Updated project metadata. Updated publication reference for PubMed record(s): 31823732. Diapause is a key life-history event characterised by arrested development, suppressed metabolism and increased stress tolerance. This state allows an organism to avoid prolonged periods of harsh and inhospitable environmental conditions. For species where only mated female adults undergo diapause, mating is performed prior to diapause. Mating can have a profound effect on the behaviour and physiology of females resulting in changes to the expression of key biological processes, including immunity. However, our understanding of how mating impacts long-term immunity and whether these effects persist throughout diapause is currently limited. Here we explored proteomic changes in the haemolymph of the ecologically important pollinator, Bombus terrestris. B. terrestris queens mate prior to diapause (a non-feeding arrest of development that can last 6-9 months). Using mass-spectrometry-based proteomics, we quantified changes in the pre-diapause queen haemolymph after mating, as well as the subsequent protein expression of mated queens during and post-diapause. Our results provide clear molecular evidence for the consequences and benefits of mating at the immune level through the selective increased abundance of antimicrobial peptides that are sustained throughout diapause. In addition our results provide novel insights into the molecular mechanisms by which bumblebees prepare for, survive, and recover from diapause, insights that may have implications for our general understanding of these processes in other insect groups.