Comparative evaluation of temperate, subtropical, and tropical isolates of nucleopolyhedrovirus against tomato fruit borer, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae)

Abstract

Background The tomato fruit borer, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), is a serious insect pest owing to its polyphagous nature, migrating long distances, greater capacity to develop resistance against insecticides and persistence in cropping areas. The comparative evaluation of temperate, sub-tropical and tropical H. armigera NPV (HearNPV) isolates was carried out to determine the potential of local and exotic HearNPV isolates for the management of H. armigera in Kashmir, India, having a temperate climate. Results Mortality of 2nd instar H. armigera larvae with three different HearNPV isolates at different concentrations ranged between 13.40 and 73.25%, with significant differences between the concentrations in each isolate under laboratory conditions. The median lethal concentration (LC50) values of HearNPV-IND-K, HearNPV-IND-J, and HearNPV-IND-B isolates against 2nd instar H. armigera larvae were 4.62 × 103, 5.99 × 104, and 7.24 × 104 OBs/larva at 10th day post inoculation, with significant differences among the isolates. In time response bioassays, the cumulative mortality (%) caused by median lethal concentration (LC50) of HearNPV-IND-K, HearNPV-IND-J and HearNPV-IND-B isolates over a period of 10 days was 50.33, 49.00 and 49.00%, respectively. Their median survival time (ST50) values against 2nd instar H. armigera larvae were 8.10, 8.94 and 9.50 days, respectively, with significant differences among the isolates. The results revealed that the LC50 and ST50 values of HearNPV-IND K isolate were significantly lower than HearNPV-IND-J and HearNPV-IND-B isolates. The cumulative mortality of H. armigera larvae with HearNPV-IND-K, HearNPV-IND-J and HearNPV-IND-B isolates at different concentrations ranged between 22.00–68.32, 20.54–55.17, 11.66–44.33%, respectively, on tomato crop under field conditions. The highest mortality rate of 68.32% was observed at the local isolate (HearNPV-IND-K). Conclusions It’s concluded that the local isolate had the potential for the development of species-specific and environmentally safe biocontrol agent for organic farming and its incorporation into Integrated Pest Management program may reduce the use of chemical insecticides in Kashmir.