The development and use of ear tags containing pesticides in the mid-1
970s led to the control of horn flies throughout most of the United St
ates. In the last decade, however, evidence has shown that horn flies
have developed a high resistance to pyrethroids. This situation repres
ents the first potential loss of a major pesticide group to resistance
in the large animal health area in the United States. Specific treatm
ent options are presented, and ways of increasing producer education a
nd awareness of horn fly resistance and control are discussed.