Effect of Supplementation of Medium with Larval Extract on the Virulence of Beauveria bassiana (Balsamo) Vuillemin against Spilosoma obliqua Walker

Bioassays were conducted with two isolates of Beauveria bassiana (Balsamo) Vuillimen, cultured on Sabouraud's dextrose agar (SDA) medium supplemented with host insect larval extract against Spilosoma obliqua (Walker) larvae. The LC₅₀ values of isolate MTCC 984 and MUCL 32508, grown on SDA medium, were 1.43 and 7.69×10⁶ conidia ml^-1, 2.34 and 11.6×10⁶ conidia ml^-1, and 3.53 and 19.5×10⁶ conidia ml^-1 against second, third and fourth instar larvae, respectively. However, the virulence of both isolates increased when grown on SDA medium supplemented with larval extract. The LC₅₀ values of isolates MTCC 984 and MUCL 32508 grown on SDA medium supplemented with larval extract were 0.86 and 3.31×10⁶ conidia ml^-1, 1.95 and 6.28×10⁶ conidia ml^-1, and 2.38 and 14.6×10⁶ conidia ml^-1 against second, third and fourth instar larvae, respectively, showing thereby higher virulence of the former in terms of LC₅₀ and LT₅₀ value against S. obliqua larvae.