(Molecular and biological characteristics of some geographic isolates of nucleopolyhedrovirus of Helicoverpa armigera (Lep.: Noctuldae

Seven geographic isolates of Helicoverpa armigera NPV were characterized by PCR-RFLP techniques and their comparative virulence to second instar larvae of H. armigera (Hübner) were compared before and after exposure to simulated sunlight as well as open weather conditions on cotton and tomato plants. The PCR products of 25K FP region showed no difference among the isolates (780 bp). The PCR amplification products revealed genetic diversity among the 7 HearNPV isolates when they were digested individually using four different restriction enzymes (HindIII, BamHI, PstI, and EcoRI). The bioassays of the HearNPV isolates against the second instar larvae of H. armigera, before and after exposure to simulated sunlight, revealed a range of variation in their biological activity. However, the NGM isolate was the most virulent with the lowest LC50 and LT50 values. The dose-inhibitory response of the second instar larvae of H. armigera to the virus isolates revealed NGM isolate to be the least susceptible to simulated sunlight, having the highest ID50 value (462.9 W/m2). Experiments on persistence of HearNPV isolates on cotton and tomato plants under open weather conditions showed that the persistence of the viral isolates was relatively higher on tomato than on cotton.