A nicotinic acetylcholine receptor transmembrane point mutation (G275E) associated with resistance to spinosad in Frankliniella occidentalis

Abstract

High levels of resistance to spinosad, a macrocyclic lactone insecticide, have been reported previously in western flower thrips, Frankliniella occidentalis, an economically important insect pest of vegetables, fruit and ornamental crops. We have cloned the nicotinic acetylcholine receptor (nAChR) α6 subunit from F. occidentalis (Foα6) and compared the nucleotide sequence of Foα6 from susceptible and spinosad-resistant insect populations (MLFOM and R1S respectively). A single nucleotide change has been identified in Foα6, resulting in the replacement of a glycine (G) residue in susceptible insects with a glutamic acid (E) in resistant insects. The resistance-associated mutation (G275E) is predicted to lie at the top of the third α-helical transmembrane domain of Foα6. Although there is no direct evidence identifying the location of the spinosad binding site, the analogous amino acid in the C. elegans glutamate-gated chloride channel lies in close proximity (4.4 Å) to the known binding site of ivermectin, another macrocyclic lactone pesticide. The functional consequences of the resistance-associated mutation have been examined in the human nAChR α7 subunit. Introduction of an analogous (A272E) mutation in α7 abolishes the modulatory effects of spinosad whilst having no significant effect upon activation by acetylcholine, consistent with spinosad having an allosteric mechanism of action.

Allosteric modulation of nicotinic acetylcholine receptors

“…Spinosad, like ivermectin, is a macrocyclic lactone pesticide that acts as an allosteric modulator of nAChRs [157]. Recent studies of spinosad-resistant insects have identified a resistance-associated point mutation in the nAChR transmembrane domain that is consistent with spinosad binding to nAChRs in a similar inter-subunit transmembrane site to the known binding site of ivermectin in GluCl [158].…”

The invertebrate pharmacology of insecticides acting at nicotinic acetylcholine receptors

“…149) Spinosynresistance in western flower thrips Frankliniella occidentalis has been identified to a point mutation G275E located at the third α-helical TMD of Foα6. 150) Laboratory selection of the oriental fruit fly Bactrocera dorsalis generated high-level spinosyn resistance also associated with non-functional α6 subunits due to truncated transcripts. 151) Given these observations it has been suggested that any mutation that causes a loss of α6 will confer resistance to spinosad.…”

Benzoylurea resistance in western flower thrips <i>Frankliniella occidentalis</i> (Thysanoptera: Thripidae): the presence of a point mutation in <i>chitin synthase 1</i>

“…1) For example, cytochrome P450 monooxygenases are reported to be involved in resistance against organophosphates, 2,3) carbamates, 2,4) pyrethroids, 2,3) and neonicotinoids 5) in F. occidentalis [reviewed in 1,6) ]. In addition, point mutations at target sites have been reported: for example, a nonsynonymous substitution in the nicotinic acetylcholine receptor (nAChR) has been identified in spinosad-resistant strains of F. occidentalis 7) and in the melon thrips, Thrips palmi. 8) Thus, both metabolic detoxification and target site mutation are involved in insecticide resistance in thrips, as reported in other insect species.…”