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 O2, elevated CO2, and their combinations were investigated using microcalorimetry, and mortality of pupae under elevated CO2 atmospheres was correlated with metabolic responses. The metabolic heat rate decreased slightly with decreasing O2 concentration until a critical O2 concentration (Pc) below which the heat rate decreased rapidly. The Pc increased with temperature. The percentage decreases of metabolic heat rate were comparable to the percentage decreases of O2 consumption rate (RO2) at 10, 8, 6, and 4% O2, but were smaller at 2 and 1% O2. The metabolic heat rate decreased rapidly at 20% CO2 relative to 0% CO2, with little to no further decrease between 20 and 79% CO2. The percentage decreases of RO2 under 20 and 79% CO2 at 20°C were comparable to the percentage decreases of metabolic heat rates. The additive effects of subatmospheric O2 and elevated CO2 levels on reducing metabolic heat rate were generally fully realized at combinations of ≤5% CO2 and ≥4% O2, but became increasingly overlapped as the O2 concentration decreased and the CO2 concentration increased. The high susceptibility of pupae to elevated CO2 at high temperature was correlated with high metabolic heat rate. The metabolic responses of pupae to reduced O2 concentrations included metabolic arrest and anaerobic metabolism. The net effect of elevated CO2 on the pupal respiratory metabolism was similar to that of reduced O2; however, mechanisms other than the decrease of metabolism were also contributing to the toxicity of CO2.