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The binding properties of cycloxaprid on insect native nAChRs partially explain the low cross-resistance with imidacloprid in Nilaparvata lugens.

BACKGROUND
Neonicotinoids, such as imidacloprid, are selective agonists of insect nicotinic acetylcholine receptors (nAChRs) used to control Nilaparvata lugens, a major rice insect pest. High imidacloprid resistance has been reported in N. lugens both in the laboratory and in the field. Cycloxaprid (CYC), an oxa-bridged cis-nitromethylene neonicotinoid, showed high insecticidal activity against N. lugens and low cross-resistance in imidacloprid-resistant strains and field populations.


RESULTS
Binding studies demonstrated that imidacloprid has two binding sites with different affinities (Kd = 3.18 ± 0.43 pm and 1.78 ± 0.19 nm) in N. lugens nAChRs. CYC was poor at displacing [3 H]imidacloprid at its high-affinity binding site (Ki = 159.38 ± 20.43 nm), but quite efficient at the low-affinity binding site (Ki = 1.27 ± 0.35 nm). These data showed that CYC had overlapping binding sites with imidacloprid only at its low-affinity binding site. Therefore, the low displacement ability of CYC against imidacloprid binding at its high-affinity site could partially explain the low cross-resistance of CYC in imidacloprid-resistant populations.


CONCLUSION
The high insecticidal activity, low cross-resistance and different binding properties on insect nAChRs of CYC show that it is a potential insecticide for the control of N. lugens and related insect pests, especially ones with high resistance to neonicotinoids. © 2018 Society of Chemical Industry.