Beef producers who graze cattle in pastures can take several proactive steps to control face flies, which are economically important because they can transmit several eye diseases and parasites to cattle.
Estimates are that $150 million is lost each year to pinkeye treatments, reduced weight gains and reduced milk production from face fly feeding and irritation, says entomologist David Boxler of University of Nebraska–Lincoln Extension.
Closely resembling house flies, the face fly is a robust critter that torments cattle in pasture settings—unlike the stable fly, which inflicts misery on cattle in feedlots.
Adult female face flies typically cluster around the host animal’s eyes, mouth and muzzle, causing extreme annoyance, Boxler says.
The females gather around wounds caused by mechanical damage or biting fly activity to feed on blood and other exudates that are frequently found on the head and face.
By contrast, the male face flies feed only on nectar and dung and are most often seen resting on branches and fences, where they attempt to catch females and mate, notes Boxler.
Female face flies lay eggs only in newly deposited manure from cattle on rangeland or pasture. They do not lay eggs in manure found near barns or stables, or in manure associated with feedlots and dairies since the manure from these locations are often urine-saturated, disturbed or compacted.
When flies emerge, they mate—and then the females seek a protein source, which is necessary for egg development. Typically this source will be secretions from cattle and other animals. Both female and male face flies are strong flyers and can travel several miles to find a host and food source.
Face flies are able to transmit eye diseases and parasites to cattle because of the structure of the fly’s mouth, which has small stomatal teeth used in a rasping manner when feeding. This action scratches the eye or other tissues and creates sites for disease and parasite entry and development.
Female face flies can be contaminated with and transmit infectious bovine keratoconjunctivitis (pinkeye) and infectious bovine rhinotracheitis (IBR). They are also the source of nematode eye worm (Thelazia sp.) infections in cattle and horses.
The female face fly’s persistent feeding habits produce significant annoyance and irritation. Livestock react by bunching, seeking the shade of trees or, in some cases, standing in water to avoid the flies. The cattle’s defensive behavior can also affect grazing patterns.
Providing adequate face fly control can be difficult due to where the female fly feeds on the animal and because the fly is not on the animal most of the time. However, effective control can still be achieved with treatments such as dust bags, oilers and insecticide-impregnated ear tags, Boxler says.
Whole-animal sprays can provide temporary relief, but need to be reapplied regularly (typically every 10–14 days).
Certain feed additives containing insecticides incorporated in a mineral block or added to feed can reduce fly populations. Feed-through products reduce fly larval development in the manure, but have no direct effect on adult face flies—and immigration of flies from neighboring herds can overwhelm control efforts.
If face fly populations are high, control may require more than one method of treatment. Remember that treatment of both calves and cows is necessary for effective control.
To read Boxler’s paper in full, go to http://extensionpublications.unl.edu/assets/pdf/g1204.pdf