The most damaging insect pest for beef cattle in Texas is the horn fly (Fig. 1). Research shows that a calf infested with more than 200 horn flies will weigh 15 to 50 pounds less at weaning. Horn fly feeding on dairy cows can also reduce milk production up to 20 percent. To suppress horn flies effectively and economically:
- Identify them properly,
- Understand the insect’s life cycle, and
- Use a combination of control strategies.
Identifying horn flies
Figure 1. Horn flies resting on the back of a cow. Photo: Jeff Tomberlin, Texas A&M University Horn flies look like house flies and stable flies but are slightly smaller (Fig. 2). Like the stable fly, horn flies have piercing mouthparts. To distinguish horn flies from stable flies, observe their feeding behavior. Horn flies rest on an animal between feedings; stable flies remain on the animal only while feeding. Also, horn flies feed most often on an animal’s back, shoulders, and sides, whereas stable flies feed principally on the legs.
Horn flies lay eggs in fresh manure pats, where they hatch as maggots. They develop from the egg to the adult stage within 10 to 20 days and live for about 3 weeks, feeding 20 to 30 times a day. In Central Texas, horn flies are usually first observed in early spring. Populations tend to peak in early summer, then decline when the weather becomes hot and dry. In the fall, horn fly populations usually surge again when the temperatures drop and rainfall increases. Generally, they are no longer a problem after October or November, depending on when temperatures start to drop.
Figure 2. Comparison of the horn fly to the stable fly, house fly, and face fly. Photo: Photo: John B. Campbell, University of Nebraska-Lincoln
To suppress horn fly populations efficiently, use an integrated pest management (IPM) approach. IPM relies on multiple tactics including cultural, biological, and chemical methods to suppress insect pests.
Biological control: Parasitic wasps suppress horn fly populations naturally. Producers who want to use parasitic wasps to control horn flies can order fly pupae parasitized with the wasps from insectaries in Texas or across the United States. The parasitized pupae are best used around barns where manure accumulations allow for the development of fly pests. However, research has not proven that releasing parasitic wasps suppresses horn flies or that the use of parasitized pupae reduces them in pasture situations.