Differences in insect feeding patterns and effect on volatile emission. A. Pictures of the characteristic feeding damage caused by second instar Lymantria dispar, fifth instar L. dispar and fifth instar Laothoe populi on Populus nigra leaves. B. Correlation between two insect feeding parameters (number of leaves damaged and number of lesions) and total volatile emission of P. nigra leaves (combined emission of the 20 compounds investigated) in relation to the amount of leaf area eaten. Correlation between the two feeding parameters is also shown. Herbivory treatments are depicted by different symbols.