Encapsulation of Bacillus thuringiensis using sodium alginate and chitosan coacervates for insect-pest management

The study investigates the complex coacervation process of sodium alginate (SA) and chitosan (CS), aiming to optimize the yield of coacervates formed from these marine polysaccharides. Structural interactions between SA and CS were analyzed across varying chitosan concentrations (0.01 mg to 20 mg/mL) using turbidimetric analysis. The optimal chitosan concentration for maximum coacervate formation was determined to be 10 mg/mL. Under these conditions, Bacillus thuringiensis var. kurstaki (Bt) strain Bt-127 was successfully microencapsulated, achieving an entrapment rate of 56 %. Boric acid was selected as the cross-linking agent due to its compatibility with Bt and the SA-CS coacervates. Microscopic analysis confirmed the formation of coacervates/microcapsules and effective entrapment of Bt within them, with an entrapment efficiency of 98 %. Fourier transform infrared spectroscopy verified the chemical interactions between SA and CS within the coacervates. Bioassays against Spodoptera litura larvae using the leaf dip method demonstrated the efficacy of the encapsulated Bt formulation, showing an LC₅₀ of 0.51 g/L. These findings highlight the potential of SA-CS coacervates for effective Bt microencapsulation and application in pest control.