Zhang_2015_J.Neurochem_135_686

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 Nlalpha8. 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 Nlalpha8 was observed during selection. RNA interference knockdown of Nlalpha8 decreased the sensitivity of N. lugens to imidacloprid, demonstrating that a decrease in Nlalpha8 expression is sufficient to confer resistance in vivo. 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 Nlalpha8 cRNA injected into Xenopus oocytes significantly decreased imidacloprid potency on recombinant receptors. Taken together, these results provide strong evidence that a decrease in Nlalpha8 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. In insects, target-site mutations often cause high resistance to insecticides, such as neonicotinoids acting on nicotinic acetylcholine receptors (nAChRs). Here we found that a quantitative change in target-protein level, decrease in mRNA and protein levels of Nlalpha8, contributed importantly to imidacloprid resistance in Nilaparvata lugens. This finding provides a new target-site mechanism of insecticide resistance.