Comparative Efficacy of UV Screens in Protecting the Activity of a Bacillus thuringiensis formulation

UV inactivation of Bacillus thuringiensis var. israelensis (B. t. i.) toxin is a common problem encountered with any floating formulation against mosquito larvae. An alginate encapsulated, slow-release, floating formulation of B. t. i., incorporated with UV screens such as acriflavin or methyl green or congo red was prepared and evaluated for larvicidal activity against Culex quinquefasciatus. The data indicated: i. Encapsulation of B. t. i. toxin in sodium alginate has prolonged its residual activity for 45 days, ii. all the UV screens used gave significant level (F=21.66, df = 3716, P<0.0001) of protection to B. t. i. toxin from inactivation by sunlight even after 180 h exposure to direct sunlight (4 hours exposed to direct sunlight daily till 45th day) and iii. compared to acriflavin or methyl green, congo red provided excellent protection.