Monitoring field susceptibility to imidacloprid in the cat flea: a world-first initiative twelve years on

In 2001, an international surveillance initiative was established, utilising a validated larval development inhibition assay to track the susceptibility of cat flea isolates to imidacloprid. In 2009, an Australian node was incorporated into the programme, joining laboratories in the United States and Europe. Field isolates of Ctenocephalides felis eggs were submitted to participating laboratories and, where egg quantity and quality was sufficient, were placed in the imidacloprid discriminating dose bioassay for evaluation. Between 2002 and 2012, a total of 2,307 cat flea isolates were received across all sites; 1,685 submissions (73 %) were suitable for placement into the bioassay. In the Northern Hemisphere, isolate submission rate was influenced by season, with highest numbers submitted between June and October. In Australia, pets with flea infestations could be sourced year-round, and submission rate was largely influenced by programme factors and not climate. A total of 1,367 valid assays were performed between 2002 and 2012 (assay validity data was not recorded in 2001); adult flea emergence 5 % or greater at 3 ppm imidacloprid was observed in 38 of these assays (2.8 %). For these isolates that reached the threshold for further investigation, re-conduct of the assay using either a repeat challenge dose of 3 ppm of imidacloprid or a dose response probit analysis confirmed their susceptibility to imidacloprid. From 2009 to 2012, the Australian node performed valid assays on 97 field isolates from a total of 136 submissions, with no adult emergence observed at the 3-ppm imidacloprid discriminating dose. In addition to reviewing the data generated by this twelve-year initiative, this paper discusses lessons learned from the coordination and evolution of a complex project across geographically dispersed laboratories on three continents.