Abstract: 【Aim】 Honeybees are important pollinators, but they are endangered by neonicotinoid insecticides like imidacloprid which mainly impair nerve cells of honeybee brain. Our research aimed to explore the apoptosis in the nerve cells of Apis mellifera ligustica brain induced by imidacloprid. 【Methods】 Apoptosis was detected in the nerve cells of honeybee brain by TUNEL labeling, cleaved Caspase-1 was detected by immunofluorescence, and the ultrastructure of nerve cells in the brain of adult worker honeybees was observed by transmission electron microscope after treatment with the sublethal dose of imidacloprid (9.90 ng/individual). 【Results】 An overall observation at seven selected sites of the brain indicated that the apoptotic rate induced by orally administrated imidacloprid at sublethal dose (9.90 ng/individual) increased with treatment time and showed significant differences between the treatment group and the control group at 9 and 12 d after treatment (P<0.01). The proportion of Caspase-1 positive cells also increased with the treatment time, and significant differences were observed at 3, 6, 9 and 12 d after treatment (P<0.01). The apoptotic rate and the proportion of Caspase-1 positive cells changed in a timedependent manner, and both showed a positive correlation. The observed ultrastructure of apoptotic nerve cells demonstrated important characteristics of apoptosis and autophagy including cell shrinkage, chromatin condensation, presence of apoptotic bodies and autophagosomes, and swollen mitochondria, some of which were enclosed by autophagic vacuoles and mitophagy occurred. 【Conclusion】 These findings suggest that at the cellular level, a sublethal dose of imidacloprid can induce nerve cell apoptosis in the brain of adult worker honeybees, and the apoptotic pathway is related to Caspase-1 and autophagy. This study provides a useful theoretical basis for estimating the harm of pesticides on non-target organisms.

Key words: Apis mellifera ligustica, neonicotinoid, imidacloprid, apoptosis, autophagy, Caspase-dependent type, ultrastructure