Brood pheromone stimulates pollen foraging in honey bees (Apis mellifera)

Foraging and the mechanisms that regulate the quantity of food collected ar e important evolutionary and ecological attributes for all organisms. The d ecision to collect pollen by honey bee foragers depends on the number of la rvae (brood), amount of stored pollen in the colony, as well as forager gen otype and available resources in the environment. Here we describe how broo d pheromone (whole hexane extracts of larvae) influenced honey bee pollen f oraging and test the predictions of two foraging-regulation hypotheses: the indirect or brood-food mechanism and the direct mechanism of pollen-foragi ng regulation. Hexane extracts of larvae containing brood pheromone stimula ted pollen foraging. Colonies were provided with extracts of 1000 larvae (b rood pheromone), 1000 larvae (brood), or no brood or pheromone. Colonies wi th brood pheromone and brood had similar numbers of pollen foragers, while those colonies without brood or pheromone had significantly fewer pollen fo ragers. The number of pollen foragers increased more than 2.5-fold when col onies were provided with extracts of 2000 larvae as a supplement to the 100 0 larvae they already had. Within 1 h of presenting colonies with brood phe romone, pollen foragers responded to the stimulus. The results from this st udy demonstrate some important aspects of pollen foraging in honey bee colo nies: (1) pollen foragers appear to be directly affected by brood pheromone , (2) pollen foraging can be stimulated with brood pheromone in colonies pr ovided with pollen but no larvae, and (3) pollen forager numbers increase w ith brood pheromone as a supplement to brood without increasing the number of larvae in the colony. These results support the direct-stimulus hypothes is for pollen foraging and do not support the indirect-inhibitor, brood-foo d hypothesis for pollen-foraging regulation.