Independent and Interactive Effects of Elevated CO2 and Temperature on Insect Pests a Major Input for Prediction of Future Pest Scenario$

Abstract

Global Mean Surface Temperature (GMST) and Global atmospheric Co2 concentrations have been increasing significantly since the last 19th century and climate change is evident in influencing agriculture. An increase in temperature and elevated Co2 (eCo2) influence crop growth significantly and affect the insect herbivores directly and indirectly. The impacts of climate change are spatially variable, species-specific, and complex, and comprehension of their impacts is vital in developing a suitable pest management strategy. The two dimensions of climate change i.e., elevated temperature (eTemp.) and elevated Co2 (eCo2) influence herbivore insect pests, and, the interactive effects of both are not studied much. At ICAR-CRIDA, several experiments were conducted to quantify the interactive effects of eCo2 and eTemp on the growth and development of several insect pests viz., Spodoptera frugiperda on maize, S. litura and Aphis craccivora on peanut, using a unique facility ‘Co2 and Temperature Gradient Chambers’, CTGC. Several feeding trials were conducted by obtaining the crop foliage from respective set conditions and the treatment associations were maintained in conducting the feeding experiments by collecting the leaves from the respective Co2 and temperature conditions. Dilution of bio-chemical constituents was noted with significantly lower leaf nitrogen (9-25%), higher carbon (3-25%), and higher relative proportion of carbon to nitrogen (18- 65%) observed in the foliage of maize and peanut crops grown under at eCo2+eTemp levels. A significant influence on primary parameters of lepidopteran insects viz., higher total consumption (TC) by larvae (15- 62 %), extended larval duration (LD) (13-25%) with increased larval weights (LW) (5-17 %) was recorded at eCo2+eTemp compared to ambient. Their effect continued on various insect performance indices also, with higher relative consumption rate, RCR (10-40%), lower relative growth rate, RGR (7-15%), the efficiency of conversion of ingested food (ECI), and digested food (ECD) of all the lepidopteran larvae. The interactive effect of eCo2 and eTemp led to a higher Potential Population Increase Index (PPII) (15-19%) due to higher fecund adults. The number of nymphs laid per Aphis craccivora adult was significantly higher and the increased mean fecundity was about 33.3 % under eCo2 than aCo2. It is noted that the effect of eCo2 offsets the impact of eTemp when interacting with some of the insect parameters. The present results indicate that eCo2t and eTemp play a key role in influencing the growth and development of the insect pests indicating higher pest incidence in future climate change periods.