<i>In vitro</i> evaluation of microencapsulated <i>Bacillus thuringiensis</i> exposed to different temperatures against <i>Helicoverpa armigera</i> (Hubner)

Abstract

The experiment was conducted to prepare and evaluate microencapsulation of lyophilized Spore Crystal Aggregate (SCA) of native Bacillus thuringiensis isolate BGC-1 and standard isolate HD-1 against second instar larvae of Helicoverpa armigera at the Department of Agricultural Entomology, Bheemarayanagudi. The zetasizer analyzer results revealed that the microcapsule diameter ranged from 3.2 to 8.3 µm. Median lethal concentrations of the BGC-1 and Bt-HD1 were 0.66 g/l and 0.50 g/l, respectively. UV protectants viz., melanin and (PABA) para-amino benzoic acid were evaluated by exposing microencapsulated Bacillus thuringiensis to temperature regimes of 25°C, 30°C, 35°C, 40°C and 45°C in the B.O.D at different intervals of time. Among four microencapsulated formulations, BGC-1 with melanin recorded the highest mortality of 95 % at zero h exposure. As time increased, the mortality decreased and HD-1 was on par with BGC-1. HD-1 melanin showed significantly higher mortality of 62.50 to 92.50 % followed by BGC-1 (melanin) which ranged from 70 to 90 %. Even though formulations were exposed to different temperatures, because of encapsulation, potential to cause insect mortality was retained.