A UNIQUE INSECTICIDAL ACTIVITY IN BACILLUS-THURINGIENSIS GROWTH-MEDIUM

The supernatant of Bacillus thuringiensis subsp. kurstaki HD-1 culture was found to be toxic against Plutella xylostella, Adoxophyes sp., Bo mbyx mori and Spodoptera litura. The activity in it against the first three species was substantially lower than that of pellets, but in S. litura activity of supernatant and pellets was similar. A small amount of 130 kDa toxin proteins was found in the concentrated supernatant a s well as in pellets by SDS-PAGE. A small amount of solubilized delta- endotoxin seemed to explain the toxicity of the supernatant against th e species except S. litura, but in S. litura the toxicity of the super natant could not be explained by its solubilized toxin protein. When e nough supernatant was given to S. litura with pellets, the insecticida l activity became higher than that of the pellets alone. These results strongly suggest that the supernatant might contain some unique facto r(s) that enhance the toxicity specific to S. litura.