Investigating the role of pheromones in mediating social behavior in bumble bees (Bombus impatiens)

Reproductive division of labor is a hallmark of eusociality, but proximate mechanisms establishing this have only been identified in some species. Bumble bees are widely used models for social behavior, but surprisingly mechanisms regulating queen dominance over reproduction are  unknown. When isolated from the queen workers become reproductively active and lay haploid eggs that develop into males. We investigated if volatile compounds produced by the queen play a role in the competition for reproduction. We developed a “reduced colony” system in which three callow (one-day old) workers received airflow from a cage containing a queen, brood and three callow workers. Within this chamber the queen inhibited worker reproduction as in a full sized colony. However, workers exposed to airflow from the reduced colonies were able to fully activate their ovaries and lay eggs. A mesh experiment was then developed to determine if a queen could inhibit reproduction through limited contact with workers. A wooden cage was separated into two compartments by a mesh screen that allowed antennal contact between bees on each side. Workers in direct contact with the queen were again completely reproductively inhibited. Workers that had limited contact with the queen were able to fully activate their ovaries and lay eggs. These data suggest that reproductive inhibition is dependent on direct queen contact. Workers in full contact with the queen were always reproductively inhibited while workers exposed to air from reduced colonies and with limited queen contact (antennation) became reproductively active.