In vivo Enhancement of Nucleopolyhedrovirus Infection in Helicoverpa armigera (Hübner) by the Granulovirus of Spodoptera litura Fabricius

Abstract

Biopesticides based on baculoviruses offer great scope as promising viral insecticides against Helicoverpa armigera (Hübner). However, an important limitation in the use of baculoviruses is their reduced efficacy against grown up larvae. The infectivity of NPV against grown up larvae were reported to be enhanced by the presence of a viral enhancing factor (VEF) in granuloviruses (GV). Hence, we investigated the possible interaction of GVs of Spodoptera litura (SlGV), Agrotis segetum (AsGV), Plutella xylostella (PxGV), Achaea janata (AjGV) and Chilo infuscatellus (CiGV) separately with the NPV of H. armigera (HearNPV) against second, third, fourth and fifth instar H. armigera. Of the GVs tested with HearNPV, SlGV alone synergized HearNPV action with reduced LC₅₀ values. The integration of SlGV with HearNPV resulted in 9.38, 10.93, 10.70 and 13.32 fold reduction in LC₅₀ values against the second, third, fourth and fifth instars respectively. Tests conducted with heat inactivated (at 75, 80, 85 and 121°C for 10 min) and heat shielded SlGV could give similar effects with HearNPV indicating that the cause for the virulence enhancement rests with the capsular protein and not the virions of the SlGV, since the virions could be inactivated at temperatures more than 70°C. Integration of SlGV and HearNPV was found to shorten the LT₅₀ values.