Determining a Diagnostic Dose for Imidacloprid Susceptibility Testing of Field-Collected Isolates of Cat Fleas (Siphonaptera: Pulicidae)

Authors: Rust, M. K.; Denholm, I.; Dryden, M. W.; Payne, P.; Blagburn, B. L.; Jacobs, D. E.; Mencke, N.; Schroeder, I.; Vaughn, M.; Mehlhorn, H.; Hinkle, N. C.; Williamson, M.

Source: Journal of Medical Entomology, Volume 42, Number 4, July 2005 , pp. 631-636(6)

Abstract:

The susceptibility of four laboratory strains of cat fleas, Ctenocephalides felis (Bouché), 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.

Keywords: cat fleas; Ctenocephalides felis; insecticide resistance; monitoring; imidacloprid

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