Tobacco Budworm, Heliothis virescens (Lepidoptera: Noctuidae): Larval Location and Mortality on Bacillus thuringiensis-Treated Cotton

Abstract

One-d-old Heliothis virescens (F.) larvae were placed on Bacillus thuringiensis var. kurstaki Berliner-treated cotton leaves and terminals in the laboratory. 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 influenced by treatment with B. thuringiensis. When B. thuringiensis was applied to cotton terminals, first instars moved from B. thuringiensis-treated meristems; this movement increased with an increase in rate. Bacillus thuringiensis treatment also resulted in increased movement of larvae from the leaves and terminals onto the inner cup surface, although this movement was significantly greater than the untreated control only during the first 12 h after treatment. The leaf area consumed decreased with an increase in B. thuringiensis rate, but was not significantly correlated with larval mortality.