Oxygen uptake by convection and diffusion in diapausing moth pupae (Attacus atlas)

We investigated O-2 uptake of diapausing Attacus atlas pupae during the "fluttering'' period of a DGC using plethysmometry and flow through respirometry in combination with tracheal pressure and tracheal PO2 measurement. Within the initial phase of the fluttering period, convection of air during brief spiracle openings (< 1s) allowed oxygen uptake mainly by convection with certain amounts of air sucked into the highly compliant tracheal system. Pressure rise rates may reach 2200 Pa s(-1) and maximum air flow rate into the tracheal system can thus be 50 mu l s(-1). The total retention of CO2 during the passive suction ventilation could be proved at maximum tracheal pressures below -6.27 Pa. Later in the fluttering period, the spiracular conductance increases, both with opening duration and frequency, leading to an O-2 uptake mainly by diffusion while CO2 may be released in small peaks. Our results indicate a substantial contribution of the "passive suction ventilation'' with its ability to conserve water to oxygen uptake only in the beginning of the fluttering period while diffusion is the dominating mechanism of gas exchange in the main proportion of the fluttering period. (c) 2004 Elsevier B.V. All rights reserved.