By Sharon Omahen
University of Georgia

When it comes to black flies, most people would prefer them destroyed. In the U.S., their bites cause pain and welts. In Africa, they can cause blindness. But to help find ways to control the tiny pests, University of Georgia scientists maintain the world’s only research colony.

Often described as gnats, black flies are small, dark, stout flies about half the size of mosquitoes. Like gnats, they swarm around people’s faces and eyes. The big difference is that their bites hurt.

Causes welts, blindness

“We’re spoiled in the South as our species doesn’t usually bite,” said Elmer Gray, a medical and veterinary entomologist with the UGA College of Agricultural and Environmental Sciences. “In Canada and northern states like Maine and Massachusetts, they bite and leave a bloody welt.”

In Africa, black flies carry a nematode that can move to the cornea of a bite victim and cause what is called river blindness. It affects 30 million people in Central and South Africa each year, Gray said.

To fight the fly, a bio-control agent called Bti, or Bacillus thuringiensis var. israelensis, was developed. "It's not a chemical pesticide,” he said, “so it doesn't pollute streams or damage water quality.”

Testing control formulations

Bti is a strain of a soil-dwelling bacteriuim that occurs naturally. It is considered safe to people and wildlife. The World Health Organization has approved it for drinking water treatment in some countries, he said.

With funding from Valent Biosciences, Gray and a team of 10 UGA students and technicians work every day, year-round to maintain the colony’s 2.7 million black flies. Keeping a healthy colony alive and thriving is an essential component of testing the Bti effectiveness in controlling the pest, he said.

Housed, fed and harvested

The researchers house the fly colony in Athens, Ga., in lobster tanks and modified salt water aquariums, a system developed at Cornell University to replicate a river habitat.

The fly colony is fed soybean meal and rabbit chow. “Our flies are larger than the flies found naturally in streams because they’re fed well,” Gray said.

Every Tuesday, the team harvests 18-day-old larvae to use to test Bti formulations. “Only 10 percent are used for research purposes,” he said, “but we have to keep a large population to ensure a healthy colony.”

Knowing how much Bti to apply to black fly populations will enable groups like the WHO to control the flies instead of treating people for the problems they cause, he said.

“Bti can be applied on a large scale using helicopters,” Gray said. “It typically costs about $25-27 a gallon in liquid form.”

Just the right amount

The UGA researchers are also working on Bti quality. “The particles have to be the right size and must be stable and disperse in water to be effective,” Gray said.

Flies from the UGA colony are being used by other UGA researchers and in research programs at Kansas State University, University of Alabama, Clemson University and Brock University in Canada.

“We share samples with anyone we can help,” Gray said.