Mosquitoes have no mercy on you? Thanks to scientists we know why
Female mosquitoes get on our nerves especially during spring and summer when they are most active. Every year we complain about stings, itchy blisters and discomfort owing to their aggressiveness. Are you notoriously prey to these little insects? Scientists have discovered the reason.
For more than 100 million years, female mosquitoes have been giving a hard time to warm-blooded animals. Scientists have discovered about 3 500 different species of these small and annoying insects. Researchers decided to find out why they attack some people with greater intensity.
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Mosquito threats
Out of more than 3 000 mosquito species several hundred attack humans. Some of them (especially in intertropical regions) carry dangerous pathogens. These include:
- chikungunya viruses
- dengue viruses,
- Japanese yellow fever encephalitis,
- West Nile fever,
- zika,
- malaria.
So it's far more than just small, itchy and annoying stings.
Mosquitoes - how do they hunt us?
Gazeta Wyborcza reports that, female mosquitoes always hunt in the same way: they "hear us" by intercepting the vibrations of the air with the help of rows of hairs located on the feelers. It is worth emphasising, however, that above all, they smell us and pick up odours. What they are looking for is the sour odour of carbon dioxide. To them, it signifies a live and full-blooded animal.
Hunting us down they fly in zigzags, trying to track down the source of the enticing scent. When they are close, they fall into a cloud of odourants that escape our skin. Then they sense the rising heat, and when they land on us, a palette of flavours floats before them. They taste us with nerve receptors located on their limbs.
Mosquitoes and their preferences
It is a well-known fact that mosquitoes prefer to bite some people more than others. Why? In 2022, researchers showed that mosquitoes are attracted to people whose skin produces more sebum. This begs the question: is the insect's target only fat, or the odours associated with it?
As we read in Gazeta Wyborcza, it is probably the latter, because it is known from other studies that mosquitoes dislike some scents (e.g., vervicacea or catnip) and like others (e.g., some soaps).
The odours are most often not our own body aromas, but metabolites released by micro-organisms that live on human skin and feed on sebum. In the latest issue of the journal Current Biology, scientists from the USA and Zambia have demonstrated this.
Researchers have designed an unusual experiment
Before scientists discovered what smells mosquitoes prefer, they set up an experiment. They built a 1,000 square metre research arena in Zambia.
"This is the largest system to assess olfactory preference for any mosquito in the world. And it is a very busy sensory environment for the mosquitoes," said first author of the publication Dr Diego Giraldo of Johns Hopkins University in Baltimore.
As reported by Gazeta Wyborcza, the installation consisted of platforms heated to the temperature of human skin (i.e. 35 degrees centigrade). Between them, the scientists released 200 hungry mosquitoes of the species 'Anopheles gambiae', which in Africa is one of those transmitting malaria. The insects' activity was tracked using infrared cameras. With these, the scientists were able to determine whether the females were landing on heated platforms. This would mean that they are ready to sting.
It turned out that mosquitoes will not attack until they can smell carbon dioxide and other odours. Heat alone is an insufficient indicator that there's a potential prey in front of them.
Mosquitoes and volunteers
The researchers deployed closed tents with six volunteers near the platforms. It turned out that the mosquitoes had once again become picky. They preferred some people to others. In addition, this pattern repeated itself every night - insect attacks on the research platforms occurred most often between 10 pm and 2 am.
The female mosquitoes particularly avoided one of the volunteers, who smelled peculiarly even to other people. The study showed that hungry female mosquitoes 'Anopheles gambiae' chose people who smelled strongly of carboxylic acids. Instead, they avoided the aroma of eucalyptol - a terpene that can be obtained from eucalyptus, rosemary or wormwood, among others.
The volunteer who was avoided by the mosquitoes emitted less carboxylic acids and three times more eucalyptol than the others, as we read in the Gazeta Wyborcza. Why the difference in smell? The authors of the publication speculate that it was due to the specific diet of the 'disliked by mosquitoes' volunteer.
