Independent and interactive effects of eCO(2) and eTemp. on Spodoptera frugiperda (J E Smith) on Maize-A major input for prediction of future pest scenario

Climate change is now unequivocal and influences crops and the incidence of insect pests. Understanding the spatially variable, species-specific, and complex effects of climate change is essential in developing an appropriate pest management strategy. The two dimensions of climate change i.e., elevated temperature (eTemp.) and elevated CO2 (eCO(2)) influence insect herbivores. In the present study, the growth and development of an invasive insect pest, fall armyworm, Spodoptera frugiperda (J E Smith) (Lepidoptera: Noctuidae) on maize at eCO(2) and eTemp conditions using CO2 and temperature Gradient Chambers (CTGC) was estimated. Dilution of bio-chemical constituents was noted with lower leaf nitrogen (9%-14%), higher carbon (3%-11%), higher C : N (18%-26%), and higher tannins (13%) in maize foliage at eCO(2)+eTemp levels. A significant influence on primary parameters of insect viz., higher total consumption by larvae (38%), extended larval duration (13%) with increased larval weights (17%), and differential pupal weights (14%) in successive generations was recorded at eCO(2) + eTemp compared to ambient. Their effect was continued on various insect performance indices also, with higher relative consumption rate, RCR (40%), lower relative growth rate, RGR (11%), and varied approximate digestibility (AD), the efficiency of conversion of ingested food (ECI) and digested food (ECD) of S frugiperda larvae. The interactive effect of eCO(2) and eTemp led to a higher Potential Population Increase Index (PPII) (19%) due to higher fecund adults. The effect of eCO(2) offsets the impact of eTemp when interacting together on some of the insect parameters. The present results indicate that eCO(2) and eTemp play a key role in influencing the growth and development of S frugiperda indicating higher pest incidence in future climate change periods.