Hard to believe, but It's actually very difficult to attract mosquitoes. "Every time a mosquito sneaks up to an animal, thousands times its size to feed, it is trying to pull off something extremely dangerous," said Matthew DeGennaro, a mosquito geneticist and professor at Florida International University. The right cues to attract mosquitos is a whiff of exhaled carbon dioxide, warmth, a bit of body odor, other mysterious elements of animal smell - have to be there, or mosquitoes won't take the risk.
To design traps that could lure mosquitoes, scientists would love to know how they are picking up on these cues. In a paper published Thursday in Current Biology, Dr. DeGennaro and colleagues report that they have unraveled part of the mystery: They've identified a receptor in the mosquito's antennae that allow the insects to detect lactic acid, a substance from human sweat that bugs find very attractive.
The work began years ago when Dr. DeGennaro, then working in the lab of Leslie Vosshall at Rockefeller University, identified another odor receptor mosquitoes used to home in on its prey. However, even with that receptor destroyed, mosquitoes could still find humans as long as carbon dioxide was floating around. That suggested that other receptors, presumably ones that detect carbon dioxide, were compensating for the loss.
Dr. DeGennaro and his colleagues went in search of these other players, starting with a receptor called Ir8a. Its role was not yet clear. The researchers put mosquitoes that had been engineered to lack Ir8a into chambers where they were exposed to various combinations of carbon dioxide, lactic acid, warm temperatures and the arms of human volunteers.
Keeping track of what the mosquitoes were attracted to under these different conditions revealed that the mutants had problems. "We just did a simple behavioral test to whether they could respond to lactic acid," said Dr. DeGennaro. "And they couldn't."
Lactic acid was identified decades ago as one of the important signals in human sweat for drawing mosquitoes. But until now, it was not clear how mosquitoes perceived it. The knowledge could eventually lead to repellents that hamper the normal functioning of Ir8a, or aid in the construction of effective traps, Dr. Gennaro said.
Diseases like Zika, West Nile, dengue and malaria are spread by mosquitoes, and keeping their numbers down is an important global public health goal. New, effective strategies for mosquito control that can be used in combination with each other are crucial, Dr. DeGennaro said. The use of an insecticide alone, for instance, encourages the development of insects that are resistant. But with traps, chemicals to kill larvae and other tools deployed at once, it's possible to have an impact.
However, the identity of the receptor or receptors that pick up on carbon dioxide still remains mysterious. Dr. DeGennaro and colleagues believe it may be in the same group of receptors as Ir8a, but they have not found it yet. The quest continues.
