Response of multiple generations of Bihar hairy caterpillar Spilosomaobliqua, feeding on castor, to elevated CO2

Abstract

The impacts of pests on crop yields in current conditions are well known, but the consequences of climate change on pests are complex. The importance of pests is significant both as important yield-reducing factors and also as early indicators of environmental changes because of their short generation times, high reproductive rates and efficient dispersal mechanisms. Any change in the growth pattern and quality of host plants can affect the survival and population dynamics of herbivores. The present study was aimed to study the host mediated impact of elevated carbon dioxide which is the major driver/factor of climate change on Bihar hairy caterpillar, Spilosoma obliqua, a polyphagous pest of economic importance, distributed throughout India mainly in Andhra Pradesh, Assam, Bihar, West Bengal, Punjab and Uttar Pradesh states. Multiple generation studies of S. obliqua were conducted at CRIDA, Entomology laboratory, Hyderabad on castor grown in Open Top Chambers (OTC’s) under two elevated CO2 conditions viz., 550 ppm and 700 ppm and were compared with ambient CO2 350 ppm (ambient). Data were recorded at regular intervals of each generation on weight of foliage consumed, larval weight, faecal matter released. Attempts have been made to quantify the efficiency with which insects exploit their food plants. In total four generations were completed on corresponding CO2 conditions. Experimental results of the studies revealed that there was a significant difference in growth and development of S. obliqua on castor. More consumption of foliage and mean larval weights were recorded across four generations under elevated condition than in ambient. Extension of larval duration was found significant across generations by one day under elevated CO2 conditions. Apart from the growth parameters, larval indices viz., approximate digestibility (AD), Efficiency of conversion of Ingested (ECI), Efficiency of conversion of digested food (ECD), Relative Consumption Rate (RCR) and Relative Growth Rate (RGR) were estimated across four generations. Increased AD and RCR with lower values of ECI, ECD and RGR were observed under elevated CO2 than in ambient. Larvae consumed more castor foliage grown under elevated CO2 and assimilated better (higher values of RCR and AD) but grew slower (lower RGR) and took longer time (one day more than ambient) to pupation.