Genetically Modified Mosquitoes Have Come to the U.S. Will They Work?

“Our Mosquito Project Takes Flight,” reads a baby-blue billboard off US-1 in the Florida Keys, alongside an image of an insect tracing a path in the shape of a heart. Sponsored by the local mosquito control board and U.K.-based biotech firm Oxitec, the ad promotes a contentious plan to release millions of genetically modified Aedes aegypti mosquitoes here to test a new method of bioengineered pest control. It’s the first-ever such experiment in the United States, and one that has turned this chain of sun-soaked island communities into a battleground over scientific truth, government authority, and humanity’s right to modify nature. Even this bit of roadside signage is contested. Four months ago, the billboard carried a different ad, paid for by the Coalition Against GMO Mosquitoes, an organization with the mission of stopping releases of the genetically modified insects in the U.S., “WARNING!!!,” it read then, “GENETICALLY MODIFIED MOSQUITOES TO BE RELEASED IN THE KEYS!!”

That release began in late April, when, after a decade of planning, regulatory review and debate, Oxitec workers and local mosquito control personnel added water to a dozen plastic boxes containing the company’s “Friendly™” mosquito eggs in six locations around the Keys, triggering their hatching process.

Oxitec’s Aedes aegypti mosquitoes—which the U.S. Environmental Protection Agency (EPA) approved for use last year—are genetically modified to include a “self-limiting” gene that produces a fatal protein. The mosquitoes are raised in a laboratory in the presence of tetracycline, an antibiotic that prevents the added gene from activating. The mosquitoes’ eggs are then left to hatch in the wild, without the antibiotic. The gene kills immature egg-laying females—the only ones that bite—but the males reach maturity, mate with wild females, and pass on their faulty gene. Then their female progeny die, causing the bloodsuckers’ population to crash.

About 1,000 mosquitoes will emerge from each of Oxitec’s boxes each week. All told, 140,000 will be released in the current phase of the trial, which will last at least through July, while nearly 20 million will take flight in the second phase beginning later this summer. Oxitech says that in a previous experiment in Brazil, mosquito populations fell by up to 95% during a 13-week trial. The goal of the Florida release is to gather more information and reproduce the company’s past results, in order to demonstrate to U.S. regulators that the technology works.

Oxitec CEO Grey Frandsen says his company’s work is nothing short of existential for humanity. Mosquito-borne diseases already kill more than 1 million people worldwide every year, and climate change stands to expand the range of the insects and the pathogens they carry to regions where they could not thrive before, lending even more urgency in the race to develop new countermeasures like Oxitec’s gene editing technology. The COVID-19 pandemic, meanwhile, has underscored our vulnerability to massive outbreaks of infectious disease—many of which spread via mosquitoes. “We are seeking to develop and scale new technologies that will in essence allow the human race to continue to exist on this planet,” says Frandsen. “Insect pests are one of the most significant threats to that.”

But anti-genetically modified organism (GMO) sentiment runs hot across the U.S.—around half of American adults distrust genetically modified foods, for instance—and some locals here in the Keys are less than thrilled to be at the center of a massive genetic experiment. “I think the company just thinks that we’re dumb,” says Mara Daly, a mother and business owner who’s been fighting Oxitec for years. Daly and others like her worry the modified mosquitoes could cause unforeseen health or ecological repercussions. Officials at the company say people like Daly represent a minority spreading fear and distorting scientific truth in an effort bankrolled by large anti-GMO organizations. “Oxitec is slandered,” says Frandsen. “We are called every name in the book.” Members of the Florida Keys Environmental Coalition, part of the local Coalition Against GMO Mosquitoes, say their concerns are reasonable, that they are an all-volunteer organization with “no money and no budget,” and point to a petition with over 200,000 signatures against the Oxitec project, as well as a letter signed by dozens of local doctors asking for additional testing, as a measure of their support. Oxitec declined to put TIME and other journalists in touch with local residents hosting its mosquito release boxes, citing privacy as well as concerns about potential disruption by the company’s opponents, which never materialized.

Equipped with two airplanes and six helicopters, the hangar at Florida Keys Mosquito Control District (FKMCD)’s Marathon, Fla. headquarters feels like a military operation. That’s appropriate, as its agents here are engaged in a kind of war, flying constant sorties against enemy forces that could spread illness across these subtropical islands if left unchecked. Every day, dozens of FKMCD inspectors fan out through the Keys to sample standing water for mosquito larvae. They destroy small breeding sites themselves; to deal with larger ones, like ditches or swamps, they call in an airstrike. Often within an hour, a chopper roars overhead, its pilot using guidance software to drop payloads of ground-up corn cobs coated with soil bacteria intended to kill water-bound mosquito larvae. When swarms of insects take to the air, FKMCD dispatches the big guns: a Britten-Norman Islander turboprop outfitted as an insecticide carpet-bomber.

