Photo by Stephen Ausmus. Filth flies are a pain, especially stable flies that will travel several miles just to bite livestock, pets and people. They often attack the ankles and lower legs, inflicting sharp, stabbing bites.
For cattle producers, these attacks can be costly, resulting in lower milk production in dairy cows, less weight gain in beef cattle, and reduced feed efficiency.
Agricultural Research Service (ARS) scientists are developing improved methods to locate stable fly habitats, finding easier and more efficient ways to control them, and using innovative techniques to stop flies from reproducing.
Staking Out Sites
In the past, stable flies have mainly been associated with stables and barnyards, but over the past three decades, they've become a significant pest in pastures as well and are now the most damaging arthropod pest of U.S. cattle.
Large bales of hay, placed in fields and used as supplemental cattle feed, are partly to blame. Scientists at the ARS Agroecosystem Management Research Unit (AMRU) in Lincoln, Neb., determined that hay-feeding sites are the primary sources of peak fly populations during summer months in the state.
The accumulation of wasted hay, manure and urine at these feeding sites creates an ideal habitat in the pasture for stable fly larval development, says AMRU entomologist David Taylor. For 100 years, the primary method used to control stable flies has been to clean up sites where they dwell. However, infested hay-feeding sites are often in remote locations.
"Producers need to know if the time it takes to clean up a site is worth their time and expense," Taylor says. "We developed a model to assess the economic impact of stable flies and to provide a cost-benefit analysis to producers."
The model was based on four classes of production: dairy; cow/calf; pastured and range stocker; and animals on feed. The analysis showed that stable flies cost the U.S. cattle industry more than $2.4 billion each year.
Preventing Flies from Growing
Insecticides used to control flies at hay-feeding sites usually wear off in two or three days, according to Taylor. An insect growth regulator that prevents stable flies from developing can be more effective.
Taylor and his team used a commercial product called cyromazine to control immature stable flies. The product, which has been used to manage other species of flies, inhibits flies from developing into adults.
In the study, one application of granular cyromazine sprinkled on a hay-feeding site reduced the number of adult stable flies emerging by 97 percent. Treatments took only 10 minutes, cost $10 per site, and remained effective for two to five months.