In a 3-2 vote on Saturday, the Florida Keys Mosquito Control District approved a trial of genetically modified mosquitoes designed to curb the spread of infectious diseases, such as Zika, dengue, and chikungunya.

The vote was one of the last remaining hurdles for the bugs, which in August became the first GM animals to win approval from the Food and Drug Administration for use in an open field trial. However, local opposition to the long-planned trial remains fierce, and officials still have more work to do—including finding a new trial site.

In two November 8 ballot measures, Key West residents revealed split feelings on the mosquitoes. In Monroe County, 58 percent of residents approved of the trial. But in Key Haven, a small community within Monroe county where the trial was set to take place, 65 percent opposed it. Afterward, Phil Goodman, chairman of the district’s board of commissioners, said that if the board moved forward with the trial, it would find a new site due to Key Haven's opposition.

Key Haven residents have explained that they don’t want to be used as “guinea pigs” and fear unintentional environmental consequences. Some also fear being bitten by engineered blood-suckers. However, the FDA and other federal and local regulators say the concerns are unfounded.

The trial involves Aedes aegypti mosquitoes that have been engineered by the British biotech company, Oxitec, to pass on lethal genetics. A. aegypti are exotic and invasive to the United States, including Florida. Only females can bite, and they're able to transmit viruses, such as Zika. To knock back the bugs, Oxitec plans to release millions of engineered males—which naturally don’t bite—to mate with wild females and produce dud offspring. In similar trials in Panama and Brazil, the engineered mosquitoes were able to zap up to 90 percent of wild populations for short periods.

Because Oxitec will release so many mosquitoes, there’s a chance a small number of biting females may slip through. However, they wouldn’t transmit genetic modifications or be any more dangerous than a typical mosquito.

Despite the unfounded fears, officials in Florida are left searching for a new site for the trial. At the Florida Keys Mosquito Control District’s meeting yesterday, a woman from Key Largo (also part of Monroe County) threatened that residents would purposefully kill any GM mosquitoes if the trial were to take place there. “Have fun with that,” she warned the board, according to STAT.

The board will need to get new FDA approval to change the trial site location.

The forward movement on the trial comes on the heels of the World Health Organization’s announcement that the spread of Zika is no longer an emergency, but rather a long-term public health threat.