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

Abstract

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. Biochemical analysis of foliage revealed that plants grown under elevated CO2 had lower N, and higher C, C/N ratio and polyphenols. Compared to the larvae fed on ambient CO2 foliage, the larvae fed on 700 and 550 ppm CO2 foliage exhibited greater consumption. Larval duration also increased by two days. The 700 and 550 ppm CO2 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 CO2 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.