Specificity of phenolic glycoside induction in willow seedlings (Salix sericea) in response to herbivory

Salix sericea (Marsh.) (Salicaceae) seedlings were used to investigate phytochemical induction of phenolic glycosides following beetle herbivory. Seven-week-old full-sibling seedlings were subjected to one of three damage treatments: Plagiodera versicolora adults, P. versicolora larvae, or Calligrapha multipunctata bigsbyana adults. Salicylate concentrations were measured locally (within damaged leaves) and systemically (above and below damaged leaves) 4 d later. Herbivory caused differential salicylate induction; 2'-cinnamoylsalicortin was induced, whereas salicortin was not. The induction of 2'-cinnamoylsalicortin was not specific with regard to the species or developmental stage of beetle tested but did vary with leaf age: induction occurred in the younger undamaged leaves but not in the damaged leaves or in the older undamaged leaves. The amount of leaf area consumed had no detectable effect on induction, indicating an all-or-none response triggered by even small amounts of herbivory. Locally, herbivory caused a decrease in salicortin concentrations, probably because of degradation within the damaged leaves. These results suggest a specific but generalized induced response to these leaf-feeding beetles.