Not only the smell of carbon dioxide, but also certain colors, especially red, attract the tropical disease mosquitoes Aedes aegypti, reports Nature Communications. However, these insects ignore other colors such as green, purple, blue and white.
Which colors attract mosquitoes?
Aedes aegypti is a carrier of yellow fever and dengue which are found in humans and monkeys in the subtropics and tropics, as well as chikungunya and zika diseases. These diseases cause many deaths, problems in the health care system and huge financial losses.
New research by scientists from the University of Washington (UW) in collaboration with the University of California, Santa Barbara and the German University of Freiburg, indicates that these mosquitoes – when they detect carbon dioxide we exhale – fly towards certain colors, including red. orange, black and cyan. They ignore other colors such as green, purple, blue, and white. Scientists believe these findings help explain how mosquitoes find a host: because human skin, regardless of overall pigmentation, sends a strong red-orange ‘signal’ to their eyes.
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Mosquitoes appear to use scents to help them recognize what is nearby as the host to bite, says Jeffrey Riffell, professor of biology at the University of Warsaw. – When they sense specific compounds such as CO2 from our breath, this smell stimulates the eyes to look for and target specific colors and other visual patterns that are related to the potential host.
Knowing which colors attract hungry mosquitoes and which ones don’t can help you design better repellants, traps, and other methods of fighting mosquitoes.
– One of the most frequently asked questions is: ‘What can I do to stop the mosquitoes from biting me? – points out prof. Riffell. – I once said that there are three main clues that mosquitoes attract: breath, sweat, and skin temperature. In this study, we found a fourth clue: the color red, which can be found not only on clothes but also in the skin of every person. The skin tone does not matter; we all emit red. Filtering out these attractive colors on our skin or wearing clothes that avoid these colors could be another way to prevent mosquito bites, she adds.
Color more important than fragrance
The researchers tracked the behavior of Aedes aegypti females when they were given different types of visual and olfactory cues. In all mosquito species, only female mosquitoes drink blood, and A. aegypti bites can transmit dengue, yellow fever, chikungunya and Zika diseases. Researchers tracked individual mosquitoes in miniature test chambers into which they sprayed certain scents and presented different types of visual patterns – such as a colored dot or a human hand.
Without any odor stimulus, the mosquitoes largely ignored the dot on the bottom of the chamber, regardless of color. After injecting CO2 into the chamber, mosquitoes still ignored the dot if it was green, blue, or purple. But if it was red, orange, black, or blue, the females would fly towards it.
Humans cannot sense CO2, the gas exhaled by us, and other animals with every breath, but mosquitoes can. Previous research by Riffell’s team and other groups has shown that sniffing out CO2 increases the level of activity of female mosquitoes – they search the space around them, possibly for a host. Experiments with colored dots have shown that, when scenting CO2, the eyes of these mosquitoes prefer certain wavelengths in the visual spectrum.
“Imagine you’re on the sidewalk and you smell cake and cinnamon,” said Riffell. – This is probably a sign that there is a bakery nearby and you can start looking for it. Here we started to learn what visual elements mosquitoes look for after sniffing their own version of ‘bakery’.
People see different wavelengths of light as distinct colors: for example, 650 nanometers look red, while 450 nanometers look blue. Scientists don’t know if mosquitoes perceive colors the same way. However, most of the colors that mosquitoes prefer to smell CO2 – orange, red and black – correspond to longer wavelengths of light. Human skin, regardless of pigmentation, also emits a long wavelength signal in the red-orange range.
When Riffell’s team repeated the experiments in the chamber with human pigment cards equivalent to the skin color – or with the researcher’s bare hand – mosquitoes again flew towards the visual stimulus after spraying CO2 into the chamber. If the scientists used filters to remove long wavelength signals or wore green gloves, the mosquitoes that smelled the CO2 no longer flew towards the stimulus.
The female preference for red-orange colors is determined by genes. Mosquitoes with a mutated copy of the gene needed to sense CO2 no longer showed color preferences in the test chamber. Another strain of mutant mosquitoes that could no longer “see” long wavelengths of light was “color blind” in the presence of CO2.
More research is needed to determine how other visual and olfactory stimuli – such as skin secretions – help mosquitoes target potential hosts at close range. Other mosquito species may also have different color preferences depending on the preferred host species.
Author: Paweł Wernicki.
- To avoid being bitten by insects, including by flies, mosquitoes and ticks, it is worth using Thief Oil – a fragrance against mosquitoes.