Elevated atmospheric CO2 expected in the near future as a consequence of increasing emissions will alter the quantity and quality of plant foliage, which in turn can influence the growth and development of insect herbivores. Feeding trials with two foliage feeding insect species, Achaea janata and Spodoptera litura were conducted using foliage of castor plants grown under four concentrations of CO2, viz. 700 ppm CO2 inside open top chamber (OTC), 550 ppm CO2 inside OTC, ambient CO2 (350 ppm) inside OTC and ambient CO2 in the open.