Bacillus thuringiensis and nuclear polyhedrosis virus for the enhanced bio-control of Helicoverpa armigera

Abstract

A number of entomopathogenic microbial agents infect a wide array of insects and cause epizootics from time to time. Bacillus thuringiensis (Bt) and Nuclearpolyhedrosis virus (NPV) are two important potential pathogens of Helicoverpa armigera. Investigations were carried out on integration of B. thuringiensis and Nuclearpolyhedrosis virus to determine its impact on survival of second and fourth instar larvae under laboratory conditions. Both Bt and NPV were applied using diet incorporation method. Larvae continued to feed for 48 h when a batch of fifteen insects was exposed to diet mixed with any of the treatment. Mortality was recorded every 48 h until larvae died or pupated. The susceptibility of H. armigera larvae decreased with older stage as greater mortality was recorded in second instar larvae (95.45%) in comparison to fourth instar larvae (82.48%) in combined application of Bt and NPV. Application rate of Bt was the key for type of interaction as only one synergistic interaction (CTF≥20) was recorded when lower dose of Bt was combined with NPV, rest of the combinations were additive and independent (CTF≥20). Reduction in the pupation, adult emergence and egg eclosion was found directly related to pathogenicity of the applied agents. This study would be helpful to extend the integrated use of pathogens under field condition to many important insect pests.