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UF research team studies whether flies carry red tide toxins

Tons of dead fish lined the shores around Tampa Bay in the wake of this summer’s red tide, and those carcasses make great homes for flies. A University of Florida scientist wants to know whether flies can carry red tide toxins — known scientifically as brevetoxins — and if so, whether they can potentially harm humans or animals.

“Filth flies,” as Ted Burgess calls them, feed on garbage and dead matter.

“These flies are notorious for spreading pathogens,” said Burgess, an assistant professor of entomology with the University of Florida Institute of Food and Agricultural Sciences. “We are interested to know if these flies can also carry brevetoxins. If so, it would be a rare case of an insect carrying an environmentally derived neurotoxin.”

In this research, Burgess and his team will begin by asking: What role do filth flies play in the aftermath of mass-kill events caused by red tides?

“First, we hope to discover what types of filth flies are utilizing fish and other marine life that have succumbed to red tide poisoning and if the flies can act as a carrier of brevetoxins,” he said. “If they do carry the brevetoxin, why do they survive it when so many animals don’t?”

Burgess and his research team recently went to beaches around St. Petersburg to collect fish carcasses and flies, which they brought back to the UF campus in Gainesville for testing. The goal is to identify the types of flies found and, eventually, discover whether those flies can carry brevetoxin, the active neurotoxin that causes the widespread fish kills along the coast.

Tampa Bay provides the natural laboratory for part of an overall research project for Burgess, who wants to know which filth fly species utilize dead sea life after red tide events. While red tide killed tons of fish in Tampa Bay this summer, it can show up in many coastal areas of Florida, as it did in 2018.

It’s too early to know whether the flies from this year’s red tide in Tampa Bay can spread brevetoxin, Burgess said. But he and his research team are investigating.

“Brevetoxins do cause some adverse effects on people’s health, including respiratory and skin irritation when in close contact with the toxin,” he said. But Burgess cautioned that: “We are a long way from being able to tell if flies can carry enough brevetoxin inland from red tide-affected beaches that they begin affecting humans.”

“Filth flies eat and lay their eggs in organic matter, such as rotting vegetables or meat that you might find in garbage,” Burgess said. Some prefer to use the decaying flesh of dead animals for food and larval habitat. Other flies prefer to eat and lay eggs in rotting vegetation, animal feed and/or animal excrement.

Fish, horseshoe crabs and birds are especially sensitive to Karenia brevis — the species of algae that causes a red tide — and make up a significant portion of the victims of red tides. Filth flies seem to be able to develop in the dead tissues of poisoned animals.

If you want to know more about the flies and red tide, contact Burgess at edwinburgess@ufl.edu

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The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is to develop knowledge relevant to agricultural, human and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions to the state’s agricultural and natural resources industries, and all Florida residents.

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