Would It Be A Bad Thing to Wipe Out A Species ... If It's A Mosquito?

Enlarge this image Matthew Twombly for NPR Matthew Twombly for NPR

Mosquitoes have a nasty reputation.

The species Aedes aegypti, for example, is currently responsible for spreading the Zika virus through the Americas and also infects humans with dengue fever, chikungunya and yellow fever.

This raises the question: Should there be an effort to get rid of Aedes aegypti for good?

This story is part of NPR's ongoing coverage of Zika virus.

There have, of course, been many thousands of species that are indeed gone for good. And a U.N. Convention on Biological Diversity has noted: "Every day, up to 150 species are lost."

The list of extinct species includes dodos, Tasmanian tigers, passenger pigeons and the West African black rhinoceros. But it wasn't an intentional plan to eliminate them. In many cases, the extinction happened because of hunting and because humans took over the creature's habitat.

Conservationists have voiced their dismay at these losses. "The loss [of a species] is like the loss of a gallery of the masterpieces of the artists of old time," said Theodore Roosevelt.

On the other hand, if we were to wipe out Aedes aegypti, we'd cut down on the diseases they spread. But could there be unintended consequences? Would exterminating this species of mosquitoes backfire? Would their absence create some new ecological problem?

That's what researchers wanted to know when they studied the biting midge, a tiny bloodsucker that can spread diseases to animals and filarial worms to humans.

What we learned, says Dina Fonseca, a professor of entomology at Rutgers University, is that the biting midge is the only known pollinator of cacao.

"If we were to eradicate that particular disease vector, we may not have chocolate by the end of it," says Fonseca. "Which a lot of people would consider a catastrophe."

Humans haven't completely eradicated a mosquito species yet and studied the consequences. So we asked mosquito experts to speculate: Should we paint a target on the back of Aedes aegypti?

"It's sad the passenger pigeons were lost," says Andrew Read, a biologist and entomologist who specializes in the ecology and evolutionary genetics of infectious disease at Pennsylvania State University. "But did ecosystems collapse? No. Did anything bad happen? We just lost a pigeon, that's a shame."

"If we took out Aedes aegypti, that would be something," he adds. "Nothing good comes from them, just that people get really sick."

Fonseca feels similarly. "I'm not worried about eradicating an invasive mosquito. It's an urban species that specializes on feeding on people," she says. "The result of removing them is health to humans and more people."

Who are these mosquitoes that bedevil the human race? Aedes aegypti live in tropical and sub-tropical regions. They probably hitchhiked to the Americas in the 1600s on ships coming over from Africa. And they thrive in urban environments, especially in poor areas where people don't have running water.

These mosquitoes like to lay their eggs in containers where people store water. Half of the mosquitoes that hatch stay around the house. The other half don't stray far enough to places where bats or birds might have a chance to eat them.

It would be impossible to predict with complete certainty how ending this disease-carrying species of mosquito could affect the ecosystem. For one, there hasn't been much research around this topic. But the evidence scientists do have shows the impact would be small. Aedes aegypti are not a big food source for animals, and they don't pollinate plants.

"There's been lots of debate in the last 10 years whether we should eradicate mosquitoes, or at least the 100 species or so that serve as disease vectors for humans," says David Magnus, director of Stanford University's Center for Biomedical Ethics. "If you look at the science, the majority [of scientists] think we could probably eliminate mosquitoes without too much harm on the environment."

Fonseca says that she knows of some animals that increase their body mass by feeding on mosquito larvae — like migratory birds and fish in the Arctic. But she doesn't know of any species completely dependent on a particular mosquito.

That's not to say that everyone's on board with wiping out even one type of mosquito. "When push comes to shove I don't think most people are just going to be comfortable with the idea of eliminating a species just because we might be able to," says Bruce A. Hay, a professor at the Division of Biology and Biological Engineering at Caltech.

"We have to make every effort to be humble in recognizing the limits of our knowledge," warns bioethicist Magnus. "We ought to be very careful before we do anything that has irreparable consequences."

Nonetheless, he's on the side of elimination when it comes to Aedes aegypti: "I think you could make a pretty good case. As long as we're aware of the consequences of the change, it could be consistent with our obligations to being good stewards of the environment."

Jorge Rey, professor at the Florida Medical Entomology Laboratory, agrees.

"We don't know what the impacts are of eliminating these mosquitoes, but I wouldn't make an argument for keeping them, either," he says. "Eliminating the disease is priority one. Despite the consequences, it still has to be priority one."