Neonicotinoid insecticide interact with honeybee odorant-binding protein: Implication for olfactory dysfunction.

The decline of bee population has caused great concern in recent years. A noticeable factor points to the neonicotinoid insecticides, which remain in the nectar and pollen of plants and impair the olfactory cognition of foraging bees. However, it remains elusive that if and how neonicotinoid insecticides interact with the olfactory system of bees. Herein, we studied the binding interaction between neonicotinoid imidacloprid and ASP2, one odorant-binding protein in eastern bees, Apis cerana, by multispectroscopic methods. The results indicate that imidacloprid significantly quenched the intrinsic fluorescence of ASP2 as the static quenching mode, and expanded the conformation of ASP2 measured by the circular dichroism (CD) spectra. The acting force is mainly driven by hydrophobic force based on thermodynamic analysis. Docking analysis predicts a formation of a hydrogen bond, while the corresponding site-directed mutagenesis indicated that the hydrogen bond is not main force here. Moreover, imidacloprid with a sublethal dose (0.8ng/bee) clearly decreased the binding affinity of ASP2 to a floral volatile, β-ionone, which had been identified to strongly bind with the wild ASP2 before. This study may benefit to evaluate the effect of neonicotinoid insecticides on the olfactory cognitive behavior of bees involved in the crops pollination.