US regulators on Friday moved one step closer to allowing a British company to introduce genetically modified mosquitoes in Florida — in what would be the first such release in the country — to test whether the approach could reduce the spread of dengue and chikungunya virus.

If the field test, in the Florida Keys, is successful, it would offer a proof-of-principle that genetic techniques might also slow the spread of the Zika virus as well as insect-borne diseases, such as malaria, that can sometimes be lethal.

The US Food and Drug Administration issued a “preliminary finding” that the genetically modified insects, produced by Oxitec at its labs in Oxford, England, and shipped as eggs to Florida, would have essentially “no significant impact” on human health, animal health, or the ecosystem. The public can submit comments on that conclusion for the next 30 days.

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Entomologist Phil Lounibos of the University of Florida, who has followed Oxitec’s proposal for years, said he was “not too surprised” by the agency’s conclusion. “FDA had dawdled for too long on this decision but Zika’s arrival helped to expedite Oxitec’s case.”

Oxitec’s Aedes aegypti mosquitoes have been genetically engineered to carry two foreign genes. One makes them die if they are not exposed to the antibiotic tetracycline (as would be the case anywhere outside a lab). The other makes them glow red. All of the released mosquitoes would be male, and when they mate with native females their offspring would also die without tetracycline while they are still larvae or pupae.

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The field test Oxitec wants to run — in Key Haven, Fla. — would assess whether that actually happens and estimate how much the overall aegypti population is suppressed at the trial site compared with a control area. At the end of the trial, the genetically modified mosquitoes would die when they reach their natural lifespan (about two days), and natural aegypti “levels are expected to recover to pre-trial numbers,” the FDA concluded.

The proposed release has nevertheless stirred significant opposition among residents of the Florida Keys. Many have argued that they have not given their consent to be at the epicenter of such an experiment, and a petition to “Say No” has acquired 161,000 signatures.

A former nurse who organized the petition said the Oxitec field test amounts to a “clinical trial,” and that neither the company nor the FDA has received consent from the community that would be affected. “I don’t want my family or my community to be guinea pigs,” said Mila De Mier, who lives in nearby Key West. “I don’t know one single resident of Key Haven who is in favor of this. She vowed to continue the fight in the courts.

In a statement, Oxitec chief executive officer Hadyn Parry said the company is “pleased” that the FDA-led team has concluded the field test would pose no significant harm. “The Aedes aegypti mosquito represents a significant threat to human health, and in many countries has been spreading Zika, dengue and chikungunya viruses.” Current control methods reduce aegypti populations by only half, he said, “which is simply not enough. We look forward to this proposed trial and the potential to protect people from Aedes aegypti and the diseases it spreads.”

Oxitec has conducted similar trials in Brazil, Panama, and the Cayman Islands, reducing the populations of Aedes aegypti more than 90 percent, the company previously reported.

The FDA’s finding that the mosquitoes pose essentially no harm to people or human health in Florida rests on several details of Oxitec’s plan.

Almost all of the released mosquitoes would be male, and males do not bite. If there are any biting females, they are not expected to transmit the glowing-red protein or the tetracycline protein: “concentrations of these proteins in the saliva of [Oxitec] females are below the limit of detection.” The company’s studies, the FDA said, showed that even if any of the engineered proteins were transmitted to people “there was no convincing evidence” it would be toxic or trigger an allergic reaction.

As for the ecosystem, the FDA concluded that the chance of any adverse effects “is largely negligible.” That’s because aegypti mosquitoes are not the sole food source of any animal, nor are they a pollinator for any plants. And when the proposed test is done, the population of aegypti is expected to rebound to its previous level — at least until and unless the test is deemed so successful, safe, and necessary that Oxitec is permitted to move from experiment to full-scale release.