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), elevated CO(2), and their combinations were investigated using microcalorimetry, and mortality of pupae under elevated CO(2) atmospheres was correlated with metabolic 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(c) increased with temperature. The percentage decreases of metabolic heat rate were comparable to the percentage decreases of O(2) consumption rate (RO(2)) at 10, 8, 6, and 4% O(2), but were smaller at 2 and 1% O(2). The metabolic heat rate decreased rapidly at 20% CO(2) relative to 0% CO(2), with little to no further decrease between 20 and 79% CO(2). The percentage decreases of RO(2) under 20 and 79% CO(2) at 20 degrees C were comparable to the percentage decreases of metabolic heat rates. The additive effects of subatmospheric O(2) and elevated CO(2) levels on reducing metabolic heat rate were generally fully realized at combinations of </=5% CO(2) and >/=4% O(2), but became increasingly overlapped as the O(2) concentration decreased and the CO(2) concentration increased. The high susceptibility of pupae to elevated CO(2) 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 CO(2) on the pupal respiratory metabolism was similar to that of reduced O(2); however, mechanisms other than the decrease of metabolism were also contributing to the toxicity of CO(2).