If the carbon dioxide (CO₂) concentration in the atmosphere changes in the future, as predicted, it could influence crops and insect pests. The growth and development of the tobacco caterpillar, Spodoptera litura (Fabricius) (Noctuidae: Lepidoptera), reared on peanut (Arachis hypogea L.) foliage grown under elevated CO₂ (550 ppm and 700 ppm) concentrations in open top chambers at Central Research Institute for Dryland Agriculture, Hyderabad, India, were examined in this study. Significantly lower leaf nitrogen, higher carbon, higher relative proportion of carbon to nitrogen and higher polyphenols content expressed in terms of tannic acid equivalents were observed in the peanut foliage grown under elevated CO₂ levels. Substantial influence of elevated CO₂ on S. litura was noticed, such as longer larval duration, higher larval weights, and increased consumption of peanut foliage by S. litura larvae under elevated CO₂ compared with ambient CO₂. Relative consumption rate was significantly higher for S. litura larva fed plants grown at 550 and 700 ppm than for larvae fed plants grown at ambient condition. Decreased efficiency of conversion of ingested food, decreased efficiency of conversion of digested food, and decreased relative growth rate of larvae was observed under elevated CO₂. The present results indicate that elevated CO₂ levels altered the quality of the peanut foliage, resulting in higher consumption, lower digestive efficiency, slower growth, and longer time to pupation (one day more than ambient).