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1 July 2005 Determining a Diagnostic Dose for Imidacloprid Susceptibility Testing of Field-Collected Isolates of Cat Fleas (Siphonaptera: Pulicidae)
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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.

M. K. Rust, I. Denholm, M. W. Dryden, P. Payne, B. L. Blagburn, D. E. Jacobs, N. Mencke, I. Schroeder, M. Vaughn, H. Mehlhorn, N. C. Hinkle, and M. Williamson "Determining a Diagnostic Dose for Imidacloprid Susceptibility Testing of Field-Collected Isolates of Cat Fleas (Siphonaptera: Pulicidae)," Journal of Medical Entomology 42(4), 631-636, (1 July 2005). https://doi.org/10.1603/0022-2585(2005)042[0631:DADDFI]2.0.CO;2
Received: 26 October 2004; Accepted: 1 March 2005; Published: 1 July 2005
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