Evaluation of a yearly insecticidal ear tag rotation for control of pyrethroid-resistant horn flies (Diptera : Muscidae)

From 1991 to 1997, the yearly alternated use of synergized pyrethroid (lamb da-cyhalothrin + piperonyl butoxide) and organophosphate (pirimiphos-methyl ) ear tags was evaluated for the control of two pyrethroid-resistant horn f ly populations in Louisiana. At each site, weekly fly counts were used to a ssess product efficacy. Control achieved by synergized pyrethroid ear tag t reatments was reduced from 7 to 2 weeks and from 4 to 0 weeks at St. Joseph and Winnsboro, respectively. Control by organophosphate ear tags decreased from 15 to 3 weeks and from 10 to 7 weeks at St. Joseph and Winnsboro, res pectively. The rotation of synergized lambda-cyhalothrin and pirimiphos-met hyl ear tags did not improve pyrethroid ear tag efficacy or prevent further development of resistance to the pyrethroid or OP compound. (C) 1999 Elsev ier Science B.V. All rights reserved.