Social benefits require a community: the influence of colony size on behavioral immunity in honey bees

Abstract

Emergent properties of eusocial insect colonies (e.g., nest architecture and defense) highlight benefits of group living. Such emergent properties, however, may only function as a benefit if the group is large enough. We tested the effect of group size on colony-level fever in honey bees. When a colony is infected with Ascosphaera apis, a heat-sensitive brood pathogen, adult bees raise the temperature to kill the pathogen and keep brood disease free. In relatively large colonies, we show a rhythm to honey bee fever: colonies inoculated with A. apis generated a fever in the afternoon and at night but not in the morning. In comparison, relatively small colonies did not generate a fever following inoculation, although they invested more in thermoregulation on a “per bee” basis than control colonies. Thus, in small colonies, honey bee fever could be regarded as a cost of group living: individuals futilely exerted valuable energy towards fighting a pathogen.