Why Eradicating Earth’s Mosquitoes To Fight Disease Is Probably a Bad Idea
Hint: no one knows for sure what the consequences would be.
The Zika virus has been spreading across dozens of major countries, blazing a trail of tragedies and fear. On Saturday, officials with the World Health Organization announced that they feared the outbreak could be a larger threat to global health than the Ebola epidemic.
Scientists and politicians are looking for solutions and, as often happens in the midst of the outbreak of any mosquito-born illness, some have brought up an age-old idea: kill every mosquito on Earth. In an article for Slate published Friday, columnist Daniel Engber argued that the total and complete eradication of mosquitoes is our best option for fighting infectious disease.
But what would a world free of mosquitoes look like? Would it be an Earth in which the infectious diseases that plague millions are completely, permanently, and mercifully wiped out? Probably not. In fact, the eradication of an entire species could bring along with it an endless string of unforeseen consequences, one that could possibly be worse for humans than the problems we have now.
"We don't need to wipe them all out to dramatically reduce the burden of mosquito-borne disease globally."
The need to deal with the enormous and heartbreaking problem of mosquito-borne illnesses is more urgent than ever. In 2014, Bill Gates famously introduced the mosquito as the "deadliest animal in the world," citing that mosquito-borne illnesses kill some 725,000 people each year. Malaria alone kills 6 million people every decade. Then there's Dengue Fever, West Nile virus, chikungunya, and a host of other deadly illnesses, all brought about by tiny, bloodsucking mosquitoes. In fact, mosquitoes, despite not carrying sharp teeth or large body size, are deadly only in their ability to carry and transmit disease.
It makes sense then that, when faced with human death on an unimaginable scale and among some of the poorest populations on Earth, people would want to destroy the agent causing it.
Engber's vote is for a "nuclear option," an insect genocide much more aggressive than the current strategy: a series of smaller, controlled actions called Integrated Mosquito Management. In places where mosquito-borne illnesses break out, the use of chemical sprays and filling in swamps are common courses of action. But in some parts of the world, a series of scientific innovations are already being tested out that can wipe out large populations of insects at once. Engber proposes ramping these particular efforts to combat mosquitoes and the illnesses they carry.
One of these projects involves genetically sterilizing male mosquitoes, and then releasing them into the general population, where they will only create male offspring when they reproduce. With only males left, the populations will slowly start to die off, some scientists say. Another approach causes the offspring of genetically modified mosquitoes to die before they reach adulthood.
Mosquito eradication technology to target harmful species is a hopeful option—but it can't be the only solution, according to Cameron Webb, an expert on mosquitoes and infectious diseases at the University of Sydney.
"We should be careful not to put all our eggs in one basket," he said. "High tech solutions may be in the spotlight but we shouldn't erode the framework of traditional programs." These include community education, improved healthcare, better diagnostics to identify disease, reducing mosquito habitats around the home, insect repellents, bednets, vaccines and judicious use of insecticides.
While it might seem like an attractive option, there are quite a few reasons why killing off the world's mosquitoes is a bad idea for both people and ecosystems. For one thing, says Webb, there are thousands of different mosquito species found across the planet, and relatively few of them impact human health.
"In fact, outbreaks of disease caused by Zika, dengue, chikungunya and Yellow Fever viruses are primarily spread by just a couple of species," Webb told Motherboard, adding that the most prevalent disease-causing mosquito is the Yellow Fever mosquito, Aedes aegypti.
"Perhaps the time has come for us to consider complete eradication of mosquitoes," said Webb, noting that eradicating just that species in places that are inhabited by humans seems like a more sensible goal. "But we don't need to wipe them all out to dramatically reduce the burden of mosquito-borne disease globally."
As Engber himself admits, "no one really knows for sure" what the ecological implications would be (in fact, Slate also published a video on this very topic last June). On the one hand, there are hundreds of ecologically and economically important species of birds, bats, and fish who feed on mosquitoes. On the other, a feature in Nature in 2010 found that there were no species who relied solely on mosquitoes—a fact which Engber uses to assume that, without mosquitoes, other species wouldn't suffer.
Eradicating one vector of a disease doesn't always amount to wiping out the disease itself
"We haven't found an animal yet that relies on mosquitoes as a staple item in its diet but they're abundant snack food," said Webb. "I have little doubt that these mosquitoes are playing an ecological role and their eradication could have knock-on effects."
And yet, while public health entomologist Grayson Brown told io9 in 2014 that mosquitoes could, foreseeably, be wiped out, "the ecological damage that would be necessary... would make eradication not worth it unless there was a very serious public health emergency." It's pretty much impossible to estimate the total number or biomass of mosquitoes, but one estimate suggests that in the state of Alaska alone, mosquito biomass is equal to 96 million pounds. With such a staggering number of individuals, it's undeniable that there would long term consequences to mosquitoes' eradication.
What's more, ecology isn't a two way street, wherein the loss of one species impacts the survival of its predators only. Rather, ecological systems are like a blindingly complex series of spaghetti junctions, and one organism alone can touch the lives of so many others in ways that are often unseen, unpredictable, and unknowable. In the case of public health issues, eradicating one vector of a disease doesn't always amount to wiping out the disease itself.
When David Quammen, a science writer who reported out a book on animal infections and the next big pandemic, was asked this very question on an episode of Radiolab in 2014, he responded by pointing out that the loss of mosquitoes could leave an ecological niche open for other harmful insects, like filaria flies, which also bring along with them deadly illnesses.
"When you talk about trying to foresee the consequences of completely eradicating any one species, we just don't know," he said.