Pathogenesis of entomopathogenic fungal isolates against Helicoverpa armigera

An investigation was carried out to test the pathogenicity of different entomopathogenic fungi against third instar larvae of Helicoverpa armigera at the spore load of 1 × 10⁸spores/ml of each culture under laboratory conditions. Out of four entomopathogenic fungi evaluated, isolate Nr1 of Nomuraea rileyi caused highest per cent mortality of 82.5 per cent followed by Ma2 of Metarhizium anisopliae (76.0 per cent), Bb1 of Beauveria bassiana (72.0 per cent) compared to others. Whereas, all three isolates of Verticillium lecanii used in the study, failed to cause infection. Fungal isolates, which caused highest per cent mortality (Nr1, Ma2 and Bb1) were further evaluated for LC₅₀ and LT₅₀ values at differential spore load against first to fifth larval instar. The results indicated that fungal isolates are pathogenic to early instar larvae than to later and their efficiency was proportionate to the spore concentration. The medium lethal time increased with age of larvae and decreased with increase in concentration of spores per ml for all the three fungal pathogens. However, there was no significant difference in medium lethal time between three fungal pathogens for first to third instar larvae of H. armigera. Since, N. rileyi (Nr1) recorded comparatively less LT₅₀values than B. bassiana (Bb1) and M. anisopliae (Ma2), it was concluded as a highly infective fungal agent against H. armigera.