Eddy M. De Robertis

bees at two sites where hives were surrounded by dense occurrences of aloes. Nectar from this plant is considered to be important for bee honey reserves, although it is known to be dilute compared with other sources. The researchers measured the crop volumes of bees at foraging sites around the aloe flowers and also at the entrance to their hives. They found that there was no significant difference in the crop volumes of bees at the flowering site and those entering the hive. However, when the researchers looked at the concentration of sugar, they found a considerable increase in the crop values of bees around the flowers, compared with the nectar within the flowers themselves. The sugar concentration of crop contents was also found to be similar in those bees entering the hives. The crop content of bees departing the hive to gather more nectar was also found to be concentrated: this provides the food source for the foraging bees. So how do the bees concentrate the nectar they are gathering? Increased concentration of crop contents has previously been observed in solitary mason bees and carpenter bees. But neither the dilution of haemolymph in solitary bees or the excretion of dilute fluids by honeybees when transporting nectar has been found. “Evaporation from the mouthparts provides the only explanation,” the authors conclude. When heated under laboratory conditions, honeybees repeatedly regurgitate a droplet of nectar onto the proboscis and then withdraw the cooled droplet to achieve evaporative cooling of the head. In addition to the cooling effect, the process concentrates the crop contents of bees and is used by receiver bees to ripen honey before depositing it in cells. “Honeybees foraging on aloes are likely to be evaporating dilute nectar on their tongues as they move between flowers and on the return flight to the hive,” the researchers report. “The increased concentration is dramatic owing to the small nectar volumes carried and the very dry atmosphere prevailing during flowering,” they write. It’s a potentially neat way of lightening the load but perhaps misleads hive-based workers as to the true quality of this winter nectar source.