use a fan or find an area that is breezy (mosquitoes are weak fliers; a little airflow can help keep them away)
One limitation of the study is that mosquitoes were tethered in a controlled environment in a lab, and itâ€™s possible their flight responses might be different in the open air. Also, the Aedes aegypti is a species of mosquito that is active during the day, and itâ€™s possible results might differ for mosquitoes that come out at night, Conlon notes.
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