The Aedes aegypti mosquito—first catalogued by Europeans in Egypt in the 1700s—might seem a bit delicate to merit such tactics. The long-legged arthropods dart around their targets as if in hesitation, ducking in for a small sip of blood when the opportunity arises. “Aedes aegypti dances,” says Rajeev Vaidyanathan, a medical entomologist and Oxitec’s director of U.S. programs, speaking at FKMCD headquarters. Just a few minutes earlier, Vaidyanathan identified an Aedes aegypti in the outfit’s hangar by its flight pattern, a holdover from ancestors that preyed on rodents. “If you were to try to dance with a rodent, you’ve got to be careful,” he says. “You have to bob and feint like a boxer.”

Even if they move like a featherweight—and account for only 4% of Keys mosquitoes—Aedes aegypti are a heavyweight health hazard. They feed almost exclusively on humans, and can transmit Zika and Dengue viruses. In that sense, their name is appropriate—”Aedes” is Greek for “unpleasant.” Their touch-and-go feeding style means a single insect often bites multiple people living in close proximity to one another. “That’s why you see Dengue cases the way you do—a child, a grandmother, a housekeeper,” says Vaidyanathan. “You get clusters of Dengue in a household.”

The FKMCD’s firepower is becoming less effective as Aedes aegypti and other insects grow increasingly resistant to chemical pesticides. In 2009, the Keys saw its first outbreak of the often life-threatening Dengue virus in decades, in which up to 1 in 20 residents of Key West’s Old Town were infected, prompting local officials to approach Oxitec for a solution. Zika virus, linked to devastating neurological disorders, made its way to Florida in 2016, causing further alarm. Multiple scientists told TIME that these incidents show it’s urgently necessary to develop technologies like Oxitec’s. “People in Florida, they’ve got a huge nuisance problem from mosquitoes,” says John Mumford, an ecologist at Imperial College London. “They’re very fortunate that they don’t have a huge disease problem.”

Oxitec’s work almost immediately became controversial among locals like Ed Russo, the president of the Florida Keys Environmental Coalition. Even among Keys dwellers, who are known for being quirky, Russo stands out. For one thing, the 75-year-old business owner was an environmental consultant for former U.S. President Donald Trump. (He’s doing “much better” since the election, Russo says. “This last Wednesday I had lunch with him. He was breaking balls like the old days.”) The night before Oxitec’s release announcement, Russo invited TIME to an outdoor dinner, where he ordered scotch and held forth, railing against the company. In part, he and his allies are concerned that Oxitec’s mosquitoes could have unintended effects on residents and their environment. “I’m an environmental guy, but I’m not crazy,” Russo says. “If we’re going to introduce an experimental pesticide, let’s do it in a responsible way and do it in a transparent way.”

Other local activists feel that Oxitec hasn’t always been entirely forthright. Daly, for instance, points to press releases, one issued just last month, in which the company and the FKMCD said that the U.S. Centers for Disease Control and Prevention “confirm[ed] their collaboration in the project,” and will “provide independent project evaluation.” But in April, the CDC told Daly that it was not evaluating or overseeing Oxitec’s work. CDC Public Affairs Officer Tom Skinner told TIME that the agency is supportive of Oxitec, that it helped develop the protocol for the Keys project, and that it plans to help Oxitech evaluate the resulting data. However, Skinner said the CDC will not be able to access the program the way it normally would, partly due to COVID-19 restrictions.

Asked if it is accurate to say the CDC is “collaborating” on the project, Skinner says it is not, “as far as actually providing people there on the ground,” nor is it funding the effort or the company. Asked to rectify the discrepancy, an Oxitec representative said the company and the CDC had previously “envisioned” the agency sending personnel.

The anti-Oxitec contingent also says the company has been a bully in local politics. They say they were outmatched by Oxitec’s money, which, for example, helped fund radio ads, direct mail and door-knockers in the lead-up to a non-binding 2016 referendum on the company’s mosquito releases. Public records show that Intrexon Corp., then Oxitec’s parent company, spent $176,000 funding a group called the Florida Keys Safety Alliance that was “dedicated to informed decision-making” on the release of GM mosquitoes in the lead-up to that vote. (An Oxitec spokesperson says that the company’s efforts were meant to counter “falsehoods and misinformation” spread by anti-GMO groups.) The broader referendum passed handily in the Keys, though a local proposition on the project failed in Key Haven, where officials had originally been planning to release Oxitec’s mosquitoes. (The release was later moved; FKMCD officials said they picked the new zones based on the referendum results, as well as local mosquito populations and EPA guidelines. )

Since then, locals who oppose the project, as well as some outside observers, say Keys residents have gotten little input into the process, and some are only now learning about the release as it is already underway. “This is a very bad thing from a democratic perspective,” says Sandra Schwindenhammer, a political scientist at the University of Giessen in Germany who has researched Oxitec and GMO governance. “You can try to explain why decisions were made and why they do it the way they do it, but local people don’t have the possibility really to make a change in the process.” Oxitec representatives say that over the course of 10 years since local officials invited the company to work in the Keys, it has carried out “what may be one of the most proactive public engagement efforts anywhere in the world in relation to a vector control technology.”

