Fly ash-based water dispersible powder formulation of Bacillus thuringiensis var. israelensis : Development & laboratory evaluation against mosquito immatures.

Background & objectives: Bacillus thuringiensis var. israelensis (Bti) formulations are presently being used for insect control. In this study, a water dispersible powder (WDP) formulation using fly ash (FA) as a carrier material was developed and studied for its activity against the larval stages of major mosquito vector species.

Methods: An indigenous isolate Bti (Vector Control Research Centre B17) was mass produced using a 100 l fermentor in soya-based medium. The bacterial biomass was mixed with lignite FA and made into WDP formulations. The most effective formulation was used for determining 50 per cent lethal concentration (LC50 ) against the larval stages of major mosquito vector species, effect on non-target organisms and mammalian systems using standard protocols.

Results: Sixteen types of WDP formulations were prepared, of which the formulation containing bacterial biomass, FA and carboxymethyl cellulose was found to be the most effective. The LC50 values of the formulation against Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi larvae were 0.0417, 0.0462 and 0.1091 mg/l, respectively. The formulation was found to be safe to non-target organisms found associated with the mosquito larval stages and also to mammalian systems.

Interpretation & conclusions: The study shows that FA can be effectively used to replace commercially available carrier materials used in biopesticidal formulations.