INFLUENCE OF INSECTICIDE MIXTURES IMPREGNATED IN CATTLE EAR TAGS FOR MANAGEMENT OF PYRETHROID-RESISTANT HORN FLIES (DIPTERA, MUSCIDAE)

Ear tags impregnated with a mixture of cyhalothrin-piperonyl butoxide-DEF (S,S,S,-tributyl phosphorotrithiolate) or cypermethrin-piperonyl butoxide-chlorpyrifos were evaluated for the management of pyrethroid-resistant horn flies, Haematobia irritans (L.), on cattle in Kentucky. At the time of treatment, all horn fly populations were resistant to the pyrethroids in these mixtures. Although acceptable control of horn flies (average > 92%) was generally achieved on treated animals, LC50s for the pyrethroid mixture tested on each population were 2-33 times greater after 14 wk exposure compared with values before treatment. At the end of this exposure period, the frequency of pyrethroid-resistant individuals remaining in each of the treated horn fly populations was 100%.