Tobacco budworm, Heliothis virescens (Lepidoptera : Noctuidae): Larval location and mortality on Bacillus thuringiensis-treated cotton

One-d-old Heliothis virescens (F.) larvae were placed on Bacillus thuringie nsis var. kurstaki Berliner-treated cotton leaves and terminals in the labo ratory. Larval movement, food consumption and mortality were examined at 3, 6, 12, 24 and 48 h. Untreated leaves had a greater percentage of larvae on their under side than on their upper side; this location was not influence d by treatment with B. thuringiensis. When B. thuringiensis was applied to cotton terminals, first instars moved from B. thuringiensis-treated meriste ms; this movement increased with an increase in rate. Bacillus thuringiensi s treatment also resulted in increased movement of larvae from the leaves a nd terminals onto the inner cup surface, although this movement was signifi cantly greater than the untreated control only during the first 12 h after treatment. The leaf area consumed decreased with an increase in B. thuringi ensis rate, but was not significantly correlated with larval mortality.