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[NAIROBI] A worn sock and a bottle of fermenting yeast could provide a cheap and effective trap for mosquitoes, according to a study.

Scientists testing ingredients for traps outside huts in western Kenya found that they could lure many mosquitoes away from their human targets using these simple components.

Mosquitoes follow carbon dioxide (CO2) gas because it is breathed out by animals, on whom they feed — in the case of humans, transmitting diseases such as malaria and dengue in the process.

Scientists already use traps baited with industrially produced CO2 to capture mosquitoes for study.

But scientists, from Wageningen University in the Netherlands, the University of Nairobi in Kenya and the Kenya-based International Centre for Insect Physiology and Ecology (icipe), wanted to see if they could produce a cheaper, household version.

The scientists baited some traps with the usual, industrially produced CO2. They baited others with CO2 produced by fermentation when yeast is mixed with a sugar solution.

Both options were tested in a variety of settings including 'semi-field' trials, and full field trials — where traps were hung under the eaves of four huts in Lwanda, a rural village in western Kenya, whose occupants were sleeping under bednets.

Nylon socks that had been worn by two of the scientists — to ensure they contained "human foot volatiles" — were added to some of the traps, with clean nylon socks added to others as controls.  

The top performing traps were those containing a combination of CO2 derived from the yeast mixture and worn socks.

In the semi-field trials, unbaited traps caught only five per cent of the mosquitoes that were released; worn socks alone trapped 43 per cent, and the combination of a worn sock and yeast-produced CO2 trapped nearly 80 per cent of released mosquitoes.

In Lwanda, where the trials were conducted among the naturally occurring mosquitoes, the results showed a similar pattern.

The scientists believe that the yeast may release other gases in addition to CO2, when it ferments, that are similar to other gases that humans produce.

Traps made using socks and yeast solution could, they say, "significantly reduce costs and allow sustainable mass-application of odour-baited devices for mosquito sampling in remote areas".

While producing CO2 from yeast using a bottle sugar and water is easy and possible in every African home, more research is needed to determine exactly what chemicals from the human scent attracted mosquitoes, said Wolfgang Schmied, one of the team, whose work was published in Malaria Journal (25 October).  

"The idea is not to stop closing windows or using bednets," Schmied said, "but the traps could become an additional building block in an encompassing mosquito control programme if they became cheap and effective enough".

Albert Otieno of icipe's human health division, who was not involved in the research, said that yeast-based traps could be made for less than US$6 dollars since yeast is easy to obtain and used bottles can be used as apparatus.

References

Malaria Journal, doi: 10.1186/1475-2875-9-292

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