Bacillus thuringiensis (Bt) is currently the most commonly used microbial pesticide. In the previous study, Bt IMBL-B9 known for its high toxicity against Spodoptera exigua, S. frugiperda and Plutella xylostella was characterized. To develop novel biopesticide, optimization of culture medium is required for the cost-effective mass production for toxin production of IMBL-B9. Through experimental design by Plackett-Burman design, ingredients that significantly influenced the production of IMBL-B9's toxin were selected. Using these results, the novel culture medium for IMBL-B9 was developed and the toxin yield of IMBL-B9 was significantly increased than conventional media by using this medium. These results could be useful for the development of biopesticides.

The beet armyworm, Spodoptera exigua, is one of the worldwide distributed agricultural pest insects and has been known to show high resistance to conventional chemical insecticides. Since it has been reported that secondary metabolites from actinomycetes show insecticidal activities against various insect pests, actinomycetes could be a potential source of insecticidal compounds. In this study, culture extracts of Streptomyces strains were tested for their insecticidal activity against Spodoptera exigua. Among them, culture extracts of IMBL-0003 strain which was identified as Streptomyces celluloflavus showed a high insecticidal activity (more than 90% mortality). These results suggested that secondary metabolites of this isolate could have potentials to be a efficient eco-friendly pesticide for controling Spodoptera exigua.