Molecular characterisation of nicotinic acetylcholine receptor subunits from the cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae)

As part of a program to monitor the susceptibility of cat flea populations to the insecticide imidacloprid we have examined the cat flea nicotinic acetylcholine receptor, the target site protein of the neonicotinoid group of insecticides. Seven nAChR subunits (six α-type and one β-type) were identified in cat flea using a degenerate PCR-based strategy. Five of these were expressed in vitro by creating chimeras containing the N-terminal ligand-binding domain of the cat flea subunits and the C-terminal region of the Drosophila Dα2 (SAD) subunit. Two of the five chimeric subunits, Cfα1/Dα2 and Cfα3/Dα2, when co-expressed with rat β2 in Drosophila   S2 cells, showed high-affinity binding of both epibatidine (Kd=1.6±0.6Kd=1.6±0.6 and 0.13±0.06 nM, respectively), and imidacloprid (Ki=142±34Ki=142±34 and 28.7±2.4 nM, respectively). It is likely therefore that Cfα1 and Cfα3 contribute to nAChR populations in vivo that are sensitive to imidacloprid. The identification of cat flea nAChR subunits that have a high affinity for imidacloprid presents candidate genes in which to look for resistance-associated mutations if target-site resistance to imidacloprid arises in domestic pet flea populations.