Abstract
Honeybees need water for different purposes, to maintain the osmotic homeostasis in adults as well as to dilute stored honey and prepare liquid food for the brood. Water is also used for cooling of the hive. Foraging in endothermic insects is energy-intensive and the question arises how much energy bees invest in a resource without any metabolically usable energy. We investigated the energy demand of water collecting bees under natural conditions. The thermoregulation and energetic effort was measured simultaneously in a broad range of experimental ambient temperatures (Ta = 12–40 °C). The thorax temperature as well as the energetic turnover showed a great variability. The mean Tthorax was ranging from ~ 35.7 °C at 12 °C to nearly 42.5 °C at 40 °C. The energy turnover calculated from CO2-release was highest at a Ta of 20 °C with about 60 mW and lowest at 40 °C with about 22 mW per bee. The total costs during collection decreased from 10.4 J at 12 °C to 0.5 J at 40 °C. The energetic effort of the water collectors was comparable with that of 0.5 M sucrose foraging bees. Our investigation strongly supports the hypothesis that the bees’ motivational status determines the energetic performance during foraging.
Highlights
Besides pollen and nectar, water is an essential resource for the honeybee colony
We investigated for the first time the energetic demand of water collecting honeybees to see how much energy they are willing to invest in a resource without any metabolically usable energy content
In the course of our comprehensive investigation, we determined the energetic effort of honeybees at a water source
Summary
Water is an essential resource for the honeybee colony. Water is needed to maintain the osmotic homeostasis in adult bees, and to dilute stored honey and prepare liquid food for the brood. We compared the energetic demand of water collecting bees with that of sucrose foraging bees (Stabentheiner and Kovac 2016). For body temperature and respiration measurements, bees collected water from a small plastic cup. In the first series of experiments, body temperature and respiration were measured in different bees, but at the same time at identical water sources positioned close to each other (about 50 cm, for methodical details see Stabentheiner et al 2012). The upper part of the cylindrical measurement chamber was connected to the objective of an infrared camera (FLIR ThermaCam SC2000 NTS, Fig. 1a) This allowed the thermographic measurement of the bees’ body surface temperature and the observation of their behaviour during foraging. The experiments of the water collectors and the sucrose foragers (Stabentheiner and Kovac 2016) were conducted at the same location
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