KEY WEST, Florida (AP) ― Millions of genetically modified mosquitoes could be released in the Florida Keys if British researchers win approval to use the bugs against two extremely painful viral diseases.

Never before have insects with modified DNA come so close to being set loose in a residential U.S. neighborhood.

“This is essentially using a mosquito as a drug to cure disease,” said Michael Doyle, executive director of the Florida Keys Mosquito Control District, which is waiting to hear if the Food and Drug Administration will allow the experiment.

Dengue and chikungunya are growing threats in the U.S., but some people are more frightened at the thought of being bitten by a genetically modified organism. More than 130,000 people signed a Change.org petition against the experiment.

Even potential boosters say those responsible must do more to show that benefits outweigh the risks of breeding modified insects that could bite people.

“I think the science is fine, they definitely can kill mosquitoes, but the GMO issue still sticks as something of a thorny issue for the general public,” said Phil Lounibos, who studies mosquito control at the Florida Medical Entomology Laboratory.

Mosquito controllers say they’re running out of options. With climate change and globalization spreading tropical diseases farther from the equator, storm winds, cargo ships and humans carry these viruses to places like Key West, the southernmost U.S. city.

There are no vaccines or cures for dengue, known as “break-bone fever,” or chikungunya, so painful it causes contortions. U.S. cases remain rare.

Insecticides are sprayed year-round in the Keys’ charming and crowded neighborhoods. But Aedes aegypti, whose biting females spread these diseases, have evolved to resist four of the six insecticides used to kill them.

Enter Oxitec, a British biotech firm that patented a method of breeding Aedes aegypti with fragments of genes from the herpes simplex virus and E. coli bacteria as well as coral and cabbage.

This synthetic DNA is commonly used in laboratory science and is thought to pose no significant risks to other animals, but it kills mosquito larvae.

Oxitec’s lab workers manually remove modified females, aiming to release only males, which don’t bite for blood like females do. The modified males then mate with wild females whose offspring die, reducing the population.