The western honeybee (Apis mellifera) is essential for the global economy due to its important role in ecosystems and agriculture as a pollinator of numerous flowering plants and crops. Pesticide abuse has greatly impacted honeybees and caused tremendous loss of honeybee colonies worldwide. The reasons for colony loss remain unclear, but involvement of pesticides and pathogen-pesticide interactions has been hypothesized. Histone deacetylase inhibitors (HDACis) inhibit the activity of histone acetylase, which causes the hyperacetylation of histone cores and influences gene expression. In this study, sodium butyrate, an HDACi, was used as a dietary supplement for honeybees; after treatment, gene expression profiles were analyzed using quantitative PCR. The results showed that sodium butyrate up-regulated genes involved in anti-pathogen and detoxification pathways. The bioassay results showed that honeybees treated with sodium butyrate were more tolerant to imidacloprid. Additionally, sodium butyrate strengthened the immune response of honeybees to invasions of Nosema ceranae and viral infections. We also performed a bioassay in which honeybees were exposed to pesticides and pathogens. Our results provide additional data regarding the mechanism by which honeybees react to stress and the potential application of HDACis in beekeeping.

Apis mellifera plays crucial roles in maintaining the balance of global ecosystems and stability of agricultural systems by helping pollination of flowering plants, including many crops. In recent years, this balance has been disrupted greatly by some pesticides, which results in great losses of honeybees worldwide. Previous studies have found that pesticide-caused memory loss might be one of the major reasons for colony loss. Histone deacetylase inhibitors (HDACis) are chemical compounds that inhibit the activity of histone deacetylases and are known to cause hyperacetylation of histone cores and influence gene expression. In our study, the HDACi sodium butyrate was applied to honeybees as a dietary supplement. The effect of sodium butyrate on the expression profiles of memory-related genes was analysed by quantitative reverse transcription PCR. The results revealed that this HDACi had up-regulation effects on most of the memory-related genes in bees, even in bees treated with imidacloprid. In addition, using the proboscis extension reflex to evaluate olfactory learning in bees, we found that this HDACi boosted the memory formation of bees after impairment owing to imidacloprid exposure. This study investigated the association between gene expression and memory formation from an epigenetic perspective. Additionally, we further demonstrate the possibility of enhancing bee learning using HDACis and provide initial data for future research.