Effect of Growth Media on the Bioefficacy of Bacillus thuringiensis Berliner, against Spodoptera lifura (Fabricius)

The investigation on the effect of four growth media (nutrient agar medium, starch medium, King's B medium and malt extract peptone dextrose agar medium) on the growth of Bacillus thuringiensis Ber. (B.t.) from three commercial formulations viz., Dipel 8L, Delfin WG and Halt WP and it's bioefficacy thereafter as pure culture against Spodoptera litura Fab. was conducted under laboratory conditions. The results revealed that Dipel 8L showed superior growth with 8.5 x 10⁹ cells ml⁻¹ followed by Delfin WG with 5.5 x 10⁹ cells ml¹ and Halt WP with 1.8 x 10⁹ cells ml⁻¹ on nutrient agar medium. The harvested B.t. cells (pure cultures) when tested against 3rd instar larvae of S. litura, indicated that Delfin WG grown on nutrient agar medium recorded lowest EC₅₀ (1.8 x 10⁵ cells ml⁻¹) value compared to the values (2.9 x 10⁵ to 9.7 x 10⁵ cells ml⁻¹) of other pure cultures. The same treatment was superior in resulting higher feeding inhibition (34.26%), reduction in larval (22.69%) and pupal (28.01%) weight, and pupal (7.22%) and adult (4.72%) malformations over control.