Evaluation of UV Protectants for Wettable Powder Formulation of Native Bacillus thuringiensis (Berliner) Isolate against Helicoverpa armigera (Hubner) in the Laboratory

Radiation severely inactivates the potency of Bacillus thuringiensis spores and crystals present in sprayed formulations leading to decreased efficacy in field. Incorporation of UV protectants to biopesticides is one of the methods to protect against radiation damage. Keeping this as objective, a native isolate BGC-1 was selected for preparation and evaluation of wettable powder formulation against second instar larvae of Helicoverpa armigera. Median lethal concentration of the BGC-1 was 1.05 g/l and assigned biopotency value was 15428.57 ITU/g. UV protectants viz., melanin, para-amino benzoic acid, polyvinyl alcohol and Congo red were evaluated by exposing formulated solution to sunlight at different intervals of time. Among four UV protectants, melanin showed an excellent UV protecting ability with the mortality of 86.67 per cent and, 116.49 μg/ml of crude protein at 5 h sunlight exposure with temperature of 43.6°C and light intensity of 4.93×10⁵ lux followed by 80.00 per cent mortality, 1.74×10⁸ CFU/ml and 109.40 μg/ml of crude protein in para-amino benzoic acid UV protectant. Next best UV protectant was congo red with the mortality of 73.33 per cent and, 90.76 μg/ml of crude protein and 1.26×10⁸ CFU/ml. It is concluded that melanin was found to be an effective UV protectant for B. thuringiensis WP formulations against H. armigera.