title: Unstable pyrethroid resistance in sheep body lice Bovicola ovis (Schrank), (Phthiraptera: Trichodectidae) and its implications for lice control on sheep.
abstract: A retrospective study in which the 18 years treatment history of a mob of sheep hosting a pyrethroid resistant strain of sheep body lice was compared with the coincidental changes in that strain's response to cypermethrin, provided a unique opportunity to investigate the stability of pyrethroid resistance in this species. Resistance levels remained very high (resistance factors (RF)=75-145) for at least five years following the cessation of pyrethroid treatments but within ten years had dropped to only 5, a level similar to many normal field strains and certainly not indicative of high-level resistance. Resumption of pyrethroid treatment of sheep infested with these lice caused a coincidental increase in resistance to an extreme level (RF=321) within two years. Wool producers considering a return to pyrethroid use to control louse infestations should be aware that such a strategy may not be sustainable in the long term and that in Australia effective registered alternative treatments are available.
authors: Elizabeth Macarthur Agricultural Institute, Industry & Investment NSW I Primary Industries, Private Bag 4008, Narellan, NSW 2567, Australia. garry.levot@industry.nsw.gov.au
authors: Garry
authors: G
authors: Levot
mesh_terms: D000818:Animals; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D058326:Ischnocera / Q000187:drug effects*; D009570:Nitriles / Q000494:pharmacology*; D011722:Pyrethrins / Q000494:pharmacology*; D012189:Retrospective Studies; D012756:Sheep; D012757:Sheep Diseases / Q000469:parasitology* / Q000517:prevention & control
chemical_list: D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C017160:cypermethrin; C037304:cyhalothrin