Potentiation of Bacillus thuringiensis var. kurstaki with Thuringiensin on Beet Armyworm (Lepidoptera: Noctuidae)

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Abstract
Toxicity of several formulations of Bacillus thuringiensis var. kurstaki (Berliner) (BTK) to beet armyworm, Spodoptera exigua (Hübner), was determined using neonate larvae in a diet incorporation bioassay. LC50’s for formulations of the spore/crystal complex of two BTK isolates, Dipel 2X and Javelin, were 299 μg/ml and 81.2 μg/ml of diet, respectively. The LC50 of ABG-6162, an experimental formulation of thuringiensin, was 37.5 μg (AI)/ml of diet. Time of death varied with treatment. With Dipel 2X or Javelin, most mortality (52%) occurred by day 3, whereas with ABG-6162, mortality was greatest (52%) between days 5 and 6. Combinations of thuringiensin and BTK resulted in potentiation, whereas combinations of the two BTK formulations produced an additive effect. Combinations of BTK and thuringiensin increased rate of mortality, with 90% of the total mortality occurring within 3 days.