Low food stores affect dance communication and health-related gene expression in honey bees

Honey bees, Apis mellifera, are important pollinators, and they face many natural and anthropogenic challenges that affect their ability to collect the resources needed to maintain the colony. Foragers can make use of a remarkable repertoire of communication behaviours that help colonies to exploit their environment successfully. Food source availability is a key factor for colony success and, therefore, survival and reproduction. Few studies have investigated how food stores impact forager communication strategies and bee physiology. We experimentally manipulated honey stores and (1) quantified the production and following of waggle dances, (2) quantified the expression of immune-related genes using qPCR and (3) analysed fatty acids from bee abdomens using GC-MS 6 days after the experimental manipulation. We found that the number of waggle dances increased by about 60% when honey bees were starved of honey. The number of followers per dance, however, decreased, which may be due to a switch to proactive, solitary foraging or to the occurrence of more waggle dances. Waggle dance duration, the number of waggle phase followers that were followed and foraging distances were not affected by the treatments. Bees in starved colonies showed a higher expression of the gene defensin 1, which is an important predictor of overwinter survival, but there was no treatment effect on fatty acid content. Our results show that the amount of honey stored in hives affects communication behaviours and the investment in immunocompetence of bees, possibly to counter the negative health effects of nutritional stress. However, fat content does not seem to be affected in the time span of the study.