The consequences of leaf damage for subsequent insect grazing on birch (Betula spp.) : A field experiment.

Low levels of artificial damage were imposed on the leaves of Betla pubescens and B. pendula in early summer 1985. Sixteen tress were used and the damage was distributed throughout the canopy in two ways. It was either randomly dispersed on the tree, or restricted to a localised region of the canopy. Up to 250 leaves/tree were damaged and the position of control leaves was marked as appropriate. At the end of the summer the experimental and control leaves were collected for analysis. Subsequent patterns of grazing by naturally-occurring herbivores were affected by the previous damage to the foliage. Fewer artificially-damaged leaves received subsequent insect grazing damage. The frequecy distribution of insect damage to previously-damaged leaves was significantly different from that of the control leaves, and less leaf tissue was removed from those experimental leaves which did receive subsequent insect attack. The evidence presented suggests that wound-induced changes in leaf palatability do occur in B. pubescens and B. pendula in the field and that a major role is to disperse the damage throughout the canopy.