Division of labors shifts in response to brood age in Apis mellifera

For many years, researchers have known that brood stimulates pollen foraging.  The nutritional and thermoregulatory needs of brood shift as they age, as do the pheromone profiles emitted by the developing young. If honey bees can recognize different aged larvae and their divergent nutritional needs, they may adjust their foraging behavior accordingly. We tested whether young larvae, dependent on protein rich brood food, and the predominant young larval pheromone, e-beta-ocimene (e-β), release foraging behavior biased toward protein rich pollen. 

            In the first experiment nucleus colonies (nucs) were set up from a package of mixed aged bees. The nucs were provided with 1 comb of honey, 1 empty comb and 1 of four different brood treatments: 1) young larvae 2) old larvae 3) capped brood or 4) empty comb. Foraging behavior was monitored the next morning in multiple 5 minute intervals. Entrances were blocked and 50 foragers were collected from each nuc and their foraging load measured for pollen mass, nectar load and nectar concentration. This experiment was replicated 4 times. Young larvae stimulated a significantly higher ratio of pollen foraging than old larvae, capped brood or no brood. Although there were no significant differences in individual pollen or nectar loads between foragers of the different brood treatments, hives with young larvae collected significantly more pollen and had significantly fewer foragers returning empty to the hive.

In the second experiment packages were established in five frame nuc boxes. The nucs were provided with 1 comb of honey, 1 empty comb and 1 of three different brood treatments: 1) young larvae, 2) 10,000 larval equivalents of e-β, or 3) no brood. Foraging was monitored as above. Both young larvae and e-β resulted in significantly higher proportion of pollen foragers compared to no brood.

Thus both young larvae and e-β release pollen foraging. Additional experiments are in progress to determine the priming effects of both young larvae and e-β and the complete results are pending. Initial results include suppression of ovary development by e-β, independent of ovary size compared to controls. e-β also stimulates increased protein consumption in cage trials.