The R81T mutation in the nicotinic acetylcholine receptor of Aphis gossypii is associated with neonicotinoid insecticide resistance with differential effects for cyano- and nitro-substituted neonicotinoids

The cotton aphid, Aphis gossypii Glover, is one of the most agriculturally important insect pests. Neonicotinoid insecticides and sulfoxaflor have generally shown excellent control of A. gossypii, but these aphids have recently developed resistance against neonicotinoid insecticides. We previously characterized a field-collected A. gossypii Kushima clone that showed higher resistance to nitro-substituted neonicotinoids, such as imidacloprid, than to cyano-substituted neonicotinoids, such as acetamiprid. This Kushima clone harbors the R81T mutation in the nicotinic acetylcholine receptor (nAChR) β1 subunit; this mutation is the source of neonicotinoid insecticide resistance. In the present study, electrophysiological analyses and molecular modeling were employed to investigate the differential effects of the R81T mutation on cyano- and nitro-substituted neonicotinoids and sulfoxaflor. We isolated full-length coding sequences of A. gossypii nAChR α1, α2, and β1 subunits. When co-expressed in Xenopus laevis oocytes with chicken β2 nAChR, A. gossypii α1 evoked inward currents in a concentration-dependent manner in response to acetylcholine (ACh) and showed sensitivity to neonicotinoid and sulfoxaflor. Additionally, the chicken β2 T77R+E79V (equivalent double mutant of R81T) mutation resulted in a lower effect to cyano-substituted neonicotinoids and sulfoxaflor than to nitro-substituted neonicotinoids. Electrophysiological data and nAChR homology modeling analysis suggested that the Kushima clone exhibited different levels of resistance to cyano- and nitro-substituted neonicotinoid insecticides.

Molecular modeling of sulfoxaflor and neonicotinoid binding in insect nicotinic acetylcholine receptors: impact of the Myzus β1 R81T mutation

BACKGROUND

Sulfoxaflor (Isoclast™ active), a new sulfoximine-class insecticide, targets sap-feeding insect pests, including those resistant to neonicotinoids. Sulfoxaflor acts on the insect nicotinic acetylcholine receptor (nAChR) in a distinct manner relative to neonicotinoids. Unlike any of the neonicotinoids, sulfoxaflor has four stereoisomers. A homology model of Myzus persicae (green peach aphid) based on the ACh binding protein from Aplysia californica, overlaid with M. persicae nAChR sequence (α2 and β1 subunits) was used to investigate the interactions of the sulfoxaflor stereoisomers with WT and R81T versions of the nAChR.

RESULTS

Whole-molecule van der Waals interactions are highly correlated with the binding affinity for the neonicotinoids and correctly predict the rank order of binding affinity for neonicotinoids and sulfoxaflor. The R81T mutation in M. persicae nAChR is predicted to have much less effect on binding of sulfoxaflor's stereoisomers than that of the neonicotinoids.

CONCLUSION

All four stereoisomers predictably contribute to the activity of sulfoxaflor. The WT and R81T nAChR homology models suggest that changes in a whole-molecule electrostatic energy component can potentially explain the effects of this target-site mutation on the pattern of reduced efficacy for the modeled neonicotinoids, and provide a basis for the reduced effect of this mutation on sulfoxaflor. © 2016 Society of Chemical Industry.