Controlled atmospheres are a promising alternative to methyl bromide for postharvest and quarantine insect control. With controlled atmospheres, the levels of carbon dioxide (CO₂) and oxygen (O₂) are regulated in an enclosed area. Elevated CO₂ and low O₂ atmospheres have both been used, separately and in combination, with varying degrees of control success. Developing insecticidal controlled atmospheres typically takes a long time because the ratio of CO₂ and O₂ necessary to kill insects and timing of application will differ. New testing must be done for every insect pest and life stage with each commodity. The overall goal of our research is to understand the mechanisms of CO₂ mortality. We believe that by answering the question “Why do they die?” we can more quickly choose an insecticidal atmosphere and increase mortality. We are presenting results testing one hypothesis that elevated CO₂ lowers energy levels, leading to death. Our study insect is a quarantine pest on grapes to Australia, Platynota stultana. Additionally, an insect resistant to controlled atmospheres, Pseudococcus maritimus, and one susceptible, P. viburni, are being studied to determine if resistance to controlled atmospheres is due to the ability to maintain a stable metabolic rate while being treated. Results show that as CO₂ concentrations increase, adenosine triphosphate (ATP) levels decrease. However, the energy level of the insect is not necessarily indicative of mortality. The mealybug results suggest that an initial low metabolism may be beneficial to resisting controlled atmospheres.