Within minutes, mosquitoes, attracted to human or non-human scent, would grab a tube and enter. Later, the tubes were removed to count the mosquitoes and determine how many preferred Dr. Rose.
The resulting data revealed that mosquitoes that originally came from very dense areas, more than 5,000 people per square mile, liked humans more. (They also had more ancestry than the subspecies that humans prefer.) However, a more important factor was the weather. Specifically, mosquitoes that came from places that had a rainy season followed by a long, hot, and dry season much preferred humans.
Why? The scientists came up with an explanation that Brian Lazzaro, a professor of entomology at Cornell University who was not involved in the study, called “quite compelling.” Mosquitoes flourish during the rainy season, but then they must find a way to survive the dry season. Stagnant water, critical for mosquito breeding, is difficult to find in extremely arid environments. But it can be found around humans, who store water to live, so mosquito populations in arid regions evolved to take advantage of the situation.
Dr. Lazzaro also praised the team for sequencing the mosquitoes. That procedure revealed that human-loving mosquitoes were genetically distinct from animal lovers, and found that the preference for humans developed in one place and then spread throughout Africa. “They really see a single source for these mosquitoes that feed on humans,” he said. “That is a little surprising to me,” he added, because there could possibly be multiple instances of genetic adaptation.
The Current Biology article focused on evolutionary history, but its findings could have implications for public health. The results, combined with United Nations climate and population data, suggest that there will be more human biting mosquitoes in sub-Saharan Africa by 2050, caused primarily by urbanization.
“I think it is contradictory, because people know that the climate is changing rapidly, so that It should be the driving force, “said Dr. McBride. “But the climate characteristics that we consider important to this mosquito are not predicted to change strongly and clearly that would affect the mosquito.”
Urbanization, in contrast, is happening very quickly. “You could easily imagine that it has an effect on disease transmission in big cities,” said Dr. McBride.
