Stability and controlled release properties of carboxymethylcellulose-encapsulated Bacillus thuringiensis var. Israelensis

The mosquito and blackfly pathogen, Bacillus thuringiensis Berl. var. israelensis (B.t.i.). containing spores and toxin crystal, was successfully encapsulated in an insolubilized carboxymethylcellulose (CMC)‐aluminum matrix creating a controlled‐release bead formulation. The release rate of B.t.i. from this formulation was sufficient to kill Culex sp. larvae during bioassays performed in the laboratory. The CMC concentration significantly affected the release rate of the bacterium. All types of beads tested exhibited a high initial release of B.t.i. in the first week of experiments, followed by a slower rate later. Levels of 10 g kg−1 CMC solution and 0–05 m aluminium sulfate were found to be optimal in the formulation mixture for polysaccharide and gellant, respectively. This type of bead gave the fastest release of the bacterium and caused 100% larval mortality as from the second day of treatment. While acidic pH, high temperature and UV exposure drastically decreased spore viability of B.t.i., the CMC‐encapsulated formulation was more stable to these conditions. Larvicidal activity of encapsulated B.t.i. was more resistant to high temperature (50°C) than the unformulated B.t.i. The high response of Culex larvae to the encapsulated B.t.i. suggests that the formulation could be employed effectively in the field.