How mosquitoes acquired taste for human blood

A new study has revealed that body scent first attracted mosquitoes to acquire the taste for human blood.

The female mosquitoes that spread dengue and yellow fever didn't always rely on human blood to nourish their eggs. Their ancestors fed on furrier animals in the forest. But then, thousands of years ago, some of these bloodsuckers made the smart switch.

The researchers looked at two distinct populations of mosquito living just hundreds of metres apart in Rabai, Kenya.

One group of black mosquitoes, a subspecies called Aedes aegypti formosus, tended to lay their eggs outdoors and fed on forest animals.

Their light brown cousins, Aedes aegypti aegypti, which spreads yellow and dengue fever, chose to breed in water jugs and mostly hunted humans.

Analysis of the insects' genes revealed 14 strongly linked to liking humans that showed greater activity in the brown mosquito's antennae. However one, the odour receptor gene Or4, stood out.

The switch from preferring animals to humans involves a variety of behavior adjustments: Mosquitoes had to become comfortable living around humans, entering their homes, breeding in clean water found in water jugs instead of the muddy water found in tree holes.

Leslie B. Vosshall, the Robin Chemers Neustein Professor, said that it was a really good evolutionary move, as humans provide the ideal lifestyle for mosquitoes like they always have water around for them to breed in, they are hairless, and they live in large groups.

The study is published in the Nature.