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satellite image of Key Haven, Florida

The island suburb of Key Haven, Florida, is the proposed site of Oxitec’s first U.S. release of genetically modified mosquitoes.

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Update: Florida voters split on releasing GM mosquitoes

UPDATE:  Although 57% of residents of Monroe County in Florida voted in favor of releasing transgenic mosquitoes produced by Oxitec, the fate of the company’s trial there is unclear. In the small suburb of Key Haven, the proposed site of the trial, 65% of the 643 residents who voted were against the release. Although both of these referenda were nonbinding, three of five members on the local mosquito control board have said they would follow the decision of the voters on whether to approve the project. It’s not yet clear what the split vote means for their decision, but the board is expected to discuss next steps at its 19 November meeting.

“While we did not win over every community in the Keys, Oxitec appreciates the support received from the community, and is prepared to take the next steps with the Florida Keys Mosquito Control Board to trial its environmentally friendly and nonpersisting mosquito control solution,” Oxitec CEO Hadyn Parry said in a statement.

Here is our previous story:

Voters on the tiny suburban peninsula of Key Haven, Florida, will find an unusual question on their ballot on Election Day:

“Are you in favor of the Florida Keys Mosquito Control District conducting an effectiveness trial in Key Haven using genetically modified mosquitoes to suppress an invasive mosquito that carries mosquito-borne diseases?”

Behind that question is a ferocious debate about the first proposed release of genetically modified (GM) mosquitoes in the United States. The biotech company Oxitec designed the mosquitoes to carry a gene that causes their offspring to accumulate a toxic protein and die before adulthood, which could reduce populations of the Aedes aegypti mosquito that transmit the dengue, Zika, and chikungunya viruses.

The U.S. Food and Drug Administration (FDA) greenlighted the project in August, but local opposition has been so strong that the mosquito control board has held off on approving the release. The ballot referenda—one for Key Haven and another for the broader Monroe County—are nonbinding. But three of the five board members have said they will follow the voters’ decision. Oxitec has been releasing mosquitoes in other countries since 2009; the Cayman Islands, Malaysia, Brazil, and Panama have all hosted field experiments, and the company has reported greater than 90% reductions in mosquito populations in small test areas. But we don’t know everything about the mosquitoes or their potential impact. Here’s what the evidence says so far about some concerns Florida residents and mosquito experts have raised.

Could a GM mosquito bite a Floridian?

It’s possible. Oxitec aims to release only males, which don’t bite, but its sorting system isn’t perfect. The company says it ensures that a maximum of 0.2% of the mosquitoes released are female. Over the proposed 26-month trial, that works out to fewer than 62 females mosquitoes per person in Key Haven—2.4 mosquitoes per household per week. (Of course, it’s hard to predict how many of them will actually alight on some human skin.)

Could a GM mosquito transfer genes to a human, or make them sick?

It’s highly unlikely. As the agency’s environmental impact document puts it, “mosquitoes have been feeding on humans and other animals for millennia but there is no evidence of DNA transfer between mosquitoes and humans.” There’s also “negligible” risk that the GM mosquito saliva would have any toxic or allergenic effects on humans. The two unique proteins it carries—the lethal one that affects gene transcription and a fluorescent protein to distinguish it from wild mosquitoes—were undetectable in the insects’ saliva. If they’re in there, the levels are likely too low to affect us, FDA concluded.

Could genes from the Oxitec strain spread to the wild mosquitoes?

Yes. In lab experiments, Oxitec’s lethal gene isn’t 100% lethal. The company has reported that about 4% of offspring survived to become flying adults. That survival rate might be lower in the wild, but if the offspring live long enough and are healthy enough to mate, they will introduce genes from the lab strain into the wild population. 

“That’s something that does have to be paid close attention to,” says entomologist Zach Adelman of Texas A&M University in College Station. When Oxitec stops its releases, mosquito numbers will rebound, and it is not clear whether or how the genes from the release strain would influence the recovered population, including how mosquitos seek out hosts, mate, or lay eggs, for example. Of key concern, he says, is how good Oxitec’s strain is at transmitting viruses compared with wild mosquitoes—its so-called vector competence. So far, studies of such changes in a postrelease population are missing, Adelman says.

Simon Warner, Oxitec’s chief scientific officer in Abingdon, U.K., says there’s no reason to think their lab strain—descendants of mosquitoes collected in Cuba, crossed with a Mexican strain—would be any more dangerous than another strain of A. aegypti. “Vector competence is not a question that we’ve been asked by the [FDA] regulators,” he says. “We haven’t studied it, because we don’t think it’s a concern.”

Could mosquitoes become resistant to the Oxitec strategy?

Yes, if surviving larvae carried genetic variants that protected them from Oxitec’s lethal gene. For example, if a mosquito happened to inherit genes that prevent the lethal protein from accumulating in its body, or that allow it to survive high levels of the protein, these traits could get selected for over generations. That could mean that in the future, Oxitec’s releases would make less of a dent in the population. That scenario is a “theoretical possibility,” says insect geneticist Max Scott of North Carolina State University in Raleigh, but “it wouldn’t stop me from going ahead and testing it in Florida, because I think this is a very useful technology.”