Molecular Characterization and Imidacloprid Selectivity of Nicotinic Acetylcholine Receptor Subunits from the Peach‐Potato Aphid Myzus persicae

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Abstract
The recent introduction of the chloronicotinyl insecticide imidacloprid, targeting insect nicotinic acetylcholine receptors (nAChRs), emphasises the importance of a detailed molecular characterisation of these receptors. We are investigating the molecular diversity of insect nAChR subunit genes in an important agricultural pest, the peach‐potato aphid Myzus persicae. Two M. persicaeα‐subunit cDNAs, Mpα1 and Mpα2, have been cloned previously. Here we report the isolation of three novel α‐subunit genes (Mpα3‐5) with overall amino acid sequence identities between 43 and 76% to characterised insect nAChR subunits. Alignment of their amino acid sequences with other invertebrate and vertebrate nAChR subunits suggests that the insect α subunits evolved in parallel to the vertebrate neuronal nAChRs and that the insect non‐α subunits are clearly different from vertebrate neuronal β and muscle non‐α subunits. The discovery of novel subtypes in M. persicae is a further indicator of the complexity of the insect nAChR gene family. Heterologous co‐expression of M. persicae nAChR α‐subunit cDNAs with the rat β2 in Drosophila S2 cells resulted in high‐affinity binding of nicotinic radioligands. The affinity of recombinant nAChRs for [3H]imidacloprid was influenced strongly by the α subtype. This is the first demonstration that imidacloprid selectively acts on Mpα2 and Mpα3 subunits, but not Mpα1, in M. persicae.