STOCK ISLAND, FLORIDA — Florida released thousands of bacteria-infected mosquitoes at a test site near Key West on Tuesday, hoping to stop the spread of Zika and other mosquito-borne viruses.

The Florida Keys Mosquito Control District released 20,000 mosquitoes infected with the Wolbachia bacteria at Stock Island, about 130 miles southwest of Miami, NBC News reported.

Wolbachia is a natural bacterium found in up to 60 percent of insects. However, it is not usually found in the Aedes aegypti mosquito, the main culprit for transmitting the Zika virus.

Scientists injected the bacteria into mosquito embryos. Wolbachia can stop viruses such as Zika from growing inside mosquitoes and is not harmful to humans.

Once infected, female mosquitoes spread the bacteria to their offspring, even if the female mates with an uninfected male. However, when an infected male mates with an uninfected female, the female’s eggs will not hatch.

The large-scale release of Wolbachia-infected mosquitoes has previously been trialed in South America. The method is recommended by the World Health Organization despite the absence of an official report on its impact.