Atmospheric levels of carbon dioxide (CO₂) have been increasing steadily over the last century. Plants grown under elevated CO₂ experience physiological changes that influence their suitability as food. Previous studies have found increased insect herbivory on plants grown under elevated CO₂. To determine effects of consuming foliage of soybean (Glycine max) grown under elevated CO₂ on adult survivorship and fecundity, Japanese beetles (Popillia japonica Newman) were fed for the duration of their adult lives leaves grown under elevated CO₂ (550 μmol/mol), under ambient atmosphere (370 μmol/mol), or grown under ambient atmosphere but supplemented with a solution of sugars. To determine effects of a diet of foliage grown under elevated ozone (O₃), another anthropogenic gaseous pollutant, beetles in the laboratory were fed soybean leaves grown under elevated CO₂, elevated O₃, or a combination of both elevated gases. Leaf tissue was also analyzed for longevity-enhancing antioxidants, because increases in dietary antioxidants can increase lifespan. Lifespan of Japanese beetles was prolonged by 8–25% when fed foliage developed under elevated CO₂, but consuming foliage that had taken up sugars to approximately the same level as foliage grown under elevated CO₂ had no effect on fecundity or longevity. Females consuming elevated CO₂ foliage laid approximately twice as many eggs as females fed foliage grown under ambient conditions. Consuming foliage grown under elevated O₃ had no effect on fecundity. No significant differences in total antioxidant content of foliage from ambient and elevated CO₂ conditions were detected. Although the precise mechanism is unclear, by altering components of leaf chemistry other than sugar content, elevated CO₂ may increase populations of Japanese beetles and their impact on crop productivity.