Metabolic response of Platynota stultana pupae to controlled atmospheres and its relation to insect mortality response

The metabolic responses of Platynota stultana pupae to reduced O-2, elevate d CO2, and their combinations were investigated using microcalorimetry, and mortality of pupae under elevated CO, atmospheres was correlated with meta bolic responses. The metabolic heat rate decreased slightly with decreasing O-2 concentration until a critical O-2 concentration (P-c) below which the heat rate decreased rapidly. The P, increased with temperature. The percen tage decreases of metabolic heat rate were comparable to the percentage dec reases of O-2 consumption rate (RO2) at 10, 8, 6, and 4% O-2, but were smal ler at 2 and 1% O-2. The metabolic heat rate decreased rapidly at 20% CO2 r elative to 0% CO2, with little to no further decrease between 20 and 79% CO 2. The percentage decreases of RO2 under 20 and 79% CO2 at 20 degrees C wer e comparable to the percentage decreases of metabolic heat rates, The addit ive effects of subatmospheric O-2 and elevated CO2 levels on reducing metab olic heat rate were generally fully realized at combinations of less than o r equal to 5% CO2 and 4% O-2, but became increasingly overlapped as the O-2 concentration decreased and the CO2 concentration increased. The high susc eptibility of pupae to elevated CO, at high temperature was correlated with high metabolic heat rate. The metabolic responses of pupae to reduced O-2 concentrations included metabolic arrest and anaerobic metabolism. The net effect of elevated CO2 on the pupal respiratory metabolism was similar to t hat of reduced O-2; however, mechanisms other than the decrease of metaboli sm were also contributing to the toxicity of CO2. (C) 2000 Elsevier Science Ltd. All rights reserved.