Urbanization May Be Enhancing Mosquitoes’ Taste For Human Blood

PRINCETON, N.J. – Some mosquitoes like to bite humans. Others like to bite animals. So what drives these pests to pick one or the other? According to a new study by Princeton University, urbanization may play a role in mosquitoes choosing to bite humans over animals.

Over 3,000 mosquito species exist around the world, but only a few of them prefer to bite people. These human-targeting species are not only an annoyance due to their itchy bites, but can also spread dangerous diseases. Understanding how and why mosquitoes have a taste for human blood throughout evolution can help us to control the spread of mosquito-borne illnesses. It can also help experts predict where outbreaks may occur.

Mosquito taste test

To determine what factors influence this preference, researchers are studying a specific African mosquito species known as Aedes aegypti. Mosquito eggs from 27 locations across sub-Saharan Africa were brought back to their lab. The New Jersey team then tested whether the mosquitoes prefer the scent of humans or the scent of animals, such as guinea pigs and quail. The study identifies two factors that drives mosquitoes toward human blood: dry climates and urbanization.

This image shows the kinds of human water storage containers where Aedes aegypti larvae thrive in areas with intense dry seasons and little natural habitat. (Photo credit: Noah H. Rose)

“Mosquitoes living near dense human populations in cities such as Kumasi, Ghana, or Ouagadougou, Burkina Faso, showed increased willingness to bite human hosts,” study author Noah Rose says in a media release. “But they only evolve a strong preference for human hosts in places with intense dry seasons–in particular, in the Sahel region, where rainfall is concentrated in just a couple months out of the year. We think this is because mosquitoes in these climates are especially dependent on humans and human water storage for their life cycle.”

It’s not the people, it’s the weather

While mosquitoes in dense urban areas do seem to show greater preference for humans, the researchers explain this is not likely the reason for evolving to prefer people. Urban areas are only present in modern society, making it unlikely this behavior was driven by evolutionary changes.

The study finds mosquitoes from areas with longer and hotter dry seasons also show a strong preference for humans. This points to insects adapting to new climates, with humans being the closest snack as a possible reason.

“I think it will be surprising to people that in many cities in Africa, this species actively discriminates against humans,” says lead researcher Carolyn McBride.

“It wasn’t living with people per se that made mosquitoes specialize in biting humans,” Rose adds in a university statement. “It was actually them adapting to these really hot and dry places where they lived intimately with humans.”

Unfortunately, based on their findings, the researchers say that the outlook for mosquito biting preferences is not promising. Both climate change and increased urbanization are likely to drive mosquitoes to bite more people throughout the next few decades.

In the future, the researchers plan to continue studying the link between mosquito preferences, climate, and urbanization. They also hope to study which specific genes and genetic changes influence the insect’s behavior.

The study is published in the journal Current Biology.

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