Efficacy of Microbials Alone and in Combinations on Larval Mortality of Helicoverpa armigera (Hüb.)

Three different microbials, Bacillus thuringiensis var. kurstaki (Btk, Dipel 8L), Saccharopolyspora spinosa (Spinosad 45 SC, Tracer) and Beauveria bassiana (pure culture developed from Biopower) were tested alone and in combinations at their pre-determined LC₅₀S and LC₂₅S against the third instar larvae of Helicoverpa armigera. The individual treatments of S. spinosa (0.0018 or 0.003%) and its combinations (0.006 or 0.0013%) with Btk (0.02 to 0.08%) resulted in significantly higher larval mortalities of 100% and 64.8 to 110.0% respectively. The individual treatment of Btk (0.05 to 0.19%) and B. bassiana (1.6 x 10⁵ to 2.5 x 10⁵, spores/ml) were at par resulting in 53.0 to 75.6 and 60.4 to 75.3% larval mortality, respectively. The combined treatments of the microbial agents at their LC₂₅ resulted in additive lethal effect in most of the combinations.