Figure 1.

Terpenoid levels (ng mg^–1 dw) and aphid numbers on Bt and non-Bt cotton as affected by prior infestation with Heliothis virescens in a glasshouse experiment. (a) Total terpenoid concentration (mean + s.e.) in the youngest and oldest true leaf of Bt and non-Bt cotton plants that were uninfested (Un) or infested (Hv) with H. virescens. (b) Numbers of Aphis gossypii per Bt and non-Bt cotton plant (mean ± s.e.) that was uninfested or infested with H. virescens. Different letters above bars indicate significant differences among treatments (p ≤ 0.05; ANOVA followed by Tukey HSD test), (a) uppercase letters, young leaves; lowercase letters, old leaves.