Salicin, salicin-7-sulfate, salirepin, and salirepin-7-sulfate concentrations in undamaged (control) and L. dispar caterpillar-damaged (herbivory) leaves of P. trichocarpa. Compounds were extracted with MeOH from freeze-dried plant material and analyzed using LC-MS/MS or HPLC-UV. Means and se (n = 7–8) are shown. Asterisks indicate statistical significance as assessed by Student’s t-test (**P < 0.01). Salicin (P = 0.009, t = −3.065); salicin-7-sulfate (P = 0.152, t = 1.523); salirepin (P = 0.846, t = 0.198); salirepin-7-sulfate (P = 0.588, t = 0.555). dw, dry weight; ns, not significant.