PARIS – Researchers have discovered four natural mosquito repellents to succeed DEET, a compound dating to World War II.
DEET (the abbreviation for N,N-diethyl-meta-toluamide) was introduced by the U.S. Army in 1946 after troops deployed in the Pacific theater fell sick from malaria and other mosquito-borne diseases. It remains the primary insect repellent in use today, but has many limitations. It has to be applied frequently and is expensive, which rules it out for combating disease in regions where malaria is endemic. It also dissolves some types of plastic, synthetic fabrics and painted surfaces.
More worryingly, there is some evidence that flies and mosquitoes are developing resistance to it, and that the chemical disrupts an important enzyme in the mammalian nervous system called acetylcholinesterase.
In experiments that combined entomology and data-crunching, scientists at the University of California at Riverside uncovered four alternatives that may send DEET into retirement.
“The candidates contain chemicals that do not dissolve plastic, are affordable and smell mildly like grapes, with three considered safe in human foods,” said their study, published in the journal Nature on Wednesday.
The scientists’ first step was to understand how mosquitoes sense DEET and become repelled by it. For this, they turned to a cousin of the mosquito called the fruit fly.
The answer, they found, lies in a receptor called Ir40a, found in nerve system cells in a pitlike structure in the fly’s antennae.
The next step was to look for an odor molecule that would fit and activate the receptor, rather like a key turns a lock. It also had to be a natural substance, found in fruits, plants or animals.
The data pool comprised half a million potential compounds. This was whittled down to nearly 200. Of these, 10 were put to the test on fruit flies. Eight turned out to be good repellents on fruit flies. Four were tested on mosquitoes, and all worked.
Out of the four, three have already been approved as food flavors or fragrances by the U.S. Food and Drug Administration.
Called methyl N,N-dimethyl anthranilate, ethyl anthranilate and butyl anthranilate, they can be applied to bed nets, clothes and curtains to ward off insects, said the scientists.
The secret behind the breakthrough was to locate the Ir40a receptor and to screen potential chemicals, said Anandasankar Ray, an associate professor of entomology.
Ir40a, according to the probe, is highly conserved, a scientific term meaning that it shows little signs of evolutionary change and would be difficult for insects to adapt to. The receptor is also common across many flies and other insects that are a pest for humans and plants.
“Our findings could lead to a new generation of cheap, affordable repellents that could protect humans, animals and, in the future, our crops,” said Ray.