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Chemical to Trap Malaria Mosquitoes Identified

In a world first, researchers have found that a naturally occurring chemical attracts pregnant malaria transmitting mosquitoes - a discovery which could boost malaria control efforts. The chemical, cedrol, found in mosquito breeding sites near Africa's Lake Victoria, could be used in traps that would 'attract and kill' the female mosquito, preventing reproduction before she lays hundreds of eggs.

This is the first chemical confirmed to attract female mosquitoes after they have fed, while they search for a place to lay their eggs, and offers a new way to control mosquitoes. The researchers followed the Anopheles gambiae mosquito's journey: after a blood meal from a human, the female mosquito heads off to lays her eggs in a pool of still water.

The team noticed that some pools would be full of larvae, while others remained empty. The team set up a number of pools of water with different infusions, such as grasses, different soils, even rabbit food pellets, and judged which pools the mosquitoes preferred to lay in by counting the number of mosquito larvae in each. They quickly honed in on one particular soil, which they dubbed their 'magical mud'.

"We found the mosquitoes were more than twice as likely to lay eggs in water infused with this particular soil than in water fresh from Lake Victoria," said Mike Okal, a PhD student at the London School of Hygiene & Tropical Medicine, and corresponding author on the study. After various studies to confirm that it was an odour released from the soil infusion, rather than the look of the turbid water, that was attracting mosquitoes, the challenge was to isolate the precise chemical that drew them in.

Researchers identified a number of chemicals released from the soil-infused water and compared these with over 100 samples taken from natural mosquito breeding sites around Lake Victoria. They quickly honed in on one - the sesquiterpene alcohol cedrol - which was present in their soil infusion and was also found in more than 50 per cent of their natural habitat samples. The team confirmed that the mosquitoes were two times more likely to lay eggs in water with cedrol in the laboratory and a controlled field environment. During their field test, the team showed that wild mosquitoes were three times more likely to be caught in traps baited with cedrol than in traps with lake water alone.

"Our study for the first time has carefully demonstrated that egg-bearing Anopheles gambiae mosquitoes can detect the chemical cedrol and are drawn to it in real-world circumstances," said project leader Dr Ulrike Fillinger, from the London School of Hygiene and Tropical Medicine. PTI

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