Unravelling the impacts of elevated CO2 and elevated temperature on Spodoptera exigua in chickpea - Indian climate change context

Abstract

Climate change is a worldwide concern with a peril to the long-term viability of agriculture. Elevated temperature (eTemp.) and elevated CO₂ (eCO₂) are the two facets of climate change with a substantial effect on crop production and protection. The life table analysis of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) in chickpea was conducted using a unique facility, CO₂ and Temperature Gradient Chambers (CTGC). Two CO₂ levels (aCO₂ – 400 and eCO_2- 550 ppm) and six temperatures (20, 27, 28, 30, 33 & 35 ± 0.5 °C) were adopted for the experimentation. Leaves of the chickpea crop raised at eCO₂ had higher carbon, lower leaf nitrogen, and a higher ratio of carbon to nitrogen (C: N) over aCO₂. Higher r_m, intrinsic rate of increase (0.22), Ro, net reproductive rate (123.80) and λ, finite rate of increase (1.25) were with eTemp + eCO₂ condition and started decreasing beyond the point of inflection that varied with the parameters. Reduction in generation time ‘T’ with increase in temperature at both levels of CO₂ and varied between 50 and 20 days at 20–35 °C. Empirical models developed using the data of life table parameters with eTemp and eCO₂. Ensembled temperature data of 32 GCMS of 4 Representative Concentration Pathways (RCPs) viz., RCP 2.6, 4.5, 6.0 and 8.5 of Coupled Model Inter comparison Project 5 (CMIP5) models was used for predicting the pest scenarios. The increase in projected maximum temperature (Tmax) is 0.71–4.66 °C and minimum temperature (Tmin) is 0.82–5.26 °C which are apparent in 3 future Time slice periods (TSPs) viz., 2030's, 2050's and 2080's over base line (BL) period across 4 RCPs at 18 chickpea growing locations of India. The prediction of S. exigua during the future TSPs reveals that insect pest would be with higher ‘r_m’ and ‘λ’, varied ‘R_o’ and reduced ‘T’ at 18 locations of India implying increased pest prevalence in the future.