Interrelations of gas exchange cycles, body movements and heartbeats in the foragers of bumblebee Bombus terrestris (Hymenoptera: Apidae) at low temperatures

Rhythmic body movements, cyclic gas exchange and heart activity were studied at low temperature (mostly at 5°C) in bumblebee Bombus terrestris foragers. Simultaneous measurements by means of an electrolytic respirometer combined with an optical system by infrared radiation, revealed a co-ordination between discontinuous gas exchange cycles and body rhythmic movements. No distinct correlation was found between intermittent heart activity and body movements. The carbon dioxide bursts were actively ventilated by abdominal vigorous pumping movements. These bursts followed each other with intervals of 25-30 minutes.The periods of heart activity regularly alternated with heart pauses. The frequency of the heartbeat was similar to that of the weak abdominal pulsations (0.2-0.25 Hz) which were imperceptible with the naked eye. All bumblebees displayed abdominal pulsations which were independent of vigorous pumping movements. In bumblebee B. terrestris foragers haemolymph oscillation was assumed at 5°C, as is known in the honeybee and some other Bombus species.