If the federal Food and Drug Administration gives the go-ahead, Key Haven, Fla., would become the focal point of the first U.S. release of several million mosquitoes genetically altered by Oxitec, a British biotechnology company.

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KEY HAVEN, Fla. — In the bite-size community of Key Haven, like so many other mosquito-plagued spots up and down the Florida Keys, residents long ago made peace with insecticides dropped into town by planes or rumbling by on trucks. Cans of Off! are offered at outdoor parties. Patio screens are greeted with relief.

Keys residents are far less enamored of another approach to mosquito control: a proposal to release the nation’s first genetically modified mosquitoes, hatched in a lab and pumped with synthetic DNA to try to combat two painful, mosquito-borne viral diseases, dengue and chikungunya.

If the federal Food and Drug Administration (FDA) gives the go-ahead for the trial, Key Haven, with 444 houses built on a tiny peninsula, would become the focal point of the first U.S. release of several million mosquitoes genetically altered by Oxitec, a British biotechnology company.

Dangerous insects

The virus-carrying Aedes aegypti mosquitoes are difficult to kill and snack on humans almost exclusively. The Keys mosquito agency, regarded as one of the best in the country, can kill only 50 percent. Aegypti make up 1 percent of the Keys mosquito population but require 10 percent of the budget. The aegypti prefer urban settings. They love backyards, bite during the day and easily breed in tiny spaces — soda-bottle caps, for example. Insecticides, which can harm other organisms, often miss them. Only the females bite, which is how diseases are transmitted.

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For residents of a chain of islands notorious for their renegade spirit — nearby Key West once jokingly broke away from the United States as the Conch Republic — this possibility is fraught with suspicion and indignation.

“This is the first time they are releasing genetically modified mosquitoes in the country, and we have not given our consent,” said Mila de Mier, a Key West resident and real-estate agent who helped spearhead a four-year campaign to block the trial until more research is conducted. “People can’t be experimented on without their consent. When the mosquitoes are released, there is no way to recall it.”

The field release is subject to FDA approval. But the proposal has set off a chain reaction of anxiety and protest that began in 2011 and has gathered steam as the agency’s decision approaches.

In 2012, the Key West City Commission passed a resolution objecting to the release of several million genetically modified mosquitoes there. But Key Haven is about a mile away in unincorporated Monroe County.

Opponents continue to push back hard in gatherings and town-hall meetings, peppering scientists with questions. An online petition by de Mier to stop the release of the mosquitoes has drawn more than 149,000 signatures. To keep the campaign going, residents recently sent 1,600 emails to the Florida Keys Mosquito Control District, run by an independently elected commission.

“We feel it’s being jammed down our throats, and we are not getting answers,” said Beth Eliot, a Key Haven real-estate agent who said no one she knows supports the project. “The company that is saying that this is all safe is the company that stands to profit.”

Goal: fewer mosquitoes

Oxitec has made significant progress toward securing permission for the trial: Late last year, it got approval from several federal agencies to import mosquito eggs and build a lab for inspection. In the lab, scientists plan to inject the eggs with synthetic DNA and rear the mosquitoes, then release them in Key Haven, once the field trial is permitted. The lab is in the Marathon office of the mosquito-control district, which is working with Oxitec on the project.

Oxitec seeks to drastically reduce the population of the dangerous and hard-to-kill Aedes aegypti by freeing male mosquitoes with a specially made gene designed to kill their offspring after they mate in the wild. This, in turn, could blunt the spread of dengue and chikungunya, viral diseases that have no cure and are spreading quickly around the world.

For Oxitec, the Key Haven trial would be just one of several.

More than 70 million Oxitec mosquitoes have been released in field trials in the Cayman Islands, Malaysia, Brazil and, most recently, Panama, all of which have struggled with dengue. Regulatory agencies in those countries approved the release of mosquitoes, and last year Oxitec received approval from Brazil to commercially release its mosquitoes.

Trying to unleash a better weapon to curb dengue, which hit Key West in 2009 and 2010, and chikungunya is a smart preventive, said Michael Doyle, executive director of the mosquito-control district, which invited Oxitec to conduct the trial.

“Using the mosquitoes against themselves avoids two of the biggest problems: first, how to get the right chemicals to the elusive mosquitoes without causing collateral damage to beneficial animals,” Doyle said. “And second, how to find and repeatedly remove the thousands upon thousands of breeding spots that people unintentionally create all around our homes.”

Reports and statements by Oxitec and its academic and governmental collaborators say trials have reduced mosquitoes in targeted areas by an average 90 percent. Individual results vary. In two Brazilian villages, reductions were 60 percent to 70 percent, said Danilo Carvalho, a biologist at the University of São Paulo.

But critics say Keys residents are being used as guinea pigs even though the area does not have a dengue problem. They say questions persist despite numerous meetings with mosquito officials and scientists.

What happens if a person is bitten by a stray female mosquito (Oxitec said a tiny percentage get mixed in the release batch)? Nothing, Oxitec scientists say. What happens to the environment once the mosquitoes are introduced? Nothing, Oxitec scientists say. Who will be liable if something goes wrong with the mosquitoes? Oxitec, if a problem is caused by its actions or inaction, a company spokeswoman said.

“Based on the trials conducted, we’re confident that our mosquito is safe for humans and would do no harm to the environment, as were the regulators who approved its use,” said Chris Creese, Oxitec’s communications director.

In other words, the DNA dies with the mosquito, said Derric Nimmo, Oxitec’s project development manager.

“It is very species-specific,” Nimmo added.

Phil Lounibos, a University of Florida professor of ecology and behavior, said the risks, in general, were “very, very low.” But, he added: “We don’t know all the answers, and Oxitec could do a better job of explaining it.”

Others agree the danger is minimal.

“If there were mosquito genes coming into humans, we would know about it now because there are millions of mosquitoes biting humans every single day,” said Anthony James, a professor of microbiology and molecular genetics at the University of California, Irvine.