A method for identifying water foraging bees by refractometer analysis: a spotlight on daily and seasonal water collecting activities of Apis mellifera L.

摘要

The current discussion about the relevance of guttation as a water source for honey bees (Apis mellifera L.) draws attention to the activity of water foraging bees. However, due to the wide foraging range, field observations of water foraging bees are difficult to carry out. Therefore, samples of returning bees were collected in front of the entrance early in the morning as well as during the day in summer and autumn 2010. In the laboratory, honey sacs of bees without pollen or propolis were examined. Honey sac samples with a weight of >=0.005 g were classified as successful foragers. For the determination of water or nectar foragers, the honey sac contents of successful foragers were analyzed with a refractometer. Due to the dilution and the precision of the refractometer, an accuracy of 5% was possible. Based on the known range of sugar concentrations in nectars, the analyzed samples were divided into nectar foragers (25-65% sugar) and water foragers (0-15% sugar). The study reveals that nectar and water foraging bees can be discriminated by analyzing the honey sac extracts with a refractometer. In autumn, the water demand of honey bee colonies is almost exclusively covered by water collection, whereas during summer nectar is mainly used as a substitute for water. In general, water collection is not restricted to certain times of the day.Digital Object Identifier http://dx.doi.org/10.1007/s00003-012-0799-3