Why Some Mosquitoes Prefer Humans

Mosquitoes have been called the deadliest animal in the world: tiny creatures so dangerous that genetic engineering may be necessary to win the battle against them. But not all mosquitoes are equally responsible for devastating the human population by spreading disease. Out of thousands of species, only a few like to bite humans — and even within the same species, mosquitoes from different places can have different preferences. Why do some find us irresistible, while others remain unimpressed?

To answer that question, a team of Princeton researchers, working with a large network of local collaborators, spent three years driving around sub-Saharan Africa collecting the eggs of Aedes aegypti mosquitoes, which are responsible for Zika, yellow fever and dengue.

There are two subspecies of Aedes aegypti: one that prefers humans and one that prefers animals; most populations are a genetic mix. After sending the eggs to New Jersey to grow new colonies, and then tempting the insects with the sweet smells of human and of rodent, the researchers found that the more human-loving mosquitoes tended to come from areas with a dry climate and dense human population. That, in turn, is because humans provide the water mosquitoes need to breed.

“There had been quite a bit of speculation in the literature that the original reason this species evolved to be a human specialist had to do with its use of human water,” said Lindy McBride, a Princeton neuroscientist and an author on the study. “It’s easy to come up with hypotheses, but what was incredibly surprising was that you could actually see evidence for that.”