By CAROL RYAN DUMAS
TWIN FALLS COUNTY, Idaho -- Black flies, also known as buffalo gnats, are annoying to people, but they are a serious pest for livestock, reducing weight gain and transmitting disease.
Ranchers in the area have had problems with black flies over the years but are now seeing successful black fly control through the efforts of the Twin Falls County Pest Abatement District, sheep producer John Noh said.
The flies pester livestock, causing them to bunch together and not want to eat, drink or move, he said.
The flies also led to an outbreak of vesicular stomatitis in Idaho livestock in 2005, resulting in quarantines and lost production.
The Snake River and 2,000 miles of irrigation canals and laterals in the county offer ideal habitat for the pests, said Kirk Tubbs, manager of the Twin Falls County Pest Abatement District.
The black fly larvae require moving water to survive to the adult stage, and the Snake River is one of the largest overwintering habitats in the area.
Each female can lay up to 600 eggs, which can hatch and develop in as little as seven to 10 days.
Huge populations can develop very quickly. One billion black flies per mile of river or canal can hatch in one day, Tubbs said.
In addition, adults can travel 25 to 30 miles looking for new homes, making control difficult as adults can immigrate to the area from other untreated areas, he said.
Twin Falls County is the only one in Idaho to treat for black flies. Now in its fourth year, it's had a lot of success, he said.
The county treats the river during the winter months for overwintering black fly larvae, reducing the number of black flies that would otherwise hatch and colonize canals when water begins to flow in the spring. It also treats the river and irrigation canal system in the summer.
"The challenge is we're only treating Twin Falls County and last winter couldn't afford to treat the river," he said.
That's because of an exceptional water year that had river managers raising the flows to release water from full reservoirs. The abatement district treats by volume of water, and didn't have the budget to treat so much water, he said.
The county spends $180,000 a year on a commercial insecticide, derived from a natural soil bacterium, that is harmless to humans, fish and livestock.