OVERTON Encouraged by heavy rains and cool weather, black flies or buffalo gnats are emerging in record numbers from streams in central and eastern Texas, from College Station to Texarkana.
“It’s the worst I’ve seen in 10 years we’re talking about the potential of millions of dollars of damage to livestock owners, the paper manufacturing industry and tourism,” said Dr. James Robinson, an entomologist with the Texas Agricultural Extension Service.
Less than 1/8 inch long, the black fly lives only six to eight weeks as an adult, takes 10 minutes to drink half a drop of blood, and rarely flies at night.
Though individually tiny, in mass numbers the buffalo gnat has the power to drain the pockets of Texas livestock producers of hundreds of thousands of dollars when its larvae hatches and it emerges from rivers and streams in large numbers.
Each fly takes only a minuscule serving of blood, but thousands of servings add up, irritating animals and causing them to go off feed.
Paper mill managers also dread a heavy emergence of the fly. Millions of tiny flies invade the mills, finding their way into the paper-making machines, their bodies leaving minuscule black specks on freshly milled paper. During a year of heavy emergence, the black specks may ruin paper worth hundreds of thousands of dollars.
On recreational areas, the flies can turn a tourist’s outing or a fishing enthusiast’s excursion into a nightmare, Robinson noted.
Robinson has been comparing different controls of black flies since 1979. One thrust of his work has been to find the most effective, environmentally safe control for the insect.
Since the late 1980s, Robinson has recommended using Bacillus thuringiensis israelensis (Bti) in streams where the black fly larvae develops. Bti is a proven and highly effective and environmentally safe control, Robinson said. Very similar to compounds occurring naturally in Texas waterways, Bti is non-toxic to humans, amphibians, fish, crustaceans, adult insects, flatworms and mollusks. Neither is it toxic to insect predators of the black fly, such as dragonflies.
For all practical and economic purposes, it is impossible to completely eradicate an insect species such as the black fly. Every year, varying numbers emerge but most years, these emergences range from being inconvenient to mildly irritating for those who live and farm next to streams. When conditions are optimal, however, the flies emerge in large enough numbers to endanger livestock.
The optimum conditions came this year. With unseasonable rains and untimely temperatures during the late fall of 2000 and early 2001, conditions were perfect for the eggs to hatch and the larvae to survive.
County extension agents periodically surveyed streams in their area and tried to draw estimates of how severe the hatch would be from the number of larvae they find sticking to submerged twigs and branches. Large numbers have been found, but the swollen rivers would have required using large amounts of Bti, which would have been prohibitively expensive, Robinson said.
Livestock, poultry and pet owners may have to resort to the use of pesticides this year. The same insecticides labeled to control horn flies and stable flies on cattle and horses are also effective against adult black flies. Backyard flocks of poultry should be kept penned in tightly screened enclosures or treated with insecticides such as malathion or Sevin.
Pets should be kept indoors during the day and allowed to freely roam at night.
“The black fly is not active during darkness, so letting them out at night is safe,” Robinson explained.
Persons working outdoors or enjoying recreational activities such as boating should wear heavy, long sleeved clothing and use insect repellents.
“Pay close attention to protecting your neck and face with the repellent,” Robinson said.
The infestation could last as late as the end of May, depending on the weather.
Several species of black flies have become more troublesome the last two decades, according to Robinson. The entomologist believes the fly population will continue to build because East Texas watersheds are becoming less polluted. Strict federal and state laws limit applications and ban the use of some types of chemicals entirely. Newer products, though they may not be as innocuous as Bti’s, bio-degrade quicker than older materials.
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