title: Evidence for occurrence of an organophosphate-resistant type of acetylcholinesterase in strains of sea lice (Lepeophtheirus salmonis Krøyer).
abstract: Acetylcholinesterase (AChE) is the target of a major pesticide family, the organophosphates, which were extensively used as control agents of sea lice on farmed salmonids in the early 1990s. From the mid-1990s the organophosphates dichlorvos and azamethiphos were seriously compromised by the development of resistance. AChE insensitive to organophosphate chemotherapeutants has been identified as a major resistance mechanism in numerous arthropod species, and in this study, target-site resistance was confirmed in the crustacean Lepeophtheirus salmonis Krøyer isolated from several fish-farming areas in Norway and Canada. A bimolecular rate assay demonstrated the presence of two AChE enzymes with different sensitivities towards azamethiphos, one that was rapidly inactivated and one that was very slowly inactivated. To our knowledge this is the first report of target-site resistance towards organophosphates in a third class of arthropods, the Crustacea.
authors.affiliation: The Norwegian School of Veterinary Science, PO Box 8146 Dep, N-0033 Oslo, Norway. anders.fallang@veths.no
authors.forename: Anders
authors.initials: A
authors.lastname: Fallang
authors.forename: Jennifer Mara
authors.initials: JM
authors.lastname: Ramsay
authors.forename: Sigmund
authors.initials: S
authors.lastname: Sevatdal
authors.forename: John F
authors.initials: JF
authors.lastname: Burka
authors.forename: Philip
authors.initials: P
authors.lastname: Jewess
authors.forename: K Larry
authors.initials: KL
authors.lastname: Hammell
authors.forename: Tor E
authors.initials: TE
authors.lastname: Horsberg
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism*; D000818:Animals; D017756:Aquaculture; D002170:Canada; D033342:Copepoda / Q000187:drug effects* / Q000201:enzymology; D004478:Ectoparasitic Infestations / Q000662:veterinary; D005260:Female; D005393:Fish Diseases / Q000469:parasitology; D007305:Insecticide Resistance / Q000502:physiology; D009664:Norway; D063086:Organothiophosphates / Q000494:pharmacology*; D012474:Salmon / Q000469:parasitology
chemical_list: D063086:Organothiophosphates; C072763:azamethiphos; D000110:Acetylcholinesterase