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This picture shows a mosquito brain, highlighting the presence of dopamine in regions involved in the sense of smell. The purple areas indicate tyrosine hydroxylase, which is the precursor of dopamine. Photo: Gabriella Wolff/Virginia Tech

A new study from researchers at Virginia Tech found that swatting does actually help keep pesky mosquitoes away, no matter how tempting your sweet scent is to them.

Researchers determined that mosquitoes can learn and remember the smells of various hosts – and that dopamine plays a major role in this process.

Previous research has shown that different species of mosquitoes exhibit preferences for host species, but will shift to less-preferred hosts if their ideal source is not available. Mosquitoes also show an even more selective preference for individuals within a host population, which is why certain humans seem to attract mosquitoes more than others.

But hosts serve as both prey and predator for mosquitoes, the researchers report. A host’s defensive behaviors are a major source of mortality for adult female mosquitoes, so the team conducted an experiment to examine the ability of mosquitoes to learn the association between host odors and aversive stimuli.

Researchers placed female Aedes aegypti mosquitoes in an insect flight simulator and exposed them to various smells, including human body odors, as well as neutral control odors and observed which scents they were most attracted to. As expected, human odors were attractive to the mosquitoes.

The mosquitoes were then trained to associate specific scents, such as human body odors, with unpleasant shocks and vibrations that mimic swatting. To find out if the mosquitoes would avoid human scents after having negative experiences with the shocks and vibrations, the team put the mosquitoes in an insect flight simulator 24 hours after training. The mosquitoes were again exposed to various smells – including the body odors of 10 individual human subjects (five male, five female). In the Y-shaped maze, the mosquitoes flew upwind and would choose between a control odor and the previously-preferred human odor.

After being trained, the smell of human odor associated with the vibrations was as big a deterrent as 40 percent DEET insect repellent was on untrained mosquitoes.

However, untrained mosquitoes put into the same flight simulator were strongly attracted to the human body odors.

A second, similar experiment was done, but this time using rat and chicken body odors. A group of mosquitoes was trained to avoid the rat odor, and was tested in the flight simulator 24 hours later. While untrained mosquitoes were equally attracted to the scents of both the rat and chicken, the trained mosquitoes significantly avoided the rats and flew toward the chicken odor. The findings demonstrate that mosquitoes exhibit a trait known as aversive learning.

While the mosquitoes were in the flight simulator, the researchers recorded the insects’ neural activity and found that dopamine is a key mediator of aversive learning for the species.

“Our results show that dopamine is necessary for aversive learning in mosquitoes and plays an important role in modulating olfactory responses, allowing for an increased ability to discriminate between odors and hosts,” the study authors wrote.

The researchers did note that there is now way to know what specific factors attract mosquitoes to an individual human, since we are made of up of “unique molecular cocktails” that include combinations of more than 400 chemicals.

"However, we now know that mosquitoes are able to learn odors emitted by their host and avoid those that were more defensive,” said Chloé Lahondère, research assistant professor in the Department of Biochemistry.

Having a better understanding of mosquito learning and preferences for hosts may offer new insight into more efficient methods of mosquito control, according to Lahondère.

Researchers used an insect flight simulator (pictured here) along with CRISPR gene editing and RNAi techniques to determine that dopamine is a key mediator of aversive learning in mosquitoes. Photo: Kiley Riffell
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