The company’s opponents have also had their chances to maneuver politically, and haven’t always taken them. Last year, for example, three of five seats on the local mosquito control commission collaborating with Oxitec were up for election, but none were contested.

Whether or not the allegations of unfair politicking hold up, on the question of the science of Oxitec’s work, at least some of the activists’ concerns lack sound footing. One anti-Oxitec billboard, for example, suggests getting bitten by one of the company’s mosquitoes could cause unusual reactions. However, both Oxitec and the EPA say the company is only releasing male mosquitoes, which lack the mouthparts to bite. Furthermore, in interviews with TIME, some on the anti-Oxitec side have thrown around baseless implications about Oxitec mosquitoes spreading herpes and Ebola.

Still, more valid scientific criticisms abound. Jennifer Kuzma, a professor of public and international affairs at North Carolina State University, says Oxitec’s technology should have been assessed by an external scientific panel during the EPA’s review. “This technology is meant to, in essence, spread through the ecosystem,” says Kuzma. “That…would have warranted a more rigorous and inclusive process of oversight.” Oxitec representatives say the EPA typically doesn’t assemble such panels for pesticidal products; for example, the agency didn’t do so when it approved a bacteria to fight mosquitoes in 2017. Moreover, some experts say that Oxitec’s technology has a smaller ecological footprint than spraying pesticides, which can harm beneficial insect populations. “This mosquito is an invasive species,” says Anthony James, a professor of microbiology at the University of California Irvine who specializes in genetic research on mosquitoes. “Any effort to get it out of the environment is not likely to have a significant ecological impact.”

Dr. John Norris, the chief of staff of the Lower Keys Medical Center, a hospital in Key West, worries that raising mosquitoes in the presence of an antibiotic—as Oxitec’s are—could promote the growth of antibiotic-resistant bacteria. “Are they pouring gasoline on one public health nightmare to deal with another one?” Norris says. Three outside specialists contacted by TIME were split on the merit of Norris’ concern. Oxitec representatives say the eggs that hatch in the U.S. never come into contact with the antibiotic, and that the EPA looked into the potential issue and found there was no risk.

Finally, Jeffrey Powell, an evolutionary biologist at Yale who studies mosquito genetics argues that, whatever the other environmental and health concerns, Oxitec’s technology basically doesn’t work. Powell shared data with TIME from a 2013-15 Oxitec trial in Brazil, which he says show the males’ effectiveness decreased after about a year and a half, because, he argues, females were beginning to stop mating with Oxitec’s modified males. “Even though the releases were continuing, and they were still doing like half a million mosquitoes a week, the population came back,” Powell says. Asked if this sort of issue may be of concern, Frandsen, the company CEO, offered a one word response: “No.” In an additional follow-up, the Oxitec representatives said that Powell’s assertion contradicts published data on the project, which show that mosquito populations remained suppressed for weeks after GM mosquito releases stopped.

The night before Oxitec announced the start of its Florida project, tourists filled outdoor bars and restaurants in downtown Key West, the buoyant atmosphere offering little hint at the momentous genetic experiment that was about to begin just a few miles away. Yet some locals aware of the project were still nursing a lingering sense of injustice. “Why do they have the right to experiment in the Florida Keys?” says Russo, as a band played a Frankie Valli cover from a bar across the street. “If they can do that, then I don’t know—I live in a different country…You be the judge. Is that the world you want to live in?”

Oxitec’s opponents aren’t giving up; some are considering lawsuits. “Even if we lost this battle, and we’ll have this shit in our environment, I still want to fuck them up,” says Daly.

Worldwide, mosquitoes and the diseases they transmit aren’t giving up either, and there is no question that we need solutions. You’re unlikely to be the target of a bobbing, weaving attack from an Aedes aegypti in New York’s Times Square or Chicago’s Millennium Park today, but in 2050, you just might find yourself brushing one of those tiny, deadly dancers off your shoulder. And as local opponents contemplate their next move, Oxitec’s vision of the future is beginning to crawl out of boxes across the Keys. If the company succeeds there, its genetically-modified mosquitoes would be one step closer to finding their way across the U.S. and the world, potentially becoming a key weapon in the global fight against mosquito-borne disease. “I just want to demonstrate the effectiveness of this technology,” says Frandsen. “We were given a shot. I want to prove it.”