Effect of temperature on pathogenicity of Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin against Spilosoma obliqua (Walker)

Pathogenicity of Beauveria bassiana to Spilosoma obliqua larvae was higher at low temperature (20°C) compared to higher temperature (30°C). The LC₅₀ values of B. bassiana at 20 and 30°C were 8.63 and 17.8x 10⁶ conidia ml⁻¹ against second instar larvae, 16.4 and 62.3x10⁶ against third instar, and 33.7 and 70.2 x 10⁶ conidia ml⁻¹ against fourth instar, respectively. The LT₅₀ values at 20°C temperature were 155.4, 159.0 and 162.9 hours to second, third and fourth instar larvae, respectively, compared to 167.6, 168.9 and 169.8 hours, respectively, at 30°C temperature. The LC₅₀ values of Metarhizium anisopliae against S. obliqua at 20°C temperature was 54.1, 66.2 and 73.8 x 10⁶ conidia ml⁻¹ against second, third and fourth instar larvae, respectively, which was 1.58, 1.14 and 1.08 fold lower than values obtained at 30°C temperature, i.e., 58.7, 75.1 and 80.1x10⁶ conidia ml⁻¹, respectively. Similarly, the LT₅₀ values at 20°C were 161.3, 162.9 and 169.5 hours against second, third and fourth instar larvae, respectively, which were 1.08, 1.08 and 1.05 fold lower than LT₅₀ obtained at 30°C temperature, respectively.