Undeniably, finding yourself covered in mosquito bites quickly spoils a pleasant summer evening. But more than just a nuisance, mosquitoes are also the deadliest creatures on Earth, due to the diseases they spread.
Much research is aimed at understanding their behaviors and prey preferences. We know that vision is an important sense in biting insects, a rule to which mosquitoes do not escape. Although they don’t rely solely on what they see, smell and temperature combine with visual cues to help them locate a host.
Previous research has sought to link particular colors (or the wavelengths of light that we perceive as distinct colors) to the host-seeking behavior of mosquitoes. The results, however, were inconclusive, with the same species showing preferences for different colors.
A recent study, published in February 2022 in the scientific journal NatureCommunications, is the latest to explore mosquitoes’ attraction to different colors. Could this research help us avoid being bitten by simply adapting the colors we wear? Let’s see.
The researchers conducted a series of experiments on three species of disease-carrying mosquitoes: mainly Aedes aegyptibut also Anopheles stephensi and Culex quinquefasciatus. In one of their experiments, they used a wind tunnel equipped with cameras to track the flight paths of mosquitoes. A tunnel has been designed to encourage them to behave as naturally as possible.
On the floor of the tunnel were two small colored dots, one representing the color (wavelength) sought and the other the control (white). Some of the color swatches were chosen to mimic different skin tones, including one representing the color of suntan lotion.
In mosquitoes, only females bite, as most species require a blood meal to complete the reproductive process. So 50 female mosquitoes, mated but not fed, were released into the wind tunnel, where they would naturally seek out a host.
After an hour, carbon dioxide (CO) was released into the wind tunnel. CO, exhaled by humans and other mammals, is odorless to us: but mosquitoes can smell it and use this odor to guide them to a source of blood.
Prior to the release of the olfactory stimulus, mosquitoes Ah. aegypti largely ignored the colored circles on the floor, instead exploring the ceiling and tunnel walls. But once CO was introduced, they began to study colored circles, especially as the wavelength increased from 510 nanometers (nm) to 660 nm.
These longer wavelengths represent colors in the orange and red ends of the spectrum, although mosquitoes Ah. aegypti were more attracted to red, then black. It should be noted that these wavelengths from orange to red are the same as those emitted by human skin tones. Blue, green and purple did not attract mosquitoes any more than the control.
When skin color dots were used, they attracted mosquitoes more than the control, but no preference was observed for a particular skin color.
Previous experiments have shown that mosquitoes are more attracted to contrasting colors, such as a checkerboard pattern, than to a solid color. The researchers also showed the mosquitoes different spots on identical and contrasting backgrounds. The Ah. aegypti were more interested in spots with high contrast to the background. Scientists believe this helps mosquitoes distinguish an object (person) from the background, even in low light. Contrast thus played a more important role in attracting mosquitoes than color itself.
As for Ah. aegypti, An. stephensi was attracted to black and red, with little interest in lower wavelengths. Cx. quinquefasciatus showed interest in violet/blue and red (interestingly, the opposite ends of the tested spectrum).
The researchers also conducted a separate experiment in insect cages to explore mosquitoes’ attraction to real skin tones. Six volunteers from different ethnic backgrounds were recruited to participate in this test. The control was a white glove placed in one window and the volunteers’ hands were held one by one in the other window to see if mosquitoes were attracted to a particular skin color.
It appeared that the latter were more attracted to the hands than to the white glove: but as with the points, there was no preference for a particular skin color.
What to conclude from this ?
This study highlights that mosquitoes are attracted to human skin colors, but only in the presence of CO, suggesting that the smell of human or mammalian breath may serve as an initial cue. . This confirms previous research that revealed that CO attracts mosquitoes.
The researchers further found that color and contrast were important factors for Ah. aegypti which revealed a preference for red, then black. The An.Stephensi have expressed an interest in colors similar to those of Ah. aegypti, although preferring black to red. Meanwhile, Cx. quinquefasciatus was attracted to different colors.
As the researchers acknowledged, their experiments did not take into account some other factors that influence host choice by mosquitoes. These include chemicals released by human skin, skin temperature, and sweat present on the skin. It would be instructive to include these factors in future experiments.
What does this mean for us who don’t want to be bitten? You can try wearing white, blue or green and avoid black, red and orange. Absolutely avoid red and black checkered patterns.
While adapting one’s clothing may reduce the risk of being bitten, there is no guarantee that it will or that it will be effective, especially given the apparent variation in color preferences between species. But these results suggest that with more research, color could become a mosquito control lever.