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Mosquito spraying temporarily stops on Big Pine

A pair of potentially endangered butterfly species have Big Pine Key residents concerned about the prevalence of a different insect altogether.

The U.S. Fish and Wildlife Service, which oversees the National Key Deer Refuge on Big Pine, put a halt to the Florida Keys Mosquito Control District spraying adulticide on the island in mid-June so it could monitor dwindling Bartram's hairstreak and Florida leafwing population. Both are candidates for the Endangered Species List.

That means the district has been unable to use its spray trucks -- familiar sites to most Keys residents -- to patrol Big Pine neighborhoods since then. The adulticide is dispensed as a fog from the trucks.

"In past years, Mosquito Control has worked with us to get a special-use permit, and with the potential for listing these two species [as endangered], there was a request to do a conference opinion," refuge Manager Nancy Finley said. "It's about determining how to minimize the adverse affect to the organism; that includes making sure its habitat aren't affected."

Part of that is determining how much, if any, adulticide drifts onto the croton plant on which both species depend for survival. Croton is a small, low-lying shrub.

"It's the sole source plant for these butterflies," Finley said.

Finley said Fish and Wildlife studies have determined that Bartram's hairstreaks, once common throughout the state, are only found on Big Pine and on Long Pine Key, a tiny island in Everglades National Park. Its population is estimated at 100 to 800 adults total.

The Florida leafwing population is thought to be "several hundred or fewer." It's found in the Everglades, sporadically in Miami-Dade County and "may be gone from Big Pine.

Mosquito Control Director Michael Doyle said larviciding makes up 90 percent of how the district kills mosquitoes. Adulticiding is a back-up plan, but a useful and important one, he said.

Larvicide kills mosquito larvae in the water before they fly, while adulticide kills adult mosquitoes with a fine mist at night or early in the morning. District aircraft dispense many tons of larvicide granules up and down the Keys.

"Over the Fourth of July weekend, we put out 17,000 pounds," Doyle said.

Doyle said adulticide used by the district is a "general low-level insecticide toxin" meant to kill mosquitoes and smaller insects. It's not meant to affect larger insects like butterflies.

"It's been approved by the [U.S. Environmental Protection Agency] for use in mosquito control, but [Fish and Wildlife's] view is anything that could possibly affect these endangered species, they want to restrict," Doyle said.

Finley said the district and Fish and Wildlife are working together to get Mosquito Control spray trucks running again. The district provided information Tuesday that Finley said would be analyzed in Vero Beach.

"They've done a great job getting information to us," she said. "They have hundreds of them to do, but based on the urgency and the community concerns, we'd want to expedite. Hopefully it could be a couple of days."

In the meantime, Doyle said the district has been ramping up larviciding on offshore islands that are fertile breeding grounds for mosquitoes.