Evaluation of chlorfenapyr ear tag efficacy and susceptibility of horn flies to chlorfenapyr

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During 1996 and 1997, the efficacy of experimental chlorfenapyr ear tags for 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 ≥90% control for 11, 10, and 16 weeks, respectively. In 1997, fly reduction of ≥90% was observed for chlorfenapyr tags after two weeks post-treatment, and was maintained until week 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 weeks in 1997. The susceptibility of flies to chlorfenapyr, diazinon, and lambda-cyhalothrin was measured at seven locations in LA. All seven horn fly field populations were more susceptible to chlorfenapyr than was a reference susceptible strain. Both pyrethroid- and organophosphate-resistant flies were highly susceptible to chlorfenapyr, with resistance ratios ranging from 0.07 to 0.21.

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Southwestern Entomologist

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