Apart from knowing that mosquitoes are attracted to the carbon dioxide that adults (also pregnant women and taller people) emit more than children, when it comes to biting us (remember that female mosquitoes are the ones that bite ), new research led by scientists at the University of Washington (USA), suggests that mosquitoes, after detecting this CO2, fly towards specific colors.
Color, whether of a flower or a warm-blooded host, is important for object recognition and location as far as mosquitoes are concerned. In the work, published in the journal Nature Communications , the researchers found that yellow fever mosquitoes (Aedes aegypti) fly toward specific colors , including red, orange, black, and cyan, but ignore other colors, such as green, purple, blue and white.
Bites from an A. aegypti mosquito can also transmit dengue, chikungunya, and the Zika virus.
The experiment
The scientists tracked mosquito responses to visual and olfactory cues in a test chamber. They tested how the insects responded to different colored dots on the bottom of the chamber, with or without a CO2 spray . They found that mosquitoes flew to a point if it was red, orange, black or cyan, and if they had first smelled CO2. Without carbon dioxide emission , the insects ignored these zones, no matter what color they were . However, they still ignored the green, blue, white or purple locations, even though they had been sprayed with CO2.
“Mosquitoes appear to use odors to help them distinguish what is nearby, such as a biting host,” explained Jeffrey Riffell, lead author of the study. “When they smell specific compounds, like the CO2 in our breath, that smell stimulates their eyes to look for and target specific colors and other visual patterns that are associated with a potential host.”
The results reveal how the mosquito’s sense of smell (humans can’t smell CO2, but mosquitoes can), influences how the mosquito responds to visual cues.
“These experiments present the first steps that mosquitoes use to find hosts,” says Riffell.
Previous studies, including work by this same team of researchers, have shown in the past that smelling CO2 increases the activity level of female mosquitoes; it encourages them to search feverishly around them, looking for a host.
The researchers believe these findings help explain how mosquitoes find hosts to bite, since human skin, regardless of overall pigmentation, emits a strong red-orange “signal” in the eyes of mosquitoes. So regardless of our skin tone, lighter or darker, we all give off a strong red color signature.
“I used to say that there are three main cues that attract mosquitoes: your breath, your sweat, and the temperature of your skin. In this study, we found a fourth cue: the color red,” the authors comment.
Although we do not know if these insects perceive colors in the same way as human eyes , it can be concluded, based on this finding, that most of the colors that mosquitoes prefer after smelling CO2 (orange, red and black ) correspond to longer wavelengths of light.
Also, knowing which colors attract hungry mosquitoes and which ones don’t can help us design better repellents, traps, and other methods to keep mosquitoes at bay, especially when it gets hot.
Referencia: D. Alonso San Alberto et al. 2022. The olfactory gating of visual preferences to human skin and visible spectra in mosquitoes. Nature Communications 13, 555; doi: 10.1038/s41467-022-28195-x
