Who would have thought that mosquitoes, the scourge of many an otherwise lovely summer evening, would leave us alone if we only smelled worse?  New research says the trick to the success of DEET, a chemical often used as the basis for many insect repellents, is its aroma.  To mosquitoes, DEET smells so bad they just don’t want to come near the stuff.

It was thought that DEET (N,N-diethyl-3-methylbenzamide) blocked a mosquito’s sense of smell, making it look elsewhere at feeding time.  Walter Leal, chemical ecologist and professor of entomology at the University of California, Davis, has discovered that, to a mosquito, DEET just stinks too much to be appetizing.

In 1946, the US Army was granted a patent on DEET although the exact mechanism of the repellent was not clearly understood.  DEET, now considered the industry standard for insect repellents, is used by more than 200 million people around the globe.

Previous theories have suggested DEET masks the aroma of the person, or host, wearing it or that it jams the mosquito’s ability to smell the host.  Leal and colleagues discovered a particular neuron on the mosquito’s antennae that detects the aroma of DEET, a discovery that may prove to be instrumental in the development and application of future insect repellents containing DEET and other chemical elements.

In Leal’s laboratory experiments, Southern house mosquitoes (Culex quinquefasciatus) were especially repelled by DEET-based solutions.  The Southern house mosquito is known to transmit lymphatic filariasis, a disease characterized by the infestation of tiny, threadlike parasitic worms, as well as West Nile virus and St. Louis encephalitis.

Leal’s groundbreaking study will be published in the August 18 issue of the Proceedings of the National Academy of Sciences.