A new study led by the University of Washington (UW) has found that, after using olfactory cues to detect potential hosts to bite, mosquitoes tend to fly towards specific colors, including red, orange, black, and cyan, while ignoring other colors such as green, purple, blue, or white. These findings help explain how mosquitoes find hosts, since human skin, regardless of its particular pigmentation, always emits a strong, red-orange “signal” to their eyes.
“Mosquitoes appear to use odors to help them distinguish what is nearby, like a host to bite,” said study senior author Jeffrey Riffell, a professor of Biology at the UW. “When they smell specific compounds, like CO2 from our breath, that scent stimulates the eyes to scan for specific colors and other visual patterns, which are associated with a potential host, and head to them.”
Professor Riffell and his colleagues tracked the behavior of female yellow fever mosquitoes (Aedes aegypti) when presented with various olfactory and visual cues. As in the case of all mosquito species, only A. aegypti females drink blood, and can transmit various diseases such as dengue and yellow fever, or those caused by the Chikungunya or Zika viruses. Finding what attracts and repels these mosquitoes is thus highly important for protecting ourselves from these diseases.
The researchers discovered that smelling carbon dioxide (CO2) – the gas that we and other animals exhale with each breath – boosts female mosquitoes’ activity levels, making them scan the environment in search for hosts. Without prior exposure to CO2, mosquitoes largely ignored a colored dot the scientists presented to them in the test chamber. After being exposed to this gas, mosquitoes continued to ignore the dot if it was green, blue, or purple, but immediately flew towards it if it was red, orange, black, or cyan.
These findings suggest that mosquitoes’ olfaction and vision are strongly related and that their eyes prefer certain wavelengths in the visual spectrum. Understanding these insects’ visual preferences can help us avoiding their disease-transmitting bites.
“One of the most common questions I’m asked is ‘What can I do to stop mosquitoes from biting me?’” said Professor Riffell. “I used to say there are three major 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, which can not only be found on your clothes, but is also found in everyone’s skin. The shade of your skin doesn’t matter, we are all giving off a strong red signature. Filtering out those attractive colors in our skin, or wearing clothes that avoid those colors, could be another way to prevent a mosquito biting.”
Further research is needed to determine how other visual and olfactory cues – such as skin secretions – help mosquitoes target potential hosts, and to clarify what are the colors and smells preferred by other species of mosquitoes.
The study is published in the journal Nature Communications.