Although controlled atmosphere temperature treatments are effective in controlling codling moth, Cydia pomonella (L.), in fruit, the mechanism by which this combination treatment kills the larvae is unknown. Differential scanning calorimetry was used to determine the effects of elevated temperatures, low O₂, and high CO₂ on the metabolic heat rate of fifth-instar codling moths. Total ATP levels also were determined. Metabolic heat rates in air increased from 0 to 30°C and decreased above 30°C. Heat rates measured isothermally at 23°C under decreased O₂ or increased CO₂ were lower than those in air with the lowest in 1 kPa O₂ and 1 kPa O₂ 15 kPa CO₂, Continuous temperature scans from 23 to 44.5°C under low O₂ and high CO₂ atmospheres produced lower metabolic heat rates than scans under air. Low O₂ atmospheres produced the lowest ATP levels, and high concentrations of CO₂ produced the highest ATP levels. These results indicate that heat treatments under controlled atmospheres have a dramatic effect on codling moth metabolism, low O₂ prevents ATP synthesis, and high CO₂ prevents use of ATP.