Mosquitoes Show Strong Preference for Red, Orange, Black and Cyan in CO2‑Stimulated Tests

Researchers from the University of Washington, the University of California, Santa Barbara, the University of Alberta and the University of Freiburg conducted a 3‑D tracking experiment with Aedes aegypti mosquitoes. Analyzing more than 1.3 million flight trajectories, they tested the insects' visual response to colored dots with and without carbon‑dioxide (CO₂) present.

When only filtered air was supplied, only 1‑4 % of mosquitoes showed interest in any color. Adding CO₂ increased the proportion to about 21 %, with strong attraction to orange, red, black and cyan objects. The insects ignored violet, blue and white even in the presence of CO₂. The scientists concluded that CO₂ triggers a visual search for long‑wavelength colors, which are associated with potential hosts. Mutating the gene for CO₂ detection eliminated the color preference. The findings were published in *Nature Communications*.

"CO₂ stimulates the eyes to search for specific colors," said Jeffrey Riffell, a biology professor at the University of Washington.