Effect of Natural Sunlight on the Activity of Different Geographic Isolates of Nucleopolyhedrovirus of Helicoverpa armigera (Hubner)

Abstract

Susceptibility of seven geographic isolates of Helicoverpa armigera NPV to sunlight was evaluated by subjecting them to different exposure times (0, 3, 6. 12, 24 and 36 hours). The viral dose of exposure was 1 í— 10⁷ POB/ml and bioassays were performed at a dose of l í— 10⁵ POB/ml of each virus isolate. The study showed that exposure to natural sunlight affected the activity of the different HearNPV isolates. About six hours of exposure reduced the activity of the viral isolates by nearly 50 percent. By 36 hours, all the isolates had lost their activity by about 70 percent. There were no significant differences in the susceptibility of different isolates to natural sunlight. However, NGM isolate showed the lowest inactivation after 36 hours of exposure. Time-mortality response of HearNPV isolates indicated that exposure to natural sunlight beyond 12 hours declined the viral activity to the extent of 50 percent. The order of IT₅₀ values for the isolates was Negamum > Ooty > Coimbature > Mumbai > Parbhani > Hyderabad > Rahuri.