Effects of Bacillus thuringiensis isolates and single nuclear polyhedrosis virus in combination and alone on Helicoverpa armigera

Abstract

Cotton bollworm is a key pest of cotton and other crops in many parts of Asia. Evaluation of three native Bacillus thuringiensis isolates and HaSNPV on cotton bollworm was studied. Results revealed that KD-2 isolate was the superior isolate, that its LC50 was 1.2 × 107 spore ml−1 and LC50 of HaSNPV equal to 9.2 × 103 OB ml−1. Interactions on the mortality and debilitating effects between B. thuringiensis KD-2 isolate (3 × 106, 6 × 106, 1.21 × 107 and 1.8 × 107 spore ml−1) and HaSNPV (2.3 × 103, 4.6 × 103 and 9.2 × 103 OB ml−1) on second instars larvae of Helicoverpa armigera were evaluated in laboratory. The larvae of cotton bollworm were fed for 48 h on the treated diets. The results revealed that the Bt at 1.2 × 107 spore ml−1, mixed with all above-mentioned concentrations of HaSNPV, had antagonistic effects. However, the Bt at 1.8 × 107 spore ml−1, mixed with HaSNPV at 9.2 × 103 OB ml−1, had additive effect. The Bt at 6 × 106 spore ml−1 mixed with all above-mentioned concentrations of HaSNPV demonstrated additive effects. The Bt at 3 × 106 spore ml−1 had additive effect with HaNPV at 2.3 × 103 and 4.6 × 103 OB ml−1. The mortality observed in larvae infected with the combination of both Bt (3 × 106 spore ml−1) and HaSNPV (9.2 × 103 OB ml−1) was interpreted as synergist effect. Therefore, it could be concluded that combination of the lowest Bt concentration and the highest HaSNPV concentration had synergist effect on H. armigera second instar larvae.