differences between horn fly densities on cattle pastured in Wyoming and Nebraska as possibly influenced by elevation

Adult horn fly densities were determined at three elevations (800, 1800 and 2400 m) over two years using fly counts on cattle. In 1995, cattle at the 800 m elevation had the highest density of flies. In 1996, the greatest density of flies occurred on cattle at the 1800 m elevation. In both 1995 and 1996, the fewest flies were recorded on cattle at the 2400 m elevation, with densities below 90 flies per side. Based on published economic injury levels, control of horn flies at elevations above 2400 m may not be economically justifiable in Wyoming. Cattle grazed at elevations at or below 1800 m may not have horn fly populations large enough to merit control and therefore should be examined for fly densities before control measures are taken.