Imidacloprid efficacy against brown planthopper, Nilaparvata lugens under elevated carbon dioxide and temperature

Abstract

Influence of elevated CO2 and temperature (elevated condition (EC)) vis-à-vis ambient CO2 and tempera-ture (ambient condition (AC)) on plant (rice) growth, insect Nilaparvata lugens (brown planthopper (BPH)) population and insecticide (Imidacloprid) efficacy was evaluated under open top chamber conditions. EC had a positive effect on rice crop through increase in tillers numbers (18.4%), reproductive tillers (20.5%) but in-flicted negative effect on 1000-grain weight (11.7%) and grain yield (11.9%). Likewise, higher canopy cover of the plant was noticed under EC (16.1 cm) when compared to AC (12.9 cm). With respect to BPH population during 2013 and 2014, EC exhibited posi-tive effect by enhancing its mean population to 66.1 and 49.4 hoppers hill–1 respectively, compared to cor-responding 36.8 and 29.5 hoppers hill–1 under AC. With respect to Imidacloprid efficacy against BPH, LC50 was significantly lower under EC (0.044%) in comparison to AC (0.065). Similarly, in 2013 under AC, 500, 600, 700 l ha–1 spray volume caused >50% BPH mortality than 400 l ha–1 at 5 day after spray. However, during the same exposure period under EC, only 700 and 600 l ha–1 produced more than 50% mortality compared to 500 and 400 l ha–1. Positive in-fluence of EC on BPH population resulted in signifi-cantly higher yield loss (41.1%) compared to ambient (26.5%) in untreated check. Though LC50 under EC was less, higher canopy size and more BPH population resulted in increase in spray volume to cause similar mortality as of AC. The present results indicated that spray volumes of 400 and 500 l ha–1 was found insuffi-cient to manage BPH population under EC; hence the current management strategies for BPH needs to be redefined under changing climatic conditions.