ABSTRACT
A laboratory bioassay method was developed to determine the toxicity of Bacillus thuringiensis var. kurstaki to larvae of the tobacco budworm, Heliothis virescens (F.). A soybean fiber based diet was mixed with water containing B.t. and neonate larvae were placed on the diet. Toxicity was determined 4-5 days later. The procedure gave a useful method for assaying the toxicity of B.t.. In other tests, it was demonstrated that tobacco budworm larvae which had survived exposure to B.t. were more susceptible to discriminating doses of the insecticides chlorpyrifos, thiodicarb and cypermethrin than unexposed insects. The data suggest that combinations of B.t. and low doses of insecticides may be useful in managing field populations of the tobacco budworm.
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