Insecticide impregnated ear tags and insecticide resistance management for horn flies (Haematobia irritans) on pastured and range cattle

The horn fly, Haematobia irritans (Linnaeus), is the most economically important ectoparasite of pastured and range cattle in the United States. At the present time cultural and biological control methods offer only limited potential for control of horn flies compared to chemical control methods. Due to the highly dispersed nature of pasture and range cattle, insecticide impregnated ear tags make the ideal method to control this pest. Because horn flies have multiple generations per year and ear tags release their insecticide load in an inverse exponential manner horn flies have a tremendous ability to develop resistance to the insecticides in ear tags. For this reason and the limited potential of alternate strategies in many states, IPM programs for pastured cattle should center on the management of horn fly insecticide resistance. Thirty years ago the first tags to receive wide acceptance contained synthetic pyrethroids. They provided five months control in most regions. Within three years the first evidence of product failure due to resistance started to appear in the southern United States by five years it had spread all across the US. Then organophosphate ear tags were developed and presented the possibility for insecticide rotation. Now there are three classes of insecticides (synthetic pyrethroid, organophosphate, and abamectin) for use in impregnated ear tags that can be used in annual rotation along with alternative control methods.