Optimizing suspensibility, stability and virulence of commercial products of Bacillus thuringiensis

The purpose of this study was to determine the effect of some additives on stability and suspensibility of wettable powder (WP) formulation of Bacillus thuringiensis (Bt) in laboratory products (optimized formulation) and commercial formulations. For preparation of optimized formulation; sucrose, lactose, sodium alginate, coconut fiber and aluminum silicate were added to the dried powder of bacterial product in two different treatments; which were different in aluminum silicate (optimized formulation 1) and coconut fiber (optimized formulation 2). The efficacy and toxicity of wettable powders were tested on diamondback moth, Plutella xylostella (L.) (Lep.: Plutellidae) larvae. The results of various tests for stability showed that the additives had positive effects on the storage life of the optimized formulation. The suspensibility of the optimized formulations (70%) was significantly higher than those of the commercial formulations. Our results showed that adding sucrose in both commercial products caused an increase in toxicity (lower LC50s), whereas, the suspensibility parameter varied depending on the type and feature of the products. In conclusion, selecting low-cost and available additives would improve the physical and biological characteristics of Bt formulations, which has a significant effect on the development and application of biopesticides.