Pathogenesis of entomopathogenic fungal isolates against Helicoverpa armigera

摘要

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 x 10~8 spores/ml of each culture under laboratory conditions. Out of four entomopathogenic fungi evaluated, isolate Nrl of Nomuraea rileyi caused highest per cent mortality of 82.5 per cent followed by Ma.2 of Metarhizium anisopliae (76.0 per cent), Bbl of Beauveria bassiana (72.0per 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 (Nrl, Ma2 and Bb1) were further evaluated for LC_(50) and _(50)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 increasein 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 LT_(50)values than B. bassiana (Bbl) and M. anisopliae (Ma2), it was concluded as a highly infective fungal agent against H. armigera.