While a commercially available repellent is a long way off, laboratory tests produced "astonishing" results with some chemicals repelling insects for as long as 73 days and many working for 40 to 50 days.

This compares with an average repellent time of 17.5 days with DEET (n,n-diethyl-m-toluamide), the study, in the latest edition of Proceedings of the National Academy of Sciences, says.

DEET repellents offer broad-based protection from a variety of insects, however mosquitoes continue to spread diseases such as malaria and dengue fever, the paper says.

"It would be good to have more effective repellents that protect against a greater number of insect species," says Dr Ulrich Bernier, a research chemist with the Mosquito and Fly Research Unit of the US Department of Agriculture (USDA) who worked on the project.

Back in the 1940s, it took USDA scientists a decade to screen 40,000 chemical compounds in a search for new and more effective insect repellents.

That quest ultimately led them to DEET.

Potential

This time around, the research team was able to screen thousands of potential compounds in a matter of months using a drug discovery computer program that uses information about chemical structures and insect receptors to predict repellents' effectiveness against mosquitoes.

They focused the search on compounds known as N-acylpiperidines (related to the active ingredient in pepper).

The program allowed the scientists to narrow a field of 2000 compounds down to just 34, which they then tested on human volunteers in the laboratory.

Volunteers in the research test the effectiveness of one of the new repellents (Gary Clark)

Volunteers wore arm patches impregnated with standard doses of each compound and were exposed to caged mosquitoes.

The researchers measured the compounds' persistence, the time until repellence wore off which is signalled by the onset of insect biting.

The research, partly funded by the US Department of Defence identified 23 compounds that were "equivalent to or better than DEET in duration of protection".

"Astonishingly, a number of these protected more than three times as long as DEET," the paper says.

The researchers plan to continue testing on seven of the most promising compounds in their quest to identify the next generation DEET and will be looking to see how effective they are against a range of insect species.

Source:  ABCNews