Whitefly (Hemiptera: Aleyrodidae) Binding Site for lmidacloprid and Related Insecticides: A Putative Nicotinic Acetylcholine Receptor

Imidacloprid is used extensively to control sweetpotato whiteflies, Bemisia argentifolii Bellows & Perring [also known as B. tabaci (Gennadius) biotype B]. As a radioligand, [3H]imidacloprid binds rapidly to a single class of high-affinity sites in membrane preparations from whole adult whiteflies with an apparent dissociation constant of 2 nM and maximal binding capacity of 101 fmol/mg protein. Three related compounds (the nitromethylene analog of imidacloprid, acetamiprid, and nitenpyram) inhibit [3H]imidacloprid binding by 50% at 0.40, 2.9, and 57 nM, respectively. The pharmacological profile of the binding site (examined with imidacloprid and the analogs listed above, and nicotine, alpha-bungarotoxin, carbachol, acetylcholine [with paraoxon], and atropine) is consistent with that anticipated for a nicotinic acetylcholine receptor and correlates well with binding results for house fly, Musca domestica L., head membranes under the same conditions. Thus, [3H]imidacloprid is a suitable radioligand to investigate the putative nicotinic acetylcholine receptor of Bemisia and the possible modifications of this target site associated with selection of resistant strains.