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 × 10⁷spore 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 × 10⁷spore 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 × 10⁶spore 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 × 10⁶spore 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.

Keywords:

• Bacillus thuringiensis
• cotton bollworm
• interaction
• single nuclear polyhedrosis virus

Acknowledgements

This research was carried out in the BioControl Department, Iranian Research Institute of Plant Protection, Tehran, Iran. The authors thank Dr David Mota-Sanchez for helpful comments and revision of the manuscript.