Toughness is less important than chemical composition of Arbutus leaves in food selection by Poecilimon species

We tested the hypothesis that unavoidably soft young leaves, which are therefore vulnerable to herbivory, should rely heavily on chemical defense to avoid over-consumption by herbivores. Along with area lost to herbivores, parameters related to chemical and mechanical defense were monitored in two evergreen Mediterranean sclerophylls (Arbutus unedo and Arbutus andrachne) during spring and early summer, when newly growing and old leaves co-occur on the same branches. During the lag phase of growth, young leaves were soft, rich in phenolics and gallotannins (up to 50% and 14% w/w, respectively) and highly astringent. During this period, the main consumer, a cricket (Poecilimon sp., Phaneropterinae) fed almost exclusively on the much tougher old leaves, which were low in phenolics (16%), gallotannins (6%) and astringency. During the rapid phase of leaf expansion, toughness increased and phenolics, gallotannins and astringency dropped to levels characteristic of old leaves. At that time, a shift in insect preferences towards young leaves was evident. Nitrogen content was independent of leaf age. We conclude that leaf toughness is less important than chemical composition in the Arbutus-Poecilimon system, where gallotannins may play a decisive role.