Interactive effects of temperature and CO2 on efficacy of insecticides against Spodoptera litura Fab. in a global warming context.

Abstract

Influence of two dimensions of climate change i.e., elevated temperature (eTemp) and elevated CO2 (eCO2) on toxicity of insecticides against Spodoptera litura Fab. on peanut using CO2 Temperature Gradient Chambers (CTGC) facility was investigated. The insecticides viz., diamides (flubendiamide), avermectins (emamectin benzoate), organophosphates (quinalphos), spinosyns (spinosad) and synthetic pyrethroids (deltamethrin) were tested for their efficacy and persistence toxicity (PT) at eTemp and eCO2. The twelve set conditions comprising of reference (28 ± 0.5 °C; 380 ppm), eTemp (29, 30, 31, 32, 34 ± 0.5 oC with 380 ppm CO2), eCO2 (28 ± 0.5 oC; 550 ppm) and eTemp+eCO2 (29, 30, 31, 32, 34 ± 0.5 oc with 550 ppm CO2) were maintained in CTGC. Interactive effects of eCO2 and eTemp caused the higher LC50 values of spinosad and deltamethrin with negative temperature coefficients and showed the ‘reduction of toxicity’. Lower LC50 values and positive temperature coefficients for flubendiamide (6.67), emamectin benzoate (7.38) and quinalphos (3.04) were recorded, indicating the ‘higher toxicity’ at interactive eCO2 and eTemp. The order in PT of insecticides was deltamethrin<quinalphos<flubendiamide< emamectin benzoate< spinosad and these insecticides persisted for shorter period at eTemp + eCO2 conditions over reference. Present results indicate the negative impact of eTemp and eCO2 on efficacy of spinosad and deltamethrin necessitating their higher requirement than was needed to achieve equal control at reference/ambient temperature and CO2.