Dosage-mortality Response of Gram Pod Borer, Helicoverpa Armigera (hubner) (lepidoptera: Noctuidae) to Different Geographical Isolates of Helicoverpa Armigera Nucleopolyhedrosis Virus

The relative toxicity of eight geographical isolates of Helicoverpa armigera nucleopolyhedrosis virus (HaNPV) to gram pod borer, Helicoverpa armigera (Hubner) was assessed in the laboratory. The median lethal concentration (LC50) values of different HaNPV isolates ranged from 4.3 x 10 to 1.9 x 10 PIBs/ml. Among the eight isolates, the Gulbarga (Karnataka) isolate was highly toxic, with the LC50 value of 4.3 x 10 PIBs/ml, while the Dhule (Maharashtra) isolate was least toxic (1.9 x 10 PIBs/ml). The median lethal time (LT50) for the eight isolates ranged between 117.54 to 127.69 hrs and 128.56 to 154.61 hrs at higher (1.3 x 10 PIBs/ml) and lower (2.6 x 10 PIBs/ml) concentrations, respectively. Among the tested isolates, Gulbarga isolate was faster in causing mortality of the test population with the LT50 value of 117.54 hrs and 128.56 hrs at higher and lower concentrations, respectively. Maximum time for causing mortality was noticed in Dhule isolate (127.69 hrs and 154.61 hrs). Results suggested a direct relationship between concentration of NPV and time taken (LT50) to cause mortality in H. armigera. Assessed HaNPV isolates showed considerable variability in their virulence and time taken to cause mortality. Therefore, it is critical to carefully choose suitable virulent commercial formulations of HaNPV for management of H. armigera in field.