Pyrethroid-Synergist Mixtures: Toxicity˜ Resistance˜and Field Efficacy Toward Pyrethroid-Resistant Horn Flies (Diopters: Muscular)

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Permethrin and cyhalothrin in combination with piper only but oxide (PB), DEF (S,S,S-tributyl phosphorotrithiolate), pirimiphos-ethyl and -methyl were evaluated in the laboratory and the field for activity against pyrethroid-resistant and susceptible horn flies, Haematobia irritants (L.). Horn fly adults from the pyrethroid-resistant population were resistant to permethrin (12.5-fold) but displayed a lower level of resistance to cyhalothrin and cyhalothrin-K (5.4- and 1.7-fold, respectively). Combinations of permethrin plus PB or DEF or both produced a low level of synergism (1.4 to 4.6-fold) but did not reduce the level of resistance present in the pyrethroid-resistant horn flies. The levels of synergism (2.0- to 6.6-fold) observed for combinations of PB, DEF, and PB + DEF with cyhalothrin were marginally higher than for permethrin. Unlike permethrin, the combination of cyhalothrin + PB + DEF resulted in a decreased level of resistance. Pirimiphos-ethyl and -methyl were highly toxic to the horn fly, with virtually no cross-resistance in the pyrethroid-resistant population. Mixtures of pirimiphos-ethyl plus either permethrin or cyhalothrin were highly effective against the resistant horn fly population, but no more so than pirimiphos-ethyl alone. Field studies in 1985 demonstrated that, although the combination of permethrin + PB + DEF was more effective than permethrin alone, control was still inadequate. In these same studies, cyhalothrin provided marginal control while cyhalothrin + PB + DEF produced good results. In 1986, the use of cyhalothrin-K and pirimiphos-methyl resulted in excellent control of the horn fly throughout the season, as did a higher concentration of cyhalothrin and cyhalothrin + pirimiphos-methyl.

Document Type: Research Article

Publication date: December 1, 1988

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  • Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.
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