title: High levels of pyrethroid resistance in horn flies (Diptera: Muscidae) selected with cyhalothrin.
abstract: Lambdacyhalothrin cattle ear tags controlled horn fly, Haematobia irritans (L.), for 14 wks or longer during 1986-1988 in Georgia, USA. In 1989 and 1990, control of < 50 horn flies per side of cow was achieved for < or = 4 wk because of high levels of pyrethroid resistance in horn flies selected with lambdacyhalothrin. The highest resistance ratios (RRs) were seen in 1989. These were 498 for lambdacyhalothrin; 92,000 for fenvalerate; and 54 for permethrin. RRs for cypermethrin as high as 8,800 were estimated in 1990 when the RR for fenvalerate was only 1,060. No cross-resistance to diazinon was detected. These high levels of pyrethroid resistance seem to have a large component of metabolic resistance. Synergistic coefficients as high as 3,600 were determined by addition of nonlethal amounts of piperonyl butoxide. Resistance development in a no-pyrethroid-use area indicates movements of > or = 3km by sufficient numbers of horn flies can significantly change the RR.
authors.affiliation: Department of Entomology, University of Georgia, Tifton 31793.
authors.forename: D C
authors.initials: DC
authors.lastname: Sheppard
authors.forename: J A
authors.initials: JA
authors.lastname: Joyce
mesh_terms: D000818:Animals; D007305:Insecticide Resistance; D007306:Insecticides; D009117:Muscidae; D009570:Nitriles; D011722:Pyrethrins
chemical_list: D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C037304:cyhalothrin