Red appeal

One summer night, the breeze brings a rare coolness. Suddenly, buzzing... Buzz... Buzz... bite! Then there was an irrepressible scratching...

There is no doubt that finding yourself covered in mosquito bites will soon overshadow an otherwise pleasant summer night.

Not only are mosquitoes a nasty thing, they can also transmit diseases such as dengue, yellow fever and Zika virus. Hundreds of millions of people contract these diseases every year, so these "vampires" can also be called one of the deadliest creatures on Earth.

A lot of research on mosquitoes is an effort to understand their behavior and preference for the subject of their bite. Vision is an important sensory for biting insects, including mosquitoes. But they don't rely on sight alone, and the sense of smell and temperature work together with visual cues to help mosquitoes find a host.

A recent study published in the journal Nature Communications explored the appeal of different colours to several mosquitoes capable of transmitting disease, including the Aedes aegypti mosquito, in addition to Anopheles stephensi and Culex quinquefasciatus.

The study found that mosquitoes of different species "taste differently" and tend to have preferences for certain colors (or specific wavelengths) individually, with red, or light with longer wavelengths, being particularly attractive. But in addition to the visual signal, this is also inseparable from the combination of smell.

Prefers red

In fact, there have been many previous studies exploring mosquitoes' preference for color, but the conclusions can be said to be very confusing and even contradictory. Some studies suggest that mosquitoes prefer blue, other experiments suggest that mosquitoes prefer yellow-green, and so on.

This happens because it is not easy to test a mosquito's color preferences, for example, the color an object looks like is not simply equivalent to the wavelength of light it emits. In addition, the results may also be affected by factors such as the brightness and contrast of the light, and there are many variables in such experiments that need to be controlled.

In the new study, the scientists tried a series of more complete tests on three mosquito species. In one experiment, the team used a wind tunnel equipped with a camera to track the mosquito's flight patterns. In this wind tunnel, they can act as naturally as possible.

On the floor of the wind tunnel there are two colored dots, one of which represents the color of interest (i.e. a certain wavelength) and the other as a reference point, white. The researchers took a number of color samples to mimic different skin tones.

Only female mosquitoes bite because for most species, females need blood to complete the reproductive process. As a result, about 50 female mosquitoes that have mated but not eaten at a time are released into the wind tunnel, where they will naturally seek a host.

Then, after about an hour, carbon dioxide (CO) is released into the wind tunnel. This is a gas that humans and other mammals exhale. Although carbon dioxide doesn't smell to us, mosquitoes can smell it and can use this smell to guide them to the source of blood.

After 1.3 million "mosquito flights," the team got the results. Before releasing the odor stimulus, the Aedes aegypti mosquitoes largely ignored the colored dots on the floor and instead explored the ceiling and wind tunnel walls. But once carbon dioxide appeared, they began to explore colored dots on the floor, especially as the wavelength of the dots increased from 510 nanometers to 660 nanometers.

These longer wavelengths represent the orange and reddish ends of the spectrum. Experiments have shown that Aedes aegypti mosquitoes are most interested in red, followed by black. It is worth noting that these orange to red wavelengths are similar to those emitted by human skin tones. Conversely, blue, green, and purple were not less attractive to them than the control group.

When experiments were conducted using highlights of skin tone, they were more attractive to mosquitoes than the control group, but no preference for any particular skin color was observed.

Previous experiments have shown that mosquitoes are more likely to be attracted to contrasting colors, such as the pattern of a checkerboard grid, rather than a single solid color. The researchers also showed the mosquitoes different bright spots in a similar and highly contrasting background, and found that Aedes aegypti mosquitoes were more interested in highlights that had a high contrast with the background. Scientists believe this helps mosquitoes distinguish between objects (people) and backgrounds, even in low-light environments. For mosquitoes, contrast may be more important than the color itself.

Similar to the Aedes aegypti mosquito, Anopheles spp. is also attracted to black and red and has little interest in shorter wavelengths. Tired Culex showed interest in blue-violet and red, interestingly, the poles of the test spectrum.

The researchers also conducted a separate experiment in an insect cage to explore the appeal of real skin tone to mosquitoes. Six volunteers from different ethnic backgrounds were recruited to help with the test.

The control in the experiment was a white glove, which was placed in one window, while the volunteer's hand was placed in another, and the researchers simultaneously watched whether the mosquitoes were attracted to any particular skin color.

Mosquitoes are significantly more attracted to the skin than white gloves, but like bright spots, they don't have a preference for a particular skin color.

What does this mean?

This study suggests that mosquitoes are attracted to the color of human skin, but only in the presence of carbon dioxide, suggesting that the smell of breath in humans or mammals may serve as an initial clue. This result also confirms the previous conclusion that carbon dioxide does attract mosquitoes.

Scientists have found that color and contrast are important factors in the attraction of the Aedes aegypti mosquito. But at the same time, the researchers acknowledge that their experiments have not yet considered some of the other factors that affect mosquitoes' choice of host, including chemicals released by human skin, skin temperature and sweat on the skin. Future follow-up experiments will include these factors.

So what does this mean for the average person who doesn't want to be bitten by a mosquito?

Perhaps adjusting the color of your clothes has a chance to reduce your risk of being bitten, for example you can try to wear white, blue or green, and try to avoid black, red and orange, especially red and black plaid patterns.

But the effectiveness of these practices is not guaranteed, in particular, there are significant differences in color preferences between different mosquito species. But these findings do suggest that, with more in-depth research, color does have a chance to be used as a tool to control mosquitoes.

#创作团队:

Compile: M ka

Typography: Wenwen

#参考来源:

https://theconversation.com/mosquitoes-might-be-attracted-to-certain-colours-new-research-176423

https://www.sciencenewsforstudents.org/article/why-mosquitoes-bite-you-red-color-long-wavelengths-attraction

#图片来源:

Cover image: @Doug88888 via Flickr

首图：Simon Kutcher, AFAP. Contact via Flickr