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“The public resistance and the need to reach some agreement between mosquito control and the public — I see that as a very significant issue, outside of the (operating) costs, since this is not just a one-time thing,” Mr. Lounibos said.

The Aedes aegypti has shown resistance to pesticides used to control other species and is the most difficult for the district to manage. Common in the Southeast and the Caribbean, it lurks in standing water around houses and businesses and can breed in containers as small as bottle caps.

District inspectors go door to door to remove the standing water where they breed, a time-consuming task. The district spends roughly $1 million a year to suppress Aedes aegypti, 10 to 15 percent of the agency’s budget, Mr. Doyle said.

“Unfortunately, control of Aedes aegypti is a never-ending job,” said Larry Hriber, the mosquito control district’s research director.

In the trial, thousands of male mosquitoes bred by Oxitec would be released in a handful of Key West blocks where the Aedes aegypti is known to breed; the number of mosquitoes in those neighborhoods would be measured against the numbers from similar blocks where no modified mosquitoes were released.

The state’s agriculture department oversees the mosquito control district, and Mr. Doyle said he would not expect any challenge from the state if the FDA signed off on the trial. The mosquito control district wouldn’t need any local permit for the trial, either, but officials held a public meeting earlier this year and have posted information on the agency’s website.

Still, it could take years for the FDA to approve the trial.

There hasn’t been a case of dengue fever in Key West since November 2010, but two other cases were reported elsewhere in South Florida this fall.

The mosquito trial proposed for Key West wouldn’t be the first release of genetically modified insects in the U.S.

In 2009, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service concluded that integrating genetically modified pink bollworms, bred by Oxitec to be sterile but more competitive in mating than regular bollworms, into the agency’s plant pest control program was “the environmentally preferable alternative” to combat the cotton pest. The program was discontinued, however, after officials found that the genetically modified insects were not as hardy as pink bollworms sterilized through irradiation and that their use would cause farmers to lose their organic certification.

Oxitec said the USDA’s environmental assessment is one of several examples of proof that the trial’s risks and methods are being independently evaluated. The company has trials in Brazil, the Cayman Islands and Malaysia, and it says it’s gotten positive reviews from the latter two governments. It also cites its published research in peer-reviewed journals.

But Mr. Biddle, the onetime dengue patient, wants Oxitec to continue testing the modified mosquitoes outside the U.S.

“Why the rush here?” the Key West man said. “We already have test cases in the world where we can watch what is happening and make the best studies, because wouldn’t it be wonderful if we could find out how it can be fail-safe — which it is not right now. It’s an open Pandora’s box.”