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

Abstract

beta-Exotoxin (thuringiensin) was found in high titers in centrifugation supernatants and acetone/lactose powders produced from centrifugation pellets of strains Guat 1 and HD 2 of Bacillus thuringiensis (Berliner). Diets containing powders of either strain were toxic, diets containing Guat 1 supernatant were not toxic, diets containing HD 2 supernatant were slightly toxic, and diets containing powders or supernatants from uninoculated culturing medium spiked with beta-exotoxin were not toxic. Most mortality occurred within 3 d when flies fed on powders but not until 6-7 d when flies fed on HD 2 supernatant. These results indicated that the primary toxic principals of the powders were endotoxins/spores and that beta-exotoxin alone was not toxic to adult flies at the concentrations found in the supernatants or powders.