Abstract:
Honey bees process nectar into honey by active evaporation on the tongue and passive evaporation
involving nest ventilation and fanning behaviour, as well as enzymatic action. The elimination of
excess water from nectar carries considerable energetic costs. The concentration of the nectar load
is assumed to remain constant during transport. However, some of this water elimination may occur
before foragers return to the nest and pass their nectar loads to receiver bees. In honey bees captured
while foraging in Macadamia orchards, we show that the nectar in their crops has approximately twice
the sugar concentration of the fresh nectar in fowers. This was true for four Macadamia cultivars, with
up to 75% of the initial water content being removed. There is a further concentration increase in the
crops of returning bees captured at the hive entrance. The only possible route of water elimination
from the crop is via evaporation from the mouthparts. We calculate the savings in honey processing
costs to be on average 35 times more than the reduction in fight costs due to reduced body mass.
Pre-concentration of nectar in foraging honey bees may be widespread, and of crucial importance for
honey storage.
