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

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.