Encapsulation of Bacillus thuringiensis in an inverse Pickering emulsion for pest control applications

Here, we present an inverse Pickering emulsion-based formulation for Bacillus thuringiensis serovar aizawai (BtA) encapsulations utilized towards pest control applications. The emulsification was carried out by high shear homogenization process via ULTRA-TURRAX®. The water-in-mineral oil emulsions were stabilized by commercial hydrophobic silica. Different silica contents and water/oil ratios were studied. Stable emulsions were obtained at 2 and 3 wt% silica at 30% and 20% water volumes, respectively. The structure of the Pickering emulsions were characterized by laser scanning confocal microscopy and cryogenic scanning electron microscopy. The BtA cells, spores and crystals were encapsulated in the water droplets of the inverse Pickering emulsions. An emulsion composed of 3 wt% silica and 30% water was found to be the most suitable for encapsulation. The pest control efficiency of the encapsulated BtA against Spodoptera littoralis first instar larvae was tested. The studied BtA/emulsion system exhibited a mortality rate of 92%. However, the non-formulated BtA has shown 71% mortality, and the emulsion alone resulted in only 9% mortality. These findings confirm that an emulsion with encapsulated BtA can function as an efficient formulation for biopesticides.