Effects of Treatment Technique on Response of Horn Flies (Diptera: Muscidae) to Permethrin at Different Temperatures1

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Abstract
The toxicity of permethrin to horn flies, Haematobia irritans (L.), was determined at 21, 27, and 32°C. Two populations were tested by the treated-cloth technique: a positive temperature coefficient was observed for both populations between 21 and 27°C, whereas temperature had no significant effect on toxicity between 27 and 32°C. When one of the populations was tested by topical application, however, negative temperature coefficients were observed between pairs of successively higher temperatures. Since the treated-cloth technique simulates exposure to insecticide in the field and topical application does not, our results suggest that, at higher temperatures, permethrin will be more toxic to horn flies.