Rhythms of passive and active ventilation, and circulation recorded in diapausing pupae of Mamestra brassicae using constant volume respirometry
Abstract
Abstract The periodically occurring convective inflow of air into the tracheal system, or passive suction ventilation, together with the cyclic bursts of release of CO2 and active ventilation, is recorded in diapausing pupae of Mamestra brassicae. A constant volume respirometer combined with an opto-cardiograph-actograph is used. In all pupae with a metabolic rate of 0.025–0.054 mL g−1 h−1, the bouts of almost imperceptible abdominal contractions are recorded during the bursts of carbon dioxide release and this mode of active ventilation is qualified as extracardiac haemocoelic pulsations. The pupae whose metabolic rate is 0.052–0.075 mL−1 g−1 h−1 show more vigorous abdominal contractions. The results demonstrate that, in diapausing pupae, characterized with low metabolic rates, both passive suction ventilation, referred to also as passive suction inspiration, and active ventilation occurs. In approximately 50% of the pupae, each gas exchange microcycle during the interburst periods begins with a miniature PSI followed by a microburst of CO2 release; in approximately 30% of the individuals, passive suction inspirations occur separately from CO2 microbursts; in the remaining pupae, miniature ones without microbursts of CO2 are recorded. A typical event is heartbeat reversion: in longer periods, the heart peristalses are directed forward (anterograde of heartbeat) and, in shorter periods, the heart peristalses are directed backward (retrograde of heartbeat). At 0 °C, the cyclic release of CO2 and miniature passive suction inspirations during the interburst periods are preserved at lower frequencies but active ventilation is lost.