"Buzz buzz buzz", next time you hear the sound of a mosquito, remember to slap it hard!

Mosquitoes appeared on Earth hundreds of millions of years ago. Currently, there are more than 3,500 species of mosquitoes widely distributed in tropical and temperate regions.

Although there are many types of mosquitoes, the good news is that only a few species of female mosquitoes suck blood. All male mosquitoes and most species of female mosquitoes only feed on nectar, juice and plant secretions. But the bad news is that these blood-sucking mosquitoes may also transmit diseases to you while sucking blood.

Mosquitoes sucking blood (Source: BBC News)

Because they suck blood from different organisms, female mosquitoes have become vectors for some major infectious diseases, such as malaria, Zika, yellow fever, dengue fever, West Nile disease and other viruses. Once bitten, there is a risk of infection . Even if you are not infected, the "saliva" injected by mosquitoes when biting makes us feel itchy.

Dengue fever is transmitted by mosquitoes. Image source: BBC News

So, in our daily lives, what can we do to avoid mosquito bites?

Make mosquitoes unable to bite

When we smell the aroma of food on the road, it is easy to find the restaurant by following the source of the scent. The same is true for mosquitoes. They can accurately find our location by following wisps of carbon dioxide, heat and sweat emitted from the body surface, and then launch an attack.

For a long time, humans have mostly used chemical means such as mosquito repellents to fight mosquitoes, which cover up the factors that attract mosquitoes and make them avoid us. However, some people are worried that the chemical components in them will have an impact on human health and the environment. For this reason, Robert Hurt, a chemical engineer at Brown University in the United States, proposed a physical method of mosquito repellent: using graphene composed of a single layer of carbon atoms.

Image source: Wikipedia

The ultra-thin, ultra-light and conductive properties of graphene films make them a popular component of wearable fabrics and skin technologies. Existing studies have shown that wearables incorporating graphene materials can be used for a variety of purposes, including biological monitoring, sensors, UV protection, chemical defense, etc.

Hurt noticed the completely dense two-dimensional structure of graphene film, and he thought that this material could block the odor of arm sweat and prevent the insertion of mosquito mouthparts. So he designed an experiment to "feed" mosquitoes, and the subjects were Hurt's team.

In laboratory tests, skin covered with graphene film was not attacked by mosquitoes. Image source: Hurt Lab and Brown University

They first put their unprotected arms into a box full of mosquitoes, which undoubtedly drove the mosquitoes crazy, and they scrambled to land on the arms and bite them up and down. Then, they put the graphene sheet on the arms and put them in the box. The mosquitoes did not show much interest at this time. Even if a few mosquitoes landed on the arms, they left without interest after trying to bite them in vain.

Mosquitoes gather on the arm to bite without protection

Image source: Research paper with attached pictures

This experiment shows that graphene can block the smell emitted from the skin surface, making it undetectable to mosquitoes, and the structural characteristics also prevent mosquitoes from inserting their mouthparts into the skin. However, it is worth noting that this defense function is only effective when the graphene sheet is in a dry state. In other words, if a large amount of sweat is produced on the surface of the body, the graphene sheet will absorb water and swell, giving mosquitoes an opportunity to take advantage.

Mosquitoes will really be scared if you slap them!

"Buzz buzz buzz", when a mosquito flies around us, we always can't help but reach out to slap it.

However, in most cases it is difficult for us to hit them, and we can only be annoyed by our own slow movements and the mosquitoes' quick dodge ability. But even if one attack fails, we can add multiple attacks, because this is actually an effective way to repel mosquitoes.

For mosquitoes, humans are both a source of food and a source of death. Mosquitoes know this very well. Therefore, when they encounter defensive behaviors such as flapping and trembling of the bitten person, they will associate the smell information of the defensive individual and will not attack the creature carrying the smell for a period of time (up to about a day). Instead, they will avoid it as if it were a "plague god".

Image source: Google Images

This actually takes advantage of the mosquito's preference learning, because mosquitoes are actually picky eaters. For example, the spotted Aedes aegypti's favorite food is human blood, but if it really can't bite humans, it will occasionally attack dogs, cows and other animals. However, once they have the opportunity to bite humans, they will turn their attention back to humans. This is a preference formed by mosquitoes' long-term learning.

But we can also use this learning in reverse. In most insects, dopamine is essential for learning ability, which helps them remember positive and negative feedback. When mosquitoes suck human blood, dopamine gives positive feedback, which makes mosquitoes like the taste; but if the mosquito is attacked during the feeding process, dopamine will give negative feedback, which will make the mosquito disgusted.

It's like when you are eating, and suddenly the coriander in the bowl jumps up and slaps you in the face. This will leave such a great shock in your young mind that you don't want to see coriander again for a short or even long time.

In addition, if you are "unlucky" enough to hit a mosquito and let its blood splatter on the spot, it can even serve as a "killing the chicken to scare the monkey", because mosquitoes will also be scared when they encounter their dead companions.

Mosquito eradication should start from childhood

The most vulnerable stage in a mosquito's life is its infancy. Mosquito larvae, called "mosquito larvae", mainly live in water. At this time, the larvae have not yet developed "fangs" and have weak mobility, so they become prey to many insects.

For example, dragonflies and damselflies like to eat mosquitoes very much. Not only do they like to eat mosquito larvae in the water when they are young, but they also like to prey on adult mosquitoes when they grow up. Moreover, dragonflies are much faster than mosquitoes and can easily catch adult mosquitoes. They are well-deserved "mosquito killer masters".

Damselfly preying on mosquitoes (Source: mosquitonix)

It's a pity that although these insects are extremely lethal to mosquitoes, they cannot be specially raised. However, we can change our thinking. For example, before the mosquito egg-laying season arrives, we can clean up the places where water accumulates inside and outside the house, and do not leave water sources for mosquitoes to create opportunities for reproduction. In this way, at least there will be fewer mosquitoes appearing in the home.

References:

1.Mosquito bite prevention through graphene barrier layers

https://www.pnas.org/doi/10.1073/pnas.1906612116

2.Modulation of Host Learning in Aedes aegypti Mosquitoes

3.https://www.cell.com/current-biology/fulltext/S0960-9822(17)31617-2

4.Insect Olfaction: Once Swatted, Twice Shy

https://www.cell.com/current-biology/fulltext/S0960-9822(17)31722-0

Author: Fish

Winner of the Silver Award for Outstanding Science Popularization Works of China Science Writers Association

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