1985 Fall Armyworm Symposium: Biological Control: Interactions Between Bacillus Thuringiensis and its Beta-Exotoxin in Fall Armyworm (Lepidoptera: Noctuidae) Neonate Larvae

Wayne A. Gardner, Andrew F. Pendley, Greggory K. Storey


Interactions between Bacillus thuringiensis Berliner and its beta-exotoxin, thuringiensin, were evaluated in neonate larvae of Spodoptera frugiperda (J. E. Smith). The median lethal concentration of B. thuringiensis (Dipel) was 113.8 ug/ml of diet. Test larvae were continuously fed on diet incorporated with one-half of this concentration (56.9 ug/ml) in combination with various concentrations of the exotoxin. Potentiation was the prevalent type of interaction observed between 2 and 10 days after initial exposure. Treatments with B. thuringiensis in combination with 1, 15, 20, and 100 ppm of exotoxin yielded higher mortality levels and lower median lethal times than treatments with the individual agents alone. The combination of B. thuringiensis with 10 ppm of exotoxin was additive after 3 days postexposure. Antagonism occurred in combinations of B. thuringiensis with 1 and 10 ppm of exotoxin prior to 7 and 4 dy postexposure, respectively. This might be attributed to a previously-observed feeding deterrent factor in the beta-exotoxin.

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