The role of sesquiterpene lactones and phenolics in the chemical defence of the chicory plant

Amounts of the sesquiterpene lactones and the major phenolics were determined in the chicory plant at different times during the growing season. The levels of the sesquiterpene lactones (lactucin, lactupicrin and 8-deoxylactucin) and the hydroxycoumarin cichoriin were found to be highest in the most actively growing regions of the plant. In two-choice and no-choice feeding experiments with borosilicate discs, 8-deoxylactucin, lactupicrin and cichoriin significantly reduced feeding of Schistocerca gregaria at levels comparable to those present in the plant. Cichoriin was still significantly antifeedant at 0.006% dry wt, while aesculin, aesculetin and the caffeic acid ester, chicoric acid were inactive. We conclude that the three sesquiterpene lactones secreted in the latex provide a significant barrier to herbivory in chicory, although the phenolics and notably cichoriin also protect the plant from insect feeding.