The presence or absence of phenolglycosides in Salix (Salicaceae) leaves and the level of dietary specialisation of some of their herbivorous insects

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Abstract
European Salix species fall into at least 2 groups on the nature of the secondary compounds in their leaves. Some species such as S. nigricans, S. purpurea and S. fragilis contain phenolglycosides in their leaves. Additionally, there are species such as S. alba, S. caprea and S. cinerea with leaves containing no phenolglycosides. Using published food plant list for the weevils, the sawflies and the caterpillars of the British moth, I tried to see if the presence or absence of phenolglycosides in the willow leaves is related to the degree of dietary specialisation of the insects feeding on these leaves. The results show that the Salix with phenolglycosides tend to be the food of the specialised herbivores and to be avoided by generalist. Conversely, Salix without phenolglycosides tend to be eaten by more generalist insects and are avoided by the more specialised. Moreover, the faunas of the different Salix species with phenolglycosides in their leaves are more similar to each other than to the faunas of the Salix species having no phenolglycosides in their leaves.