FDA OKs first GM mosquito trial in U.S. but hurdles remain

No significant impact on health, environment foreseen from release of engineered Ae. aegypti in Florida

GMO mosquito

FDA OK'S GM TEST  The first test release of GM mosquitoes in the United States (adult males grown from larvae like these) will probably have no significant impact on the environment in Key Haven, Fla., the U.S. Food and Drug Administration has announced.


For the first time in the United States, free-flying genetically modified mosquitoes have federal approval to take wing in Florida. But when, and if, that will happen is still up in the air. Local officials will make the final decision — possibly not until after the November elections.

The World Health Organization has recognized these mosquitoes as possible tools for fighting the spread of mosquito-borne Zika virus. But the U.S. Food and Drug Administration’s decision, announced August 5, covers only a specific, preliminary test release of GM mosquitoes on Key Haven in the Florida Keys, where no locally transmitted Zika cases have been reported.

This trial of OX513A mosquitoes, genetically engineered by the British company Oxitec, “would be unlikely to result in adverse effects on the environment or human health,” the FDA ruled. If Key West commissioners approve it, the trial would release abundant GM male Aedes aegypti species carrying a gene that will cause their offspring to die. In tests in Brazil, Panama and the Cayman Islands, months of releasing these mosquitoes has reduced the wild populations of Ae. aegypti mosquitoes by 90 percent or more. As a result, a Brazil neighborhood has seen mosquito-borne dengue cases plummet (SNOnline: 7/15/16).

To see whether OX513A could work in the United States, too, the test release would now need approval from the Florida Keys Mosquito Control District Board of Commissioners. Opponents of GM organisms have protested the idea, so the five commissioners have arranged for a nonbinding referendum question to appear on the November ballot. Commissioners plan to wait until the community has weighed in before making their final decision, says mosquito control district spokeswoman Beth Ranson.

If the mosquito plan gets a thumbs up, Oxitec could release mosquitoes in December, said Hadyn Parry, the company’s chief executive officer. Monitoring and testing could take six months and results would go back to the FDA with an application to allow the mosquitoes to be released commercially — and more broadly — in the United States for mosquito control.

As Zika rages in Puerto Rico, and with Miami reporting the first locally mosquito-transmitted cases on the U.S. mainland, debate over the controversial mosquito has taken on new urgency. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, has noted that efforts to eradicate mosquitoes in an area in Miami have fallen short (SNOnline: 8/1/16).

Ae. aegypti mosquitoes resist many pesticides, bite during the day, love human houses, and can breed in plant saucers and other small pools of water. Virtually a domestic animal, this species bites people almost exclusively. It’s suspected to be the main spreader of Zika virus, and also does a fine job of infecting people with dengue, chikungunya and yellow fever viruses.

Oxitec GM mosquitoes, developed in 2002, would target Floridian pests via a new twist in the decades-old strategy of male sterilization. Mid-20th century entomologists sterilized screwworms by irradiating them and releasing the decoy males in overwhelming clouds. So many wild females mated with these sterile males that eventually the gruesome screwworm pests of livestock disappeared from the United States.

OX513A, with their mix of old-fashioned strategy and newfangled genetic tinkering, has kicked up anti-GMO feeling, even though it’s not the first U.S. approval of testing a GM insect in pest control. That honor goes to pink bollworms in the Southwest in 2009, though their release passed largely unnoticed outside the pest-control community. But when the FDA released a favorable draft opinion in March, saying the GM-mosquito test would probably have “no significant impact” on people or the environment, more than 2,000 people typed comments on the public FDA site. Many were vehemently opposed to the plan, peppering their comments with multiple exclamation points and the occasional “OMG!!!”

Some commenters worried about blood contact from the bite of a GM organism, possible allergies should someone accidentally swallow one and unknown consequences to the environment. 

Oxitec posted explanations responding to those fears: Almost all mosquitoes released would be males, which don’t bite; males will die three or four days after release; their offspring are engineered to die without unnatural amounts of tetracycline — a lab-provided supplement — in their diets. Angry public comments, however, largely dismissed these reassurances as corporate-funded research.

Another commenter wondered whether a successful test, driving down the Ae. aegypti population on the Keys, could make room for some other insect menace. That’s a reasonable question, says Phil Lounibos of the University of Florida in Vero Beach. He has studied competition between Ae. aegypti and the relentlessly biting Asian tiger mosquito, Aedes albopictus. These tiger mosquitoes were once rare on the Keys, but he has found that they can take over from Ae. aegypti, in part by sexual deception. Tigers that mate with Ae. aegypti females render the females sterile and have thus conquered other parts of Florida. Even though Ae. aegypti is recognized as a more potent vector for human disease, the tigers can carry many of the same viruses (including Zika), Lounibos warns (SNOnline: 5/16/16).

As far as ecological concerns go, entomologist Bruce Tabashnik of the University of Arizona in Tucson, has no problem with eradicating Ae. aegypti from the Florida Keys or anywhere else in the Americas. “It’s an invasive species,” he says. “There are no ecological ethics violated.”

Tabashnik was part of the research team monitoring the first GM insect release in the United States: sterile male pink bollworms. Males of this invasive pest species that prey on cotton in the Southwest were sterilized by radiation. However, Oxitec had inserted a gene that made them fluoresce red so monitors could tell the friendlies from the wild targets. Tabashnik recalls no particular public outcry over the experiment. It took place in a sparsely populated area and, instead of mosquitoes, involved a kind of moth only a cotton farmer could hate.

So far outrage, or even interest, in other tweaked pest-control animals seems minimal compared with GM-mosquito fever. A proposed test of Oxitec’s GM diamondback moth in New York has inspired fewer comments. Tests of a non-GM but still tinkered-with mosquito — Ae. albopictus developed to carry Wolbachia bacteria that interfere with mating — were first approved in 2012 for release in American Samoa. Later tests have released these bacteria-carrying mosquitoes in California and other sites in the mainland United States. 

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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