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Mosquitoes Remember the Smell of People Who Swat Them

Photo by: Enrique Dans via Flickr


For people living in the tropics where mosquitoes abound, it may be sometimes frustrating to attempt to kill potential malaria or dengue carriers by swatting the insect then missing it. However, a new study said that the swat attempts are not lost.

The mosquito remembers the smell of the person who tried to swat it and will eventually avoid the person, researchers at Virginia Tech said. Dopamine is a key mediator of the process, Science Daily reported.


Preference for a Particular Host

The study, published in the Current Biology journal, said that mosquitoes can learn rapidly and remember the smells of their hosts. The insect will then use this information and incorporate it with other stimuli to develop preferences for a specific vertebrae host species.



According to Clement Vinauger, an assistant professor of biochemistry at the College of Agriculture and Life Sciences of Virginia Tech, and Chloe Lahondere, a research assistant professor at the Department of Biochemistry, mosquitoes show aversive learning -- a trait. They demonstrated the trait by training female Aedes aegypti mosquitoes to associate odors, including human smell, with unpleasant vibrations and shocks.

Using a Y-maze olfactometer after one day, the researchers assessed the same mosquitoes. The insects had to fly upwind and choose between a human body odor – that they once preferred – and a control odor. When the mosquitoes avoided the human body odor, it indicated that they had been trained successfully.


Averse Learning in Mosquitoes

The researchers used cutting-edge technology, such as CRISPR gene editing and RNAi, and took a multidisciplinary approach to identify that dopamine is a key mediator of aversive learning in mosquitoes.  They fitted the mosquitoes with helmets to target specific parts of the insect’s brains involved in olfactory integration. The helmets recorded and observed brain activity.

They also placed the mosquitoes in an insect flight simulator and exposed the insect to different smells, including human body odors to observe insect reaction. The researchers observed that the neural activity in the brain region where olfactory information is processed was modulated by dopamine. The modulation was done in such a way that it was easier for the insects to discriminate and potentially learn the odors.

However, Lahondere said that there is, unfortunately, no way of knowing what exactly attracts a mosquito to a particular person. She explained that humans are made up of unique molecular cocktails that include combinations of more than 400 chemicals. But Lahondere said that mosquitoes are able to learn odors emitted by their hosts and avoid those that were previously defensive.


New Tools for Mosquito Controls

Lahondere said that by understanding these mechanisms of mosquito learning and preferences, it may provide science with new tools for mosquito control. She said that the ability of mosquitoes to learn can be targeted to impair or exploit it to humans’ advantage.



Besides malaria and dengue, mosquitoes are also carriers of the Zika virus, chikungunya, and yellow fever virus which can be fatal with just one bite.

Gizmodo pointed out that female mosquitoes have a highly sensitive nose made up of an antennae, proboscis, and palp, which is a pair of mouth appendages. There are some species that have a second nose designed specifically to smell out people.

Some research even suggested that mosquitoes are attracted especially to human hosts infected with malaria. The insects could hone in on the desired target because of highly specialized odor sensors that can discern among thousands of different aromatic compounds.


Mosquito Preferences Can Be Learned

Another research by University of Washington scientists, published in the Current Biology journal, studied if the preferences of the mosquitoes can be learned. The team, led by Jeffrey Riffell, used a vortexer, a machine, in an experiment with mosquitoes, rats, and chickens.

The researchers exposed the mosquitoes to a mechanical shock that stimulated the feeling of being near a hand that is making a swat in the air. The insects were trained to associate the smell of the simulated swat with the small of rodents and chicken. The mosquitoes stayed away from the mice in subsequent tests, but the insect remained attracted to chicken even if it was associated with the smell of the simulated human swat.

The team also tried to prove that dopamine is behind it. They produced genetically modified mosquitoes that did not have dopamine receptors. The mutated mosquitoes were glued to a 3D-printed rack and then exposed to various scents. Because the insects were unable to fly, the researchers were able to record their brain activity by measuring the activity of neurons in the olfactory sensors of the mosquitoes’ brain.



Because the mosquitoes are unable to process dopamine, its neurons were less likely to fire. It suggested that mosquitoes without dopamine receptors are less capable of processing and learning from odors.

Riffell said that the mosquitoes will avoid the swatter for 24 hours. However, if there is another person in the room, they will attempt to bite the person. After one day, the insect will forget what it has learned and could lose its life eventually, KPBS noted.

[메디컬리포트=Vittorio Hernandez 기자]

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