"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 Wednesday 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 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 proved to be a mini-ocean, comprising nearly half a million potential compounds. This was whittled down to nearly 200. Of these, 10 compounds seemed the most promising and were put to the test on fruit flies. Of the 10, eight turned out to be good repellents on fruit flies. Four of them were then tested on mosquitoes, all of which worked.