Date of this Version
Bee World • VOL 94 • March 2017
Understanding the complexities of social insect immunity, that is, how insects combat pathogens, parasites and pests, is a fundamental question that not only has broad applications for understanding disease dynamics in social groups (Fefferman & Traniello, 2008) (e.g., human societies) but also practical benefits for improving honey bee stocks for increased health and productivity. When we first consider the concept of immunity in any organism, the tendency is to think at the level of the individual organism and focus on physical barriers (e.g., the honey bee cuticle) and individual physiological defenses that are largely induced in response to pathogens that get past the initial defenses (e.g., antimicrobial peptides in the bee hemolymph). For honey bees (specifically Apis mellifera in this discussion) and other social insects, however, the colony is often the unit of evolutionary selection (Seeley, 1997). Combined efforts of individual honey bees promote colony productivity and survival; thus individuals in that colony survive to successfully spread their genetics through subsequent generations via the production of drones, swarms, and queens.
In many ways, immunity in social insects exemplifies the superorganism concept, whereby there is an immune system in individual bees, but there is also a colony-level immune system. Both function to promote survival not only of an individual bee but also of the colony. Given the reduction in immune genes that has now been noted for honey bees and Hymenoptera in general (Barribeau et al., 2015; Evans et al., 2006; Gadau et al., 2012; Simola et al., 2013), it seems as though the evolution of numerous colony-level, largely behavioral mechanisms has occurred either to compensate for the reduced investment in physiological immunity or as a result of the reliance on colony-level defenses relaxing the selection pressure for a stronger individual immune defense (Harpur & Zayed, 2013).