Preliminarylab studies on the use of Beauveria bassiana (Balsamo) Vuillemin against Callosobruchus chinensis (Fabricius) (Coleoptera: Bruchidae) under different temperature and relative humidity regimes

Abstract

Laboratory experiments were carried out in order to assess the insecticidal effect of Beauveria bassiana (Balsamo) Vuillemin against Callosobruchus chinensis (Coleoptera: Curculionidae). Two fungal preparations viz., a conidia and a conidial suspension were compared, dry conidial bioassays were carried out on 250 g of greengram, in glass jars maintained at 28±2°C, and 70% RH. At higher doses (3.5x108 conidia/g), B. bassiana isolate-1 produced a higher percentage of mortality up to 82.00 percent whereas, Bb-2 recorded 72.50 percent mortality at 2.25x108 conidia/g at 10 DAT. Immersion with conidial suspension bioassays were carried out, at higher concentrations of Bb-1 i.e, 2 x 108 and 2 x 107 recorded 86.67 percent mortality at 10 DAT. At the same concentration level Bb-2 recorded 80.00 percent mortality. In all the experiments, mortality increased with increase in dose rates and exposure time. Bb-1 showed lowest LC50 value i.e., 1.347x108 conidia/g at 9 DAT. Bb-1 performed well when compared to Bb-2. Bioassay with standardised dose of fungus has been carried out with different temperature and relative humidity regimes viz., 20, 25, 30 and 35 °C and four relative humidity (RH) levels, 30, 50, 70 and 90%. The organoleptic study magnificently demonstrate that there was no significant difference between green gram when treated with entomopathogen regarding all organoleptic characteristics after twelve months of storage. For commercial purposes the application of admixtures of dry conidia of entomopathogenic fungi in food grains is advised. The results of the present work suggest that, B. bassiana can be used to manage C. chinensis in storage.