New insect repellent could mean bye-bye to DEET

Researchers said today they had discovered four natural mosquito repellents to succeed DEET, a compound whose origins go back to World War II.
DEET -- the abbreviation for N,N-diethyl-meta-toluamide -- was introduced by the US Army in 1946 after troops deployed in the Pacific theatre 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 combatting disease in regions where malaria is endemic.
It also dissolves 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 computing, scientists at the University of California at Riverside uncovered four alternatives that may send DEET into retirement after 67 years.

"The candidates contain chemicals that do not dissolve plastic, are affordable and smell mildly like grapes, with three considered safe in human foods," says their study published today in the journal Nature.
"Our findings pave the way to discover new generations of repellents that will help fight deadly insect-borne diseases worldwide."
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, or Drosophila melanogaster, one of the most closely-studied lab creatures of all.

The answer, they found, lies in a receptor called Ir40a, found in nerve-system cells in a pit-like structure in the fruit fly's antenna.
The next step was to look for an odour 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.