Response of multiple generations of semilooper, Achaea janata feeding on castor to elevated CO2.

The growth, development and consumption of four successive generations of semilooper, Achaea janato reared on castor (Ricinus communis L.) foliage grown under elevated carbon dioxide (550 and 700 parts per million ) concentrations in open top chambers were estimated at Hyderabad, India. Significantly lower leaf nitrogen, higher carbon, higher relative proportion of carbon to nitrogen (C: N) and higher polyphenols expressed in terms of tannic acid equivalents were observed in castor foliage under elevated CO2 levels. Significant influence on life history parameters of A. jonata viz., longer larval duration, increased larval survival rates and differential pupal weights in successive four generations were observed under elevated over ambient CO2 levels. The consumption per larva under elevated CO2 increased from first to fourth generation. An increase in approximate digestibility and relative consumption rate, decreased efficiency of conversion of ingested food and digested food and relative growth rate of the four generations under elevated CO2 levels was noticed. Potential population increase index was lower for successive generations under both elevated CO, over ambient. The present findings indicated that elevated CO2 levels significantly alter the quality of castor foliage resulting in higher consumption and better assimilation by larvae, slower growth and longer time to pupation besides producing less fecund adults over generations.