CAN PLANTS GAIN PROTECTION FROM HERBIVORY BY ASSOCIATION WITH UNPALATABLE NEIGHBORS - A FIELD EXPERIMENT IN A WILLOW-SAWFLY SYSTEM

The fact that the spatial association of plants can influence the risk of herbivory has received little interest from ecologists. We tested the prediction, generated by patch use theory, that plants can gain pr otection from herbivory when associated with plants of lower palatabil ity. Nine clones (referred to as matrix-clones) of the willow Salix la siolepis were identified in the held. Twenty-seven potted willows (S. lasiolepis) originated from three different clones (9 potted willow fr om each clone) were selected in such a way that intra-clonal variation in age, size and morphology (number of branches and last year shoots) was minimised. Prior to sawfly egg-laying we placed three potted indi viduals, one of each clone origin, inside each matrix-clone. The densi ties of the stem galler Euura lasiolepis, the petiole galler Euura sp. and the leaf folder Phyllocolpa sp. were measured on the matrix-clone s and on the potted willows. For stem gallers, but not for petiole gal lers and leaf folders, we found positive correlation between sawfly de nsity on the matrix-clones and sawfly density on the potted willow. Th us, as predicted the potted willows seemingly gained protection from s tem gallers by association with neighbours (matrix-clones) of low pala tability. However, only one of three tests supported our predictions. On balance we should therefore reject our hypothesis. Still, it might be too early to totally discard this hypothesis. More case studies are needed before a final evaluation can be done. There was a strong corr elation between clone origin, shoot length and sawfly densities for th e pelted willows, suggesting an underlying genetic variation among clo nes in susceptibility to sawfly oviposition.