Horn Flies: The Billion Dollar Pest

Information courtesy of University of Nebraska

Horn flies are commonly found on the bellies of cattle and can lead to mastitis in cows and heifers even before they calve.

Horn flies are small in size, approximately 3/16” in length and are usually found on the backs, sides and poll area of cattle. During a warm summer afternoon they can be found on the belly region of cattle. Horn flies, both male and females flies, acquire more than 30 blood meals per day

After mating the female fly will leave the animal to deposit eggs in fresh cattle manure. Eggs hatch within one week, and larvae feed and mature in the manure, pupating in the soil beneath the manure pat. Newly emerged horn flies can travel several miles searching for a host. The entire life cycle can be completed in 10 to 20 days depending upon the weather.

Economic losses

Economic losses associated with horn flies are estimated at more than $1 billion dollars annually in the  United States. Horn fly feeding causes irritation, blood loss, decreased grazing efficacy, reduced weight gains, and diminished milk production in mother cows. Additionally, horn flies have been implicated in the spread of summer mastitis.

Studies conducted in the U.S. and Canada have shown that horn flies can cause weight gain loss in cattle, and calf weaning weights can be negatively impacted from 4–15 percent. Studies conducted in Nebraska have established calf weaning weights were 10-20 pounds higher when horn flies were controlled on mother cows. The economic injury level (EIL) for horn flies is 200 flies per animal. Yearling cattle can also be affected by the horn fly; other studies have shown yearling weights can be reduced by as much as 18 percent.

Control methods

There are many insecticide control methods available to manage horn fly numbers; backrubbers, dust bags, insecticidal ear tags and strips, pour-ons, oral larvicides, low pressure sprayers and mist blower sprayers.

Many of these methods require gathering cattle on a regular basis or replenish the various systems that dispense products. A less labor intensive approach is using an insect grown regulator (IGR) in feed or minerals for horn fly control.

When consumed, the insecticide passes through the animal’s digestive system into the manure and prevents larval fly development. For IGRs to be most effective, Central Life Sciences recommends a “30/30 approach.”

1. Begin feeding the IGR approximately 30 days before the average daily daytime temperatures reach 65°F. This is when overwintering flies emerge.

2. Continue feeding the IGR through the fall, 30 days after the first frost has been recorded. This is to help reduce overwintering pupae, giving you a jump start on the next fly season.

3. Monitor fly populations, and supplement your efforts with a horn fly insecticide if needed. Producers who start later in the  season may need to incorporate a knock down spray to kill adults that are already present. To effectively break the horn fly life cycle, a feedthrough program with an IGR like Altosid IGR requires three to four weeks for significant reduction in adult horn flies.

Backrubbers and dust bags are an effective way to reduce horn fly numbers if cattle are forced to use them and they are refilled.

Animal sprays and pour-on products will provide 7-21 days of control and will need to be re-applied throughout the fly season.

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