Colony-level impacts of immune responsiveness in honey bees, Apis mellifera.

Social insects have evolved both communal and individual traits that reduce the impacts of their numerous parasites and pathogens. Among the individual traits, innate-immune responses have the potential to reduce both individual mortality and the spread of pathogens among colony members. An understanding of the costs and benefits of such responses can provide a more complete understanding of a primary risk of social life, horizontal disease transmission among colony members. Here we assess the impacts of individual immunity on colony-level disease in honey bee (Apis mellifera) colonies following exposure to an important bacterial pathogen (Paenibacillus larvae subsp. larvae, cause of the disease American foulbrood). Colony-level disease rates were negatively correlated with the immune responsiveness of colony members, as assessed by larval transcript levels for the gene encoding the antibacterial peptide abaecin. Concomitantly, colonies whose members mounted a stronger abaecin response showed significantly lower productivity, indicating a colony-level cost to this immune response. The results show considerable variation across colonies in an immune trait important for survival, and point toward a significant trade-off between this trait and colony productivity.