The Secret's Out

We know it works, but how?

Just how does DEET work? Does it jam the senses of a mosquito? Does it mask the smell  of the host?

You spray the chemical repellent on your arm and thankfully, those darn skeeters leave you alone.  They need a blood meal to develop their eggs, so off they buzz to find another host, one that's not so inhospitable.

But why do mosquitoes avoid DEET?

Well, they avoid it because it smells bad to them. Yes, they can smell it--that's why they avoid it.

The groundbreaking research, the work of UC Davis chemical ecologist Walter Leal and researcher Zain Syed, is published today in the Proceedings of the National Academy of Sciences (PNAS), which lifted the news embargo at 2 p.m., Pacific Standard Time.

The research contradicts a Science article published in March by researchers at Rockefeller University, New York. The researchers, as other scientists have long believed, said mosquitoes can't smell DEET because it jams the odorant receptors in insect nervous systems.

The Leal-Syed research solidly establishes the real mode of action.

Noted entomologist James "Jim" Miller of Michigan State University praised the Leal-Syed work as correcting “long-standing erroneous dogma.”

Said Miller: "For decades we were told that DEET warded off mosquito bites because it blocked insect response to lactic acid from the host -- the key stimulus for blood-feeding. Dr. Leal and co-workers escaped the key stimulus over-simplification to show that mosquito responses -- like our own -- result from a balancing of various positive and negative factors, all impinging on a tiny brain more capable than most people think of sophisticated decision-making.”

“This new work corrects long-standing erroneous dogma, and shows that recent work on DEET mode-of-action published in the flagship journal, Science, apparently was flat-out wrong,” Miller said. “One of the great attributes of science is that, over time, it is self-correcting."

Leal, past president of the International Society of Chemical Ecology  and former chair of the UC Davis Department of Entomology, said previous findings of other scientists showed a “false positive” resulting from the experimental design. 

Now that we know that skeeters can smell it, this will no doubt lead to better methods of insect control. Or, as Major Dhillon, president of the American Mosquito Control Association and district manager of the Northwest Mosquito and Vector Control District, Riverside, said: ”In the future, this new knowledge can be incorporated into developing new repellents and may be in control strategies for Culex quinquefasciatus and other mosquitoes.”

Those darn female mosquitoes, always in a “Let-us-prey” mood, have clearly met their match: the "why" behind "Let us spray."