In 1999, three experimental 20% diazinon 20% coumaphos impregnated ear tags and a 40% diazinon ear tag reduced horn fly numbers by 70% at the University of Nebraska Research Ranch near Whitman, Nebraska for 16 weeks. Two other insecticide ear tags, 8% beta cyfluthrin 20% piperonyl butoxide (PBO) and 10% lambdacyfluthrin 13% PBO reduced horn fly numbers by 95% and 86% respectively at a University of Nebraska pasture site near Ithaca, Nebraska for eight weeks. In 2003 some of the same insecticidal ear tags were reevaluated. Ear tags containing 10% zeta-cypermethrin 20% PBO, 20% diazinon 20% coumaphos, 10% lambdacyfluthrin 13% PBO, 8% beta-cyfluthrin 20% PBO and 40% diazinon provided a reduction in horn fly numbers ranging from 81.89% to 88.3% at the University Research Ranch for 12 weeks.