Death pheromones triggering hygienic behavior in honey bees (Apis mellifera L.)

Eusocial insects live in teeming societies with thousands of their kin. In this crowded environment, workers combat disease by removing or burying their dead or diseased nestmates. For honey bees, we found that hygienic brood-removal behavior is triggered by two odors - β-ocimene and oleic acid - which are released from brood upon death. β-ocimene is a co-opted pheromone that normally signals larval food-begging, whereas oleic acid is a conserved necromone across arthropod taxa. Interestingly, the odor blend induces hygienic behavior more consistently than either odor alone. We suggest that the volatile β-ocimene flags the attention of hygienic workers, while oleic acid is the death cue, triggering removal. Hygienic bees detect and remove brood with these odors faster than non-hygienic bees, and both molecules are ligands for hygienic behavior-associated odorant binding proteins. These are key mechanistic insights into some of the molecular interactions that govern disease resistance in a domesticated eusocial insect.