Nation & World

INSECTS: Newly discovered chemicals jam mosquitoes' GPS

Move over, DEET.

UC Riverside scientists have discovered chemicals that blockmosquitoes from detecting carbon dioxide, which they use to findtheir unwilling blood donors.

The chemicals, found in ripening fruit, could be used as ingredients in new, safer mosquito repellents, said Anandasankar Ray, an assistant professor of entomology who discovered the chemicals with graduate student Stephanie Turner.

Ray said such repellents would be invaluable for reducing thespread of deadly tropical diseases, such as malaria and West Nile virus. Without their chemical global positioning system, fewermosquitoes will get closer to humans in the first place, Raysaid.

The most effective repellent now available, DEET, was recently found to be neurotoxic to mammals, raising the possibility it might be harmful to humans.

The research was published recently in the scientific journal Nature.

The existence of such chemicals has been suspected at least since 2006, when a study by scientists at Rockefeller University in New York found "receptors" in mosquito neurons that detect carbon dioxide. Receptors are molecules on the surface of cells that trigger events inside cells.

"A lot of labs around the world have been interested in trying to find volatile chemicals that fit these receptors," Ray said. "Fortunately, we were first."

Moreover, the chemicals block carbon dioxide detection for several minutes after exposure, Ray said.

Ray and Turner found the chemicals in a roundabout manner; they studied fruit flies as well as mosquitoes. Both use the same neural mechanism to detect carbon dioxide. The Rockefeller study also was performed on both mosquitoes and fruit flies.

The UC Riverside study found that hexanol and butanal ---- related to chemicals that work on fruit flies ---- block carbon dioxide detection in Culex mosquitoes, which transmit West Nile virus and filariasis.

However, mosquitoes and fruit flies use their carbon dioxide detection for very different purposes.

Mosquitoes use exhaled carbon dioxide to find their human meal tickets, so they are attracted by it. Fruit flies emit carbon dioxide as a response to stress, which is often associated with danger, so they flee from it.

The problem is that carbon dioxide is also emitted by ripening fruit, the flies' main food source. Because of that, some other chemicals emitted by fruit must be blocking the flies from responding to carbon dioxide, scientists reasoned.

And the race to find these chemicals was on; UCR's team won.

(How and why ripening fruit emits these chemicals is a fascinating topic. However, it wasn't addressed in the study, which was focused on identifying the chemicals).

Carbon dioxide isn't the only means mosquitoes use to find humans, Ray said, but it's the one that acts at the longest distance. Moreover, it also heightens their sensitivity to other cues, such as body heat.

As such, blocking carbon dioxide detection disrupts their navigational systems on multiple levels.


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