Reduction in mRNA and protein expression of a nicotinic acetylcholine receptor alpha 8 subunit is associated with resistance to imidacloprid in the brown planthopper, Nilaparvata lugens

Target-site resistance is commonly caused by qualitative changes in insecticide target-receptors and few studies have implicated quantitative changes in insecticide targets in resistance. Here we show that resistance to imidacloprid in a selected strain of Nilaparvata lugens is associated with a reduction in expression levels of the nicotinic acetylcholine receptor (nAChR) subunit Nl8. Synergism bioassays of the selected strain suggested resistance was conferred, in part, by a target-site mechanism. Sequencing of N.lugens nAChR subunit genes identified no mutations associated with resistance, however, a decrease in mRNA and protein levels of Nl8 was observed during selection. RNA interference knockdown of Nl8 decreased the sensitivity of N.lugens to imidacloprid, demonstrating that a decrease in Nl8 expression is sufficient to confer resistance invivo. Radioligand binding assays revealed that the affinity of the high-affinity imidacloprid-binding site of native nAChRs was reduced by selection, and reducing the amount of Nl8 cRNA injected into Xenopus oocytes significantly decreased imidacloprid potency on recombinant receptors. Taken together, these results provide strong evidence that a decrease in Nl8 levels confers resistance to imidacloprid in N.lugens, and thus provides a rare example of target-site resistance associated with a quantitative rather than qualitative change.