Metabolic response of Platynota stultana pupae during and after extended exposure to elevated CO2 and reduced O2 atmospheres

The metabolic response of Platynota stultana pupae to elevated CO2 and reduced O-2 atmospheres was measured using microcalorimetry. Initial measurements at 20 degreesC immediately upon placement in controlled atmosphere indicated a decrease in metabolic heat rate (MHR) of 27, 45, 56, 56, and 72% in an atmosphere of 5, 10, 20, 40, and 79% CO2, respectively, and a decrease of 20, 50, 66 and 100% under 6, 2, 1, and 0% O-2. With extended exposure to controlled atmospheres, MHR increased under 5, 10, and 20% CO2 and 6 and 2% O-2; however, the increase was greater and occurred more rapidly with lower CO2 and higher O-2 concentration. The MHR at 40 and 79% CO2 remained at the initial reduced level for 8 and 6 days, respectively, then decreased with longer exposure. The MHR of pupae held under 1 and 0% O-2 remained at the initial reduced level for 22 days. Upon transfer to air, the MHR of pupae increased from the reduced levels and then decreased. When the MHR decreased by no more than 30%, as a result of controlled atmosphere treatment, the pupae still developed into adults. However, when the MHR decreased by more than 50%, the energy supply was insufficient and the pupae died. Pupa mortality was comparable between 5% CO2 and 6% O-2, and 10% CO2 and 2% O-2. The MHR was reduced less under 20% CO2 than under 2 or 1% O-2; however, the pupae were more susceptible to 20% CO2 than 2 or 1% O-2. These and other data indicate an increased toxicity of high CO2 over low O-2 atmospheres that may be related to an increase in membrane permeability as a result of CO2 treatment. (C) 2001 Elsevier Science Ltd. All rights reserved.