Progress of the international work of the “imidacloprid flea susceptibility monitoring team”

Abstract

The “Imidacloprid Flea Susceptibility Monitoring Team” has aim to develop and validate a bioassay to effectively monitor and document susceptibility of cat flea (Ctenocephalides felis) isolates to imidacloprid. A larval bioassay was developed, standardized and validated and agreed upon by the team as the reference diagnostic test kit as research has shown that the proposed WHO adult test was not reliable. The selected 3 ppm discriminating dose, determined from evaluating year 2000 field isolates, was approximately 2 times the highest LC₉₅ of the control laboratory flea strains. In 2001 and 2002, this standardized bioassay was used to test more than 190 separate egg collections from individual flea isolates from USA, UK and Germany. If survivorship in the 3 ppm assay is confirmed, the LD₅₀ values of this isolate and the laboratory strains will be determined by a dose-response study in the range of 0.005 to 3 ppm imidacloprid. By comparison of these LD₅₀ values it can be estimated whether a shift in susceptibility to imidacloprid has occurred. In either case the flea isolate will be researched extensively. Currently an in-vivo test which will evaluate the on-host efficacy of Advantage® is being established. None of the to date tested isolates revealed reduced susceptibility to imidacloprid.