Selective slug grazing on montane meadow plants

1 In order to test the hypothesis that the sensitivity of field populations of the rare perennial Arnica montana to slug attack is due to its high. palatability, we compared Arnica leaves and seedlings with 20 other plant species in greenhouse food choice experiments. 2 When slugs were given a choice of mature plant leaf discs, Arnica montana was one of the food plants most preferred by all three slug species tested. Arion lusitanicus, Arion subfuscus and Deroceras agreste differed only slightly in their preference for particular plant species. Greater differences in acceptability were observed when parameters other than area consumed were evaluated. Arnica seedlings displayed similarly high susceptibility to slug grazing. 3 Morphological factors influence mollusc feeding behaviour, with epidermal cell wall thickness and hairiness related to acceptability. Removing the hairs by shaving the leaves increased the acceptability of one species, Centaurea jacea, 4 Leaves of undamaged Arnica montana plants were preferred to leaves of plants that had been predamaged by partial leaf removal, suggesting that there is an inducible component of chemical defence. 5 We discuss our results in comparison with other food choice experiments and attempt to extrapolate them to mollusc/plant interactions under held conditions.