Influence of varying temperatures on toxicity of biorationals against diamondback moth, Plutella xylostella L.

Abstract

Effect of various temperatures on the efficacy of five biorationals, viz. Beauveria bassiana (1.15% WP), Metarhizium anisopliae (1.15% WP), Bacillus thuringiensis (0.5% WP), Azadirachtin (300 ppm) and Spinosad (45 SC) in terms of median lethal concentration (LC₅₀) value was evaluated against diamondback moth, Plutella xylostella larvae. The toxicity data for biorationals against P. xylostella on the basis of larval mortality revealed that M. anisopliae (1.15% WP), B. thuringiensis (0.5% WP), Azadirachtin (300 ppm) and Spinosad (45 SC) registered higher effectiveness (lower LC₅₀ value) at 25°C whereas, increase in temperature led to declined efficacy of biorationals; whereas, use of entomopathogenic fungi, B. bassiana (1.15% WP) was most effective at 30°C and revealed lower effectiveness (higher LC₅₀ value) at 25° and 35° C temperatures. Data on the influence of temperature on toxicity of biorationals to P. xylostella on the basis of adult emergence revealed lowest LC50 value for B. thuringiensis (0.5% WP) at 25°C and the efficacy decreased with increase in the temperature, whereas, M. anisopliae (1.15% WP), B. bassiana (1.15% WP), Azadirachtin (300 ppm) and Spinosad (45 SC) were most effective at 30°C and the higher LC₅₀ value were evident at temperature above 30°C, indicating the reduced efficacy of biorationals with increase in temperature beyond 30°C or preference for lower temperature regimes under laboratory conditions.