The complete life cycle, egg to adult, can be completed in 10 to 20 days during hot weather. This rapid life cycle and the number of eggs explains the rapid build-up of fly numbers in the early summer. Horn fly numbers generally reach a peak in early summer and then decline during hot, dry weather because the manure dries before many of the flies complete their larval development. A second peak usually occurs in late August and September as temperatures cool and moisture increases. For a listing of specific insecticides recommended for horn fly control, refer to EC 92-1550, Nebraska Management Guide for Arthropod Pests of Livestock and Horses .
Ear tags contain insecticide in the matrix of the tag.
The first tags contained Rabon dust which provided control for only seven to eight weeks, and the tag was too heavy causing necrosis at the attachment site in the ear. The Rabon tags were replaced with pyrethroid insecticides. However, within two years, horn fly populations started to develop resistance to the pyrethroids and, within another two years, the resistance spread from Florida to Canada. The pyrethroids were highly effective and had long residual. During its use a small percentage of the horn fly population were resistant to pyrethroid insecticides.