title: Resistance to synthetic pyrethroid pour-on insecticides in strains of the sheep body louse Bovicola (Damalinia) ovis.
abstract: Groups of sheep infested with strains of Bovicola (Damalinia) ovis were obtained from flocks either with a history of failure to control lice with synthetic pyrethroid (SP) pour-on insecticides, or from farms where SP compounds were not used. The sheep were treated according to the manufacturer's recommendations with registered "off-shears" SP formulations. All treatments were applied under ideal conditions with doses calculated on an individual body weight basis and applied to the dorsal mid-line from the base of the neck to the butt of the tail. Treated sheep were kept in pens and maintained in separate groups. The pour-on SP treatments significantly reduced the lice population but failed to eliminate the infestation in 7 of 13 experiments in sheep carrying strains of lice with resistance factors of greater than 4 to at least one of the SP compounds. Failures occurred with all three of the SP pour-ons currently registered for lice control in NSW and with both water-based and organic solvent-based formulations.
authors.affiliation: NSW Agriculture, Elizabeth Macarthur Agricultural Institute, Camden, New South Wales.
authors.forename: P W
authors.initials: PW
authors.lastname: Johnson
authors.forename: J C
authors.initials: JC
authors.lastname: Boray
authors.forename: K L
authors.initials: KL
authors.lastname: Dawson
mesh_terms: D000287:Administration, Topical; D000818:Animals; D004338:Drug Combinations; D007305:Insecticide Resistance; D007306:Insecticides / Q000008:administration & dosage / Q000627:therapeutic use; D010373:Lice Infestations / Q000188:drug therapy / Q000662:veterinary*; D009570:Nitriles; D008003:Phthiraptera / Q000145:classification; D011722:Pyrethrins / Q000008:administration & dosage / Q000627:therapeutic use; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy*
chemical_list: D004338:Drug Combinations; D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C017160:cypermethrin; C017180:decamethrin