Chemicals which interfere with a mosquito's ability to sniff out humans have been developed by US researchers, according to research in Nature.It is hoped they could be used to develop the next generation of mosquito traps and repellents.A UK expert said the discovery could be a "major step forward" if the chemicals were safe and cheap.Female mosquitoes use carbon dioxide in people's exhaled breath to find their next meal.They can detect minute changes in the concentration of the gas and track it back to a human breath.This knowledge is already used in carbon dioxide traps, but requires dry ice or gas cylinders - which mean they are rarely used in developing countries.Researchers have been looking for chemicals which can disrupt or confuse a mosquito's carbon dioxide sense.