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.
The relations between the patterns of discontinuous gas exchange cycles (DGCs) and water loss were investigated in non-chilled diapausing pupae of the white cabbage butterfly Pieris brassicae kept at room temperature (22-24°C) in Petri dishes. An electrolytic respirometer, combined with an infrared (IR) actographic device was used for the simultaneous recordings of metabolic rate, cyclic release of carbon dioxide (bursts), passive suction inspirations (PSIs) and body movements. The patterns of cyclic gas exchange in four- and five-month-old non-chilled diapausing pupae varied individually to a considerable extent. About 40% of the pupae displayed long DGCs lasting 1-3 h, while the interburst periods were characterised by rare and almost regular large PSIs succeeding at intervals of 1-4 min. Nearly 30% of the pupae exhibited short DGCs lasting 3-5 min, while between the bursts there occurred unclear frequent gas exchange microcycles. Standard metabolic rate (SMR) did not reveal significant differences between long DGCs and short DGCs ranging from 32-56 (mean 47.6 ± 4.6) ml O2 g-1 h-1, and 28-61 (mean 44.95 ± 5.3) ml O2 g-1 h-1, respectively. The mentioned levels of SMR were characteristic of diapausing pupae.
Water loss in pupae with long DGCs was determined gravimetrically to be 0.29 ± 0.1 mg g-1 day1. At the same time, water loss in pupae that showed only short DGCs and irregular microcycles was 1.73 ± 0.31 mg g-1 day-1, which was significantly higher than in individuals characterised by long DGCs. We suggest that water loss in the non-chilled diapausing pupae may depend significantly on the patterns of cyclic gas exchange: long cycles and rare but deep PSIs exerted a marked water conserving effect.
Adults of Colorado potato beetle Leptinotarsa decemlineata are very active at room temperature, and their almost continuous struggling in the respirometer prevents the measurements of the patterns of gas exchange, body movements and heartbeat. The tonic immobility of beetles was evoked by light flashes and by shaking as external stimuli. The immediate reaction to these stimuli was the reflexive closing of the spiracles and the cessation of CO2 release for some minutes, which was followed by a large burst of this gas. The state of the evoked tonic immobility did not influence heartbeat and abdominal pulsations, but the periodically -occurring abdominal-thoracic pumping movements stopped for 2-5 minutes. During the periods of pumping ventilation the metabolic rate was increased about two times.The state of tonic immobility evoked by light flashes lasted 2-6 minutes, but when shaking was applied as a stimulus complete immobility was about two times longer.