Response of an insect herbivore to host plants grown in carbon dioxide enriched atmospheres

Rising atmospheric carbon dioxide concentration is expected to increase plant productivity, but little evidence is available regarding effects on insect feeding or growth. Larvae of the soybean looper, a noctuid moth, were fed leaves of soybean plants grown under three carbon dioxide regimes (350, 500 and 650 μl·l^-1). Larvae fed at increasingly higher rates on plants from elevated carbon dioxide atmospheres: 30% greater on leaves from the 650 μl·l^-1 treatment than on leaves from the 350 μl·l^-1 treatment. When variation in larval feeding was related to the leaf content of nitrogen and water, there was no significant remaining effect of carbon dioxide treatment. The principal effect on herbivores of increasing the carbon supply of leaves appeared to be reduction of leaf nutrient concentration. This study suggests that feeding by herbivores on the leaves of C₃ plants may increase as the level of atmospheric carbon dioxide rises.