‘London Underground’ mosquito has surprisingly ancient origins

Once thought to have evolved inside the Tube network, a tunnel-dwelling mosquito might actually have emerged thousands of years ago in Egypt

The *Culex pipiens* *molestus* mosquito thrives in the subterranean world of the London Underground. Credit: Martin Dohrn/Science Photo Library

A variety of mosquito once thought to have evolved in the tunnels of the London Underground seems to have originated alongside humans thousands of years ago in the Middle East, a genetic analysis reveals¹.

Culex pipiens molestus were notorious during the Second World War for biting Londoners sheltering from German air raids in the Underground’s tunnels and stations. The mosquito looks like the common house mosquito, Culex pipiens, but behaves very differently. For example, C. pipiens lives and breeds above ground, mates in swarms, bites birds and requires a blood meal before laying eggs. The molestus form breeds underground, can mate in confined spaces, bites mammals and can lay eggs without having dined on blood.

In the 1990s, scientists suggested that C. pipiens molestus could have evolved in the London Underground tunnels themselves², but populations of the same form have since been found underground in North and South America, Europe, Asia, Africa and Australasia, making this hypothesis unlikely.

To trace where the insects might have originated, evolutionary biologist Yuki Haba, now at Columbia University in New York City, evolutionary genomicist Lindy McBride at Princeton University, New Jersey, and their colleagues extracted DNA from 357 C. pipiens molestus mosquitoes collected from across Europe, North Africa and western Asia, including 22 historical specimens from the National History Museum in London. They then analysed variations between the mosquitoes’ genomes to identify the evolutionary relationships between populations.

Gradual evolution

The team’s results, posted on the bioRxiv preprint server, suggest that molestus mosquitoes first adapted to human environments above ground in what is now Egypt, over the course of more than 1,000 years, potentially in conjunction with the rise of agricultural civilizations. The fastest rate of genetic divergence between pipiens and molestus seems to have been about 2,000 years ago, says McBride.