title: Determining a diagnostic dose for imidacloprid susceptibility testing of field-collected isolates of cat fleas (Siphonaptera: Pulicidae).
abstract: The susceptibility of four laboratory strains of cat fleas, Ctenocephalides felis (Bouche), to imidacloprid was determined by three different laboratories, by using a standardized bioassay protocol. The probit lines generated by the different laboratories were very similar, with LC50 values ranging from 0.32 to 0.81 ppm. Based on these data, a diagnostic dose (DD) of 3 ppm imidacloprid in larval rearing media was provisionally identified for detecting shifts in tolerance, possibly as a consequence of incipient imidacloprid resistance. None of the larvae from the susceptible laboratory strains survived the DD. Eighteen field-collected isolates were evaluated for their susceptibility to imidacloprid and to validate a DD of 3 ppm. Probit lines from 18 field-collected isolates were very similar, with LC50 values ranging from 0.14 to 1.52 ppm. When exposed to the DD, between 3 and 10% of the exposed larvae emerged as adults from only three of the 18 isolates. All other field isolates gave 100% mortality at the DD. Under the criteria established (>5% survivorship at 3 ppm), two isolates would be established on mammalian hosts and more extensive tests conducted to exclude or confirm the presence of resistance. The DD of 3 ppm is robust enough to eliminate most of the susceptible isolates collected until today, yet low enough to identify possible isolates for further testing.
authors.affiliation: Department of Entomology, University of California, Riverside, Riverside, CA 92521-0314, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Rust
authors.forename: I
authors.initials: I
authors.lastname: Denholm
authors.forename: M W
authors.initials: MW
authors.lastname: Dryden
authors.forename: P
authors.initials: P
authors.lastname: Payne
authors.forename: B L
authors.initials: BL
authors.lastname: Blagburn
authors.forename: D E
authors.initials: DE
authors.lastname: Jacobs
authors.forename: N
authors.initials: N
authors.lastname: Mencke
authors.forename: I
authors.initials: I
authors.lastname: Schroeder
authors.forename: M
authors.initials: M
authors.lastname: Vaughn
authors.forename: H
authors.initials: H
authors.lastname: Mehlhorn
authors.forename: N C
authors.initials: NC
authors.lastname: Hinkle
authors.forename: M
authors.initials: M
authors.lastname: Williamson
mesh_terms: D000818:Animals; D002415:Cats; D004305:Dose-Response Relationship, Drug; D007093:Imidazoles / Q000008:administration & dosage*; D007305:Insecticide Resistance; D007306:Insecticides / Q000008:administration & dosage*; D007814:Larva; D000073943:Neonicotinoids; D009574:Nitro Compounds; D005423:Siphonaptera
chemical_list: D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; C082359:imidacloprid