What if we eradicated mosquitoes?

April 15, 2016

Dear Cecil:

Malaria, dengue, yellow fever, West Nile, chikungunya, and now Zika. All transmitted by mosquitoes, resulting in tens of millions of deaths and an untold number of ruined backyard barbecues. What would be the effect on our ecosystem if we could somehow wipe these little pests from the face of the earth? Would we do more harm than good?

Cecil replies:

Good news, Bill: we wouldn’t even need to get of all the mosquitoes. In fact, of the 3,500 mosquito species that humans have so far identified on earth, only a couple hundred or so give us trouble. And technology-wise, we’re better equipped to go to war with mosquitoes now than ever before. In decades past, efforts at eradication might’ve involved, say, draining a lake or DDT-ing a forest, triggering some massive downstream effects on the ecosystem. These days male mosquitos can be sterilized; we can engineer an “extinction gene,” to spread quickly through a mosquito species’ gene pool and ensure its death; we can infect species with harmful bacteria. In short, these are heady times in the mosquito-killin’ racket.

So there’s not much somehow about it — sooner or later, we will be able to get rid of mosquitoes. But, as the existence of Pumpkin Spice Oreos teaches us, just because one can do something doesn’t mean one should. Let’s consider pros and cons.

As you point out, humanity’s exposure to deadly viruses would plummet. According to stats compiled by the Gates Foundation, mosquitoes kill about 725,000 people a year, 600,000 from malaria alone; if you’re keeping track, you’ll find this means mosquitoes kill more people every year than people do. And we’re great at killing people. Sickness and death aside, sub-Saharan Africa — not exactly a prosperous region to begin with — could, by some estimates, recover about 1.3 percent of the GDP its countries currently spend on malaria-related costs. Malaria’s just the star of the show here, of course; plenty of supporting characters, including the ingenue Zika, have the potential to wreak havoc on humanity. There would be some ecological side effects to mosquito extirpation, which we’ll get to in a moment, but most scientists think they wouldn’t be particularly severe — that ecosystems would quickly evolve to fill whatever beneficial niche the mosquitoes might currently hold.

Also in the good news column, there’s recent precedent for such a campaign: the eradication from North America, and most of Central America, of the New World screwworm fly, a particularly nasty little insect that infests its vertebrate hosts with its larvae — that is to say, its maggots — and causes physical as well as economic pain, particularly if it gets in your livestock. (Screwworms made a memorable appearance in the media about ten years ago when a 12-year-old girl from Connecticut, upon returning home from a trip to Colombia, was found to have 142 larvae living in her scalp.) Anyway, a 2005 paper estimated that, following a 45-year campaign to get rid of the insect — using the sterilization technique — the U.S. saves about $800 million annually, mostly from avoiding livestock damage; Mexico saves $292 million; etc. As importantly, there don’t appear to be any downside effects on ecosystems, either.

Of course, there’s a hell of a lot more mosquitoes out there than there were screwworms. Shifting our view north, for instance, we find that mosquitoes play an important ecological role in the Arctic tundra, where their elimination would probably have the biggest impact. Some estimates have migratory bird populations in the tundra dropping by about half; reindeer migration patterns might change too, with corollary effects on other species. Elsewhere, spiders, lizards, frogs, and other insects all rely on mosquitoes as a primary food source. The mosquitofish — named for the larvae that are a staple of its diet — could be in for some tough times.

Not everybody’s in agreement about these predictions, though, whereas scientists do generally agree that mosquito eradication would engender far more good than harm: as one entomologist pointed out in the journal Nature, “The ecological effect of eliminating harmful mosquitoes is that you have more people. That’s the consequence.” (Great, right? Well, here’s where I point out that the nature writer David Quammen has celebrated mosquitoes’ unique ability to beat back human encroachment. Through their knack for making people miserable, Quammen suggests, they've undoubtably helped save some tropical forests from clear-cutting — he calls them “ecological heroes.”)

Don’t get too excited about our mosquito-free future just yet, though, Bill. Some ecologists suspect the benefits of eliminating disease-carrying mosquitoes would be only temporary: the other species that come to occupy their places in the food chain may well take over their disease-vector duties in the process — conceivably we could wind up dealing with something worse instead. Among those signing onto this more bearish position, I’ll note, is the American Mosquito Control Association, founded 80 years ago to promote public health and quality of life through the dissemination of mosquito-whacking knowhow. The pessimistic take on eradication may be proven right, but what else would you expect these guys to say? When mosquitoes are finished, the AMCA is too.

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