Social immunity and chemical communication in the honeybee: immune-challenged bees enter enforced or self-imposed exile

Abstract

Animals living in large societies are especially vulnerable to pathogens, as their close proximity facilitates the spread of infections. Eusocial insects supplement their physiological immune systems with 'social immunity', a set of adaptations that impedes the entrance, establishment, and spread of pathogens in the colony. Here, we perform experiments with immune-challenged honey bee workers (Apis mellifera). We find that workers treated with an inert immune challenge (LPS) that mimics infection with Gram-negative bacteria quickly exit the hive, either voluntarily or by being dragged out by other workers; bees exiting the hive subsequently died. In a second experiment, we find that healthy workers treated with surface chemicals from LPS-treated bees are evicted from the hive more often than controls, indicating that immune-challenged bees produce chemical cues that cause their eviction. Thirdly, we observed pairs of bees in the lab, and found that pairs spent more time apart when one member of the pair was immune challenged, relative to procedural controls. Our findings suggest that immune-challenged bees altruistically banish themselves, and that workers evict sick individuals (which are identified via olfactory cues), putatively because of (kin) selection to limit the spread of pathogens within colonies.

Immune challenges increase network centrality in a queenless ant

“…Alternatively, infection risk can be detected through the phenotype of social partners, for example, through cues tied to those partners' immune responses to infection. For instance, experimental increases in immune activity (in the absence of pathogens) can be detected through visual [30] or chemical cues [12,15,[31][32][33][34][35]. In principle, detecting the immune status of social partners may constitute a more robust and general detection mechanism (e.g.…”

“…By simulating an infection, immune challenges allow us to study the effects of immune activation while ruling out the effects of a pathogen's virulence, manipulation of host behaviour and transmission to other colony members [3,36]. While the effects of immune challenges with various immune elicitors on the insect immune system are well characterized [37][38][39][40][41][42], few studies have quantified their effects on behaviour in social insects [15,31,33,35,43,44], and the reported behavioural effects are based on focal-individual approaches that provide limited information on colony-level responses. Here, we use automated tracking to measure both individual behaviour and patterns of interactions between all colony members.…”