Host plant (Ricinus communis Linn.) mediated effects of elevated CO2 on growth performance of two insect folivores.

Elevated atmospheric CO 2 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 CO 2 , viz. 700 ppm CO 2 inside open top chamber (OTC), 550 ppm CO 2 inside OTC, ambient CO 2 (350 ppm) inside OTC and ambient CO 2 in the open. Biochemical analysis of foliage revealed that plants grown under elevated CO 2 had lower N, and higher C, C/N ratio and polyphenols. Compared to the larvae fed on ambient CO 2 foliage, the larvae fed on 700 and 550 ppm CO 2 foliage exhibited greater consumption. Larval duration also increased by two days. The 700 and 550 ppm CO 2 foliage was more digestible with higher values of approximate digestibility. The relative consumption rate of larvae increased whereas the efficiency parameters, viz. efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD), and relative growth rate (RGR) decreased in case of larvae grown on 700 and 550 ppm CO 2 foliage. The consumption and weight gain of the larvae were negatively and significantly influenced by leaf nitrogen, which was found to be the most important factor affecting consumption and growth of larvae.