Willis Bruce—not to be confused with actor Bruce Willis—spent his career studying horn flies. Bruce was an USDA entomologist and professor at the University of Illinois who designed an ingenious walk-through horn fly trap in the 1930s and worked to develop other control methods for these pesky little insects.
Dr. Bruce was particularly interested in the horn fly because it is one of the most widespread and costly external cattle parasites. Current estimates are that horn flies cost the American cattle industry some $2 million every day. Adult flies bite the animal, causing irritation and often drawing blood. As calves spend less time grazing, weight gains will be reduced by an average of 20 pounds per year. But losses may also go much higher:
- Cows produce less milk and may fall out of breeding condition.
- Horn flies have been implicated in the spread of summer mastitis, which tends to be highest in fly season.
- Eye problems may result.
Horn flies are small—adults are about 3⁄16 inch, half the length of a house fly. They are dark gray, blood-sucking flies that stay on cattle almost continuously.
Both male and female horn flies are blood feeders that spend most of their time on the shoulders and backs of cattle. During extremely hot weather or when it rains, they may move to the more protected underside of the animal. They are not strong fliers. When disturbed, horn flies will swarm but return to animals almost immediately. Females leave occasionally to lay eggs in fresh manure piles. If horn flies are not on manure, they are on the animal.
The close association between horn flies and host helps with control. The flies leave animals only to lay eggs or to change hosts, so many methods will expose flies to control practices such as ear tags, topical products, feed-through additives, etc. With some chemistries, insect resistance has been an issue. If a producer applies fly tags, and two weeks later there has been no decline in fly population, the insects are likely resistant to the product.
Resistance is not a problem when using the insect growth regulator (IGR) s-methoprene, brand name Altosid. It has been very effective in controlling biting adult insects that have specific larval environmental requirements, including horn flies and mosquitoes.
When using an IGR feed-through product, horn fly control is long-term and preventive, not reactive. The IGR is ingested as part of the animal’s feed. Cattle then excrete manure that contains the IGR. Horn flies must lay their eggs in fresh manure, and the IGR keeps the horn fly pupae from developing into breeding, biting adult horn flies.
New this spring, MFA has two additional options for fly control in our Gold Star Mineral lineup. Ricochet and Ricochet FESQ Max are now available with Altosid IGR, providing all the features and benefits of these trusted mineral products along with feed-through horn fly control. Given expected intakes, the 0.01 percent level of s-methoprene is adequate for nearly all cattle.
Both are convenient, ready-to-use minerals formulated to balance year-long pasture feeding programs for beef cattle, and they do not require a Veterinary Feed Directive.
Begin to use MFA Gold Star fly control minerals in the spring before horn flies appear on cattle. Flies emerge when 14-day mean temperatures are 65 degrees and above. Continue feeding until cold weather stops fly activity. Make sure to feed IGR mineral throughout the season for a successful fly control program next year. If IGR feeding ends too early, there is a late-season increase in the adult population to lay eggs. The eggs over-winter and are ready to establish fly populations next spring. All that can be avoided by extending the feeding period of fly control minerals for 30 days after a killing frost to minimize the adult population and keep egg populations as low as possible.
Horn fly control with feed-through IGR is the easiest, most effective and economical way of controlling horn flies for cattle producers. To achieve optimum fly control, MFA Ricochet products with Altosid should be used in conjunction with other good management and sanitation practices. A number of integrated pest management resources are available online.