In the coming weeks, swarms of sterile screwworm flies will blanket parts of the Lower Keys, an army of millions manufactured in Panama to combat an outbreak of the flesh-eating pest attacking the islands’ beloved Key deer.
The flies, used to protect domestic livestock over the decades, represent the best hope at stopping infections that have so far killed 117 deer, or about a tenth of the herd.
Everyone is watching very closely because of the seriousness of this outbreak.
Florida Agriculture Commissioner Adam Putnam
“Everyone is watching very closely because of the seriousness of this outbreak and the seriousness of the implications to the American livestock industry,” Florida Agriculture Commissioner Adam Putnam said Thursday after traveling to Big Pine Key, which has come under national scrutiny. “If this were in another state, I would be watching it very closely.”
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Since Oct. 11, about two weeks after the infestation was confirmed in deer at the National Key Deer Refuge, 10 million flies have been released at 25 locations, from No Name Key west to Cudjoe Key. The outbreak is the first significant infestation in the U.S. in more than three decades and the first to be treated in a wild herd.
The stakes are even higher because the herd of dog-sized deer is the planet’s last.
The outbreak also comes at a time when Florida seems to be awash in pestilence, from Zika-carrying mosquitoes to fungus-spreading beetles killing avocado trees.
“Unfortunately, this is all too common in our subtropical climate that is home to a lot of international cargo and passenger travel,” Putnam said.
On Friday, the U.S. Department of Agriculture plans to up the number to 13 million flies. The agency plans to continue releasing 6 million per week, but that number will likely change as more infected deer are found, an agency spokeswoman said.
U.S. Fish and Wildlife vets are also trying to inoculate sick deer by treating them with an anti-parasitic. Rangers and dozens of volunteers trained over the weekend have begun feeding the deer — mostly bucks wounded during the Fall rutting season —with treated bread then marking them with paint to track treatments. Vets for the first time also have started tracking wild deer in the refuge, beginning with four males Wednesday night. Because the deer are so skittish, vets are sedating them, removing larva from wounds and applying a topical anti-parasitic that should last 30 days, said spokesman Kevin Lowry. They also are tagging antlers and shaving numbers in their fur so they can better identify wild animals that have already been treated.
Biologists are also keeping watch for infections in other wildlife, including endangered marsh rabbits and woodrats.
The issue with the small animals is they will die in two to four days.
National Key Deer Refuge biologist Adam Emerick
“The issue with the small animals is they will die in two to four days,” said refuge biologist Adam Emerick. “The tissue damage is very rapid.”
So far, sick deer have been found on Big Pine and No Name keys. A sick deer was found on Sugarloaf Tuesday and euthanized, but the infection has not yet been confirmed, Lowry said.
Despite the large number of flies, residents won’t likely notice the insects being released in wooded hammocks — where wild flies breed — because they don’t fly far. On Thursday, John Welch, a USDA entomologist based in Texas who has investigated screwworm outbreaks across the Caribbean and the Americas, and Orlando Pitti, who oversees fly breeding at the Panamanian lab jointly run with the U.S., led Putnam and a gaggle of reporters into a soggy hardwood hammock near Big Pine Key Fishing Lodge to demonstrate the releases.
Pupae, raised on a “pudding” made from powdered blood, milk, eggs and cellulose, are being flown, chilled, from Panama twice weekly, Welch said. About 78,000 are spread on trays in each box — green crates slightly larger than a milk crate — and strung from trees. Over 24 and 48 hours, the iridescent blue flies hatch. While it’s not known how long it will take to wipe out the wild flies, past treatments succeeded after two to three life cycles, he said.
Scientists are using satellite imagery of the islands to find woodsy spots where flies likely breed, then picking locations near sick deer. However, because wilder deer may die unnoticed in thick brush, entomologists are also searching for wild flies, a tricky and slightly gross process that involves using liver to trap the elusive flies.
A thornier matter will be determining where the flies originated. Days after the outbreak was confirmed, Welch said entomologists collected larvae and sent them to the Panama lab, where a colony will be reared and compared to frozen screwworms collected during other outbreaks.
“We’ll develop a profile and then compare it to other known populations and we may not be able to say,” he said. “We have to wait and see.”
An earlier version of this story incorrectly said sterile flies will be released in the Middle Keys. The releases will occur in parts of the Lower Keys. The USDA also revised the number of estimated flies released to 6 million per week.
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