DEET has been the gold standard of insect repellents for more than six decades, and now researchers from the University of California, Davis, scientist have discovered the exact odorant receptor that repels them. They also have identified a plant defensive compound that might mimic DEET, a discovery that could pave the way for better and more affordable insect repellents. Findings from the study appear in the journal Proceedings of the National Academy of Sciences.
N,N-Diethyl-meta-toluamide, abbreviated to DEET, is a slightly yellow oil. It is the most common active ingredient in insect repellents. It is intended to be applied to the skin or to clothing, and provides protection against mosquitos, ticks, fleas, chiggers, and many other biting insects. More than 200 million people worldwide use DEET, developed by scientists at the U.S. Department of Agriculture and patented by the U.S. Army in 1946.
DEET serves as a true repellent in that mosquitoes intensely dislike the smell of the chemical repellent. A type of olfactory receptor neuron in special antennal sensilla of mosquitoes that is activated by DEET, as well as other known insect repellents such as eucalyptol, linalool, and thujone, was identified by the team in a 2008 study. There are currently two hypotheses regarding the olfactory receptor neuron mode of action; activation of ionotropic receptor IR40a vs. odorant receptor.
The researchers honed in on the 2008 study by examining the two families of olfactory receptors of the southern house mosquito, Culex quinquefasciatus, which transmits diseases such as West Nile virus.
One receptor group, ionotropic receptors, normally detects acids, bases and other water-soluble compounds. The researchers discovered, however, that a receptor from the odorant receptor group is directly activated by DEET.
They also detected a link between DEET and the compound methyl jasmonate, suggesting that DEET might work by mimicking a defensive chemical found in plants.
Mosquitoes are considered the most deadly animals on the planet, but unfortunately, not everyone who needs this repellent can afford to use it, and not all who can afford it can use it due to its undesirable properties such as an unpleasant odour. Vector-borne diseases are major health problems for travellers and people living in endemic regions. Among the most notorious vectors are mosquitoes that transmit the protozoan parasites causing malaria and viruses that cause infections, such as dengue, yellow fever, chikungunya and encephalitis.
For decades, the field concentrated on screening compounds for activity, with little or no understanding of how chemicals interacted with mosquitoes to discourage biting. Use of modern techniques that combine molecular biology, biochemistry and physiology has generated evidence on how mosquitoes perceive odours.