Residents of the Florida Keys headed to the polls on Tuesday to air their thoughts on genetically modified mosquitos—among other things.

On the ballots in Monroe County and the community of Key Haven, an island in the lower Florida Keys, was a question on a long-standing plan to release millions of mosquitos as part of a scientific trial. The mosquitos are genetically engineered to sabotage wild populations, which can transmit dengue, Zika, and other diseases.

The modified mosquitos have already won approval from the Centers for Disease Control and Prevention, the Food and Drug Administration, and the Environmental Protection Agency. But local opposition brought the issue to the ballot. On Tuesday, residents of Monroe County solidly voted in favor of the trial—58 percent of the around 40,000 voters. But in the approximately thousand-person community of Key Haven, where the trial is set to take place, 65 percent voted the trial down.

After the polls, Mila deMier, an organizer of the opposition to the trial in Key Haven, told Florida Health News: “I'm very happy for the people on Key Haven because they exercised their right not to be used as a guinea pig."

The mixed vote leaves open the question of what will happen to the trial plans. Both the county and the Key Haven ballot measures were nonbinding, and the final decision is now up to the Florida Keys Mosquito Control District, which will vote November 19.

"Obviously, we're very pleased about Monroe County," Derric Nimmo, chief science officer for Oxitec, the British biotechnology company that engineered the bugs, told Florida Health News.

Phil Goodman, chairman of the district’s board of commissioners, confirmed to Wired that the county’s approval was enough to move forward with the plans. “We’ll be looking at where mosquitos are, and come up with some other sites of where to release them based on where people voted yes,” he said.

That may not fly with Key Haven residents, though, who said they will oppose the trial regardless of its location. Their opposition stems from concern that the mosquitos could harm people and disturb wild insect populations.

Oxitec’s self-limiting genetically modified mosquitos are Aedes aegypti, an exotic invasive species to the area. The males, which don’t bite, pass on a lethal gene to offspring. Once released, they’re intended to mate with wild females and doom the next generation. Similar trials are already ongoing in other places, including the Cayman Islands, Brazil, and Panama.

Key West experienced a dengue outbreak in 2009 to 2010, but it has largely dodged Zika, despite large numbers of cases and some local transmission in nearby Miami-Dade County. Officials there said they're interested in pursuing the genetically modified mosquitos.