Sublethal acetamiprid exposure induces immunity, suppresses pathways linked to juvenile hormone synthesis in queens and affects cycle-related signaling in emerging bees

Abstract

Acetamiprid is the only neonicotinoid registered in the European Union because the risks of neonicotinoids to honey bees and other pollinators are strictly regulated. Herein, we orally exposed honey bee colonies to sublethal concentrations of acetamiprid (20 μg/L) under isolated conditions. After one month of continuous exposure, the emerging bees and queens were collected and analyzed via high-throughput label-free quantitative proteomics using a data-independent acquisition strategy. Six and 34 significantly differentially expressed proteins (DEPs) were identified in the emerging bees and queens, respectively. Mrjp3 was the only DEP found in both sample types/castes, and its opposite regulation illustrated a differential response. The DEPs in the emerging bees (H/ACA RNP, Rap1GAP, Mrjp3, and JHE) suggested that sublethal exposure to acetamiprid affected cell cycle-related signaling, which may affect the life history of workers in the colony. The DEPs with increased levels in queens, such as Mrjps 1–4 and 6–7, hymenoptaecin, and apidaecin 22, indicated an activated immune response. Additionally, the level of farnesyl pyrophosphate synthase (FPPS), which is essential for the mevalonate pathway and juvenile hormone biosynthesis, was significantly decreased in queens. The impaired utilization of juvenile hormone in queens supported the identification of additional DEPs. Furthermore, the proteome changes suggested the existence of increased neonicotinoid detoxification by UDP-glucuronosyltransferase and increased amino acid metabolism. The results suggest that the continuous exposure of bee colonies to acetamiprid at low doses (nanograms per gram in feed) may pose a threat to the colonies. The different exposure routes and durations for the emerging bees and queens in our experiment must be considered, i.e., the emerging bees were exposed as larvae via feeding royal jelly and beebread provided by workers (nurse bees), whereas the queens were fed royal jelly throughout the experiment. The biological consequences of the proteomic changes resulting from sublethal/chronic exposure require future determination.