Abstract: Honeybees are the main pollinators in the nature. Currently neonicotinoid insecticides are widely used in the control of field pests in China due to its ability of binding to nicotinic acetylcholine receptors (nAChR) and inducing pest death. Imidacloprid, a type of neonicotinoid insecticides, was used in this study to observe the distribution of nAChR-α7 in mushroom body and optic lobes in the brain of adult honeybee (Apis mellifera ligustica) with the immunohistochemical staining method. The results showed that nAChR-α7 was detected in the mushroom bodies and optic lobes of normal adult honeybees, with a stronger labeling in optic lobes. The feeding of sublethal doses of imidacloprid induced down-regulation of nAChR-α7 in the optic lobes but not in the mushroom bodies. The results indicate that in addition to the wellknown inhibition of nAChR, the neonicotinoid insecticide imidacloprid can also suppress the expression of nAChR-α7. This finding might present a novel toxic mechanism of neonicotinoid insecticides in killing pests.

Key words: Apis mellifera ligustica, imidacloprid, nicotine acetylcholine receptor, brain tissue, immunohistochemical staining