Thermoregulation of water collecting honey bees (Apis mellifera)

Honey bees (Apis mellifera carnica, Apidae, Hymenoptera) visited a pond in order to collect water. During their stays at the pond the body surface temperature of water foragers was measured using contactless thermography. Irrespective of the ambient temperature (TA) which ranged from 13.6 to 27.2°C, the water carriers reached thoracic temperatures of 36–38.8°C (mean values of the measuring periods). The maximum thoracic value of an individual bee was 44.5°C. At higher TA (20.9–27.2°C) head and abdomen were only about 3°C and 2°C on the average higher than the surroundings, respectively. In the lower range of TA (13.6–16.6°C), however, the bees warmed their heads up to 29.2°C (13°C above TA) and the abdomen up to 23.3°C (7.1°C above TA; mean values of the measuring periods). ad and abdomen were even provided independently of one another with heat from the thorax. At a higher TA only little heat came from the heated thorax into the abdomen, at a cooler TA (13.6–16.6°C) more heat reached the abdomen. In all probability, at a higher TA only a small amount of haemolymph was pumped from the thorax into the abdomen; the most warm blood probably circulated in the head-thorax area. The average duration of stays at the pond decreased linearly from 110 to 42 s with rising TA. Head and thorax showed great fluctuations of temperature. For example, the head was heated by 4.6°C within 25 s, the thorax by 6.1°C within 30 s. rs drinking sucrose solution are known to increase their thoracic temperature with rising concentration of the sucrose solution. The water foragers had thoracic temperatures similar to that of bees feeding on 0.5 molar sucrose solution. It is hypothesized that the foraging motivation of both groups was similar and therefore they regulated their thoraces at the same temperature level.