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STATE DEPARTMENT OF AGRICULTURE BITES BACK AT PESKY BLACK FLIES
Is there such a thing as a fly-free picnic or camping trip? Probably not, but the West Virginia Department of Agriculture (WVDA) continues its black fly control program in an effort to prevent the biting flies from keeping us all indoors.
The insect is about an eighth of an inch long or less and relatively nondescript. Black flies are typically found in large swarms, though, and the female of the species feeds on blood. That combination results in one big pest.
Black fly larvae develop in the fast-moving, well-aerated portions of streams and rivers. Their rate of development depends on water temperature, so efforts to control them must increase as the temperature climbs to match the pace of the insect’s short life cycles.
If control efforts were 100 percent effective, there would be no need for additional applications after the initial ones in early spring. But some larvae don’t eat the bacterial pesticide, and it doesn’t take many to keep the population cycling. Applications begin in March and typically continue until early October.
Treatments are conducted on the New River from near the West Virginia/Virginia border to Sandstone. The Greenbrier River is treated from Anthony to its confluence with the New River. The lower 13 miles of the Bluestone River are also treated. Spraying is never done on holidays, and weekends are also avoided.
Some people are understandably concerned about the safety to humans of the product used to suppress black-fly populations. Others worry that it reduces fish numbers by reducing their food supply, while some wonder what fewer flies mean for songbirds.
The product, seen sprayed from helicopters onto the waters of the New, Greenbrier and Bluestone Rivers, goes by the trade name “VectoBac.” It is a solution of bacteria, namely Bti (Bacillus thuringiensis israelensis), that occurs naturally in soil.
When eaten by the larvae of black flies and mosquitoes, the high (alkaline) pH of their guts causes a toxin to be released that ruptures their digestive tract, resulting in death. Alive or dead, the larvae are available as non-toxic fish food. Without doubt, Bti is eaten by other aquatic organisms, but the acidity of their guts prevents harm.
To make sure Bti is as host-specific as the FDA and its manufacturers claim, WVDA personnel check the rivers a few days after each application of Bti. Robust populations of snails, riffle beetles, flatworms, and various larvae (mayflies, stoneflies, caddisflies, damselflies, etc.) are observed and are apparently unaffected by Bti. However, black fly numbers plummet, as do complaints about bites from the adult flies. Mosquito larvae are not affected, as they occur in stagnant waters, such as ponds, which are not targeted.
The helicopter pilots who apply the Bti are careful to avoid anglers, boaters and swimmers, but aren’t always able to see people in time to avoid them. Once in a while someone is unintentionally sprayed.
Although it has a fishy odor, the spray carries no chemical pesticide and is non-toxic to mammals. The inert ingredients in VectoBac can cause mild irritation to eyes or skin, so the manufacturer recommends a 20-minute shower if exposed.
Research by the National Park Service has not been able to detect effects of the spray program on fish or aquatic invertebrate populations. In addition, the West Virginia Division of Natural Resources website reports good fishing for smallmouth bass in the Greenbrier and New Rivers this year, as well as the state record for striped bass (37.75 pounds!) caught in Bluestone Lake last year.
Songbirds are not known to be adversely affected by the spray program. Even though black fly populations drop, birds readily turn to other sources of food if one is in short supply.
For more information, contact Betsy Reeder, Coordinator of WVDA’s Black Fly Control Program at breeder@ag.state.wv.us or 304-541-5471.
The West Virginia Department of Agriculture protects plant, animal and human health through a variety of scientific, regulatory and consumer protection programs, as mandated by state law. The Commissioner of Agriculture is one of six statewide elected officials in West Virginia. Currently, Commissioner Gus R. Douglass is the longest-serving agriculture commissioner in the nation. For more information, visit www.wvagriculture.org.
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