Keys Test New Way To Eradicate Mosquitoes By Infecting Them With Bacteria

Jul 26, 2017

While mainland South Florida ramps up its battle against the mosquito that can carry Zika, the Florida Keys has already begun the region's most intensive mosquito control operation.

The nation's first trial of genetically modified mosquitoes received federal approval last year for a site in the Keys, but that test has been delayed after residents of the testing area voted against it. The company that makes the genetically modified mosquito has resubmitted its application to include the entire Florida Keys.

Meanwhile, another method to stop Aedes aegypti mosquitoes from breeding is getting its first Florida trial in the Keys. The Florida Keys Mosquito Control District is releasing male mosquitoes infected with the Wolbachia bacteria on Stock Island.

Three times a week, a UPS truck drops off a cardboard box at the district office. The box holds a Styrofoam cooler — which holds 25 cardboard tubes. Each tube holds 1,000 mosquitoes, which buzz audibly when their box is opened.

They come from a company in Kentucky called MosquitoMate. And they're all male — which means they don't bite.

Mosquito mission: Mate but don't reproduce

Their mission is to mate with female mosquitoes in the wild. They've been infected with Wolbachia, a bacteria that naturally occurs in a lot of insects, but not Aedes aegypti.

"When these males are infected and they mate with the females, it results in sterility," said Catherine Pruszynski, a research biologist with the Keys mosquito control district.

The females that breed with the Wolbachia-infected males lay eggs, but there's no offspring.

"The eggs are just empty," Pruszynski said. "There's no larval development, no nothing."

Mainland South Florida saw hundreds of cases of Zika last year, with two areas of local transmission in Miami-Dade. The Keys only had a handful of cases, all travel-related.

"We're fortunate here that we have a world-class mosquito control district," said Bob Eadie, the county's health director.

Already on high alert

Monroe County was already on high alert about Aedes aegypti mosquitoes because Key West had a dengue fever outbreak in 2009, the first locally transmitted cases in the U.S. in decades. There were about 100 cases.

"It was troubling," Eadie said. "It's a very debilitating disease while you have it."

The Keys Mosquito Control District ramped up its efforts to eradicate Aedes aegypti then. Inspectors go house-to-house, checking for places mosquitoes might breed. Waking up to helicopters spraying larvicide over the island is a normal part of life in Key West.

In the Keys, the Mosquito Control District is an independently elected board with the ability to levy taxes. It has an annual budget of about $11 million — $142 for every resident of the Keys.

Low-tech operation

Releasing the test mosquitoes is a low-tech operation. Pruszynski walks along Maloney Avenue on Stock Island, a street lined with trailer parks and trapyards. She carries a bag with 10 tubes. She pulls out a tube, takes the end off and releases the mosquitoes.

Catherine Pruszynski, research biologist for the Florida Keys Mosquito Control District, encourages some reluctant male mosquitoes infected with Wolbachia to fly out into the wild.
Credit Nancy Klingener / WLRN

"They're probably going to make their way over to the lobster traps, to hide," Pruszynski says. Some of the mosquitoes are reluctant to leave their temporary home so she gently blows on the cardboard to send them on their way.

The trial site is 10 acres. There's a control site of 10 acres, with a buffer in between. Both sites receive exactly the same treatment and the district has not stopped its other mosquito control efforts during the trial.

There are mosquito traps in both areas, which are compared to see if the Wolbachia-infected mosquitoes are having an effect on the overall population. The trial was originally supposed to end in early July, but has been extended at least until the end of the month.