Lack of toxicity to adults of the Mexican fruit fly (diptera : tephritidae) of beta-exotoxin in Bacillus thuringiensis endotoxin preparations

beta-Exotoxin (thuringiensin) was found in high titers in centrifugation su pernatants and acetone / lactose powders produced from centrifugation pelle ts of strains Guat 1 and HD 2 of Bacillus thuringiensis (Berliner). Diets c ontaining powders of either strain were toxic, diets containing Guat 1 supe rnatant were not toxic, diets containing I-ID 2 supernatant were slightly t oxic, and diets containing powders or supernatants from uninoculated cultur ing medium spiked with beta-exotoxin were not toxic. Most mortality occurre d within 3 d when flies fed on powders but not until 6-7 d when flies fed o n HD 2 supernatant. These results indicated that the primary toxic principa ls of the powders were endotoxins/spores and that beta-exotoxin alone was n ot toxic to adult flies at the concentrations found in the supernatants or powders.