Evaluation of chlorfenapyr ear tag efficacy and susceptibility of horn flies Diptera : Muscidae to chlorfenapyr

During 1996 and 1997, the efficacy of experimental chlorfenapyr ear tags fo r horn fly control was evaluated under field conditions at St. Gabriel, LA. In 1996. the 30, 40, and 40% TT (thicker tags) chlorfenapyr tags provided greater than or equal to 90% control for 11, 10, and 16 weeks, respectively . In 1997, fly reduction of greater than or equal to 90% was observed for c hlorfenapyr tags after two weeks post-treatment, and was maintained until w eek 8, 8, and 18 by the 20, 30, and 30% TT tags, respectively. At least 90% control was obtained with 40% diazinon tags for 23 weeks in 1996 and 16 we eks in 1997. The susceptibility of flies to chlorfenapyr, diazinon, and lam bda-cyhalothrin was measured at seven locations in LA. All seven horn fly f ield populations were more susceptible to chlorfenapyr than was a reference susceptible strain. Both pyrethroid- and organophosphate resistant flies w ere highly susceptible to chlorfenapyr, with resistance ratios ranging from 0.07 to 0.21.