Actu Oecolo@ca 20 (2) (1999) 109- 118 / 0 Elsevier, Paris Palatability of weeds from different European origins to the slugs Deroceras reticulatum Miiller and Arion lusitanicus Mabille Michael Keller, Johannes Kollmann *, Peter J. Edwards Geobotanisches Institut, EI’H Ziirich, Ziirichbergstrasse 38, 8044 Ziirich, Switzerland. * Corresponding author (fax: +41 1 632 1215; email kollrnann@geobot.umnw.ethz.ch) Received August 25, 1998; revisedJanuary 19, 1999; acceptedJanuary 21, 1999 Abstract -As part of a study on the significance of seed provenances in schemes to enhance biodiversity in agricultural habitats, juvenile plants of Cichorium intybus, Daucus carota, Leucanthemum w&are and Silene alba of different European origins were exposed to grazing by two slug species, Deroceras reticulatum and Arion lusitanicus. Living plants were offered in trays, either in a glasshouse (Deroceras) or outdoors (Arion). The amount of herbivory was origin-dependent, with higher losses for all four species from German and Hungarian provenances compared with English and Swiss plants. The main trend was similar for both slug species except in the case of Daucus, and there was a significant ‘origin x plant species’ interaction. We found strong correlations between provenance-specific herbivory and certain climatic characteristics of the corresponding regions, i.e. winter minimum temperatures, and dryness in spring and late summer, which are crucial for the development of slugs. The results can be interpreted in terms of a SW-NE European climatic gradient and may be a consequence of differences in the need for plant defences against herbivory by slugs. Additionally, the data on palatability were compared with susceptibility towards two parasites which occurred in a field exper- iment, a leaf miner on Leucanthemum vulgare and a rust fungus on Silene alba. While specific leaf mining frequencies on Leucanthemum con- trasted with the palatability of the different provenances to slugs, the rust infection on Silene was low on local and German plants, and higher on the more distant provenances from England and Hungary. 0 Elsevier, Paris Choice experiments I climatic traits I ecological compensation sites / ecotypes I plant-herbivore interaction I seed provenance 1. INTRODUCTION In the last decade, the use of wildflower seeds in ecological compensation sites, habitat restoration or re-introduction of species has led to an increasing exchange of seed material between European regions. This practice has been criticized for several reasons [ 1, 241. It is suggested that, besides problems of poor adaptation to the local abiotic environment, interac- tions with associated organisms such as herbivores or pathogens should be a further argument against long- distance seed exchange. As part of a larger project to evaluate the significance of seed provenances for wild- flower strips in agricultural land [29, 301, we investi- gated herbivory by slugs, because these organisms are widespread in agroecosystems throughout Europe and are particularly abundant in wildflower strips [15-l 71. Slugs and snails represent an important selection pres- sure [ 19, 221, which may lead to the evolution of resis- tance to herbivory; they may also be critical for the successful establishment of ecological compensation sites. Slugs are generalized herbivores, since they show no tightly coevolved relationships with their food plants [41]. Yet Dirzo [9] called them ‘acceptability-moder- ated generalists’, as they learn to avoid certain foods after unpleasant or harmful encounters [2, 491, which leads to a distinct hierarchy of preferred food plants. Comparative data on the palatability of various plant species to snails and slugs are available for Derocerus caruanae [9], D. reticulaturn [12, 411, Arion hortensis [13], A. ater [7, 251, A. subfuscus, A. fusciatus [41], Ariolimax columbianus [7] and Cepaea nemoralis U81. One of the principal mechanisms of defence by plants is the accumulation of deterrent chemicals of which phenolics appear especially significant against molluscs [21], but morphological traits, e.g. spines and spicules, may also play a certain role. While hairiness seems to bear no protective property [9, 181, the tissue structure can have an influence, as soft-leaved plants were much more acceptable than those with harder leaves, e.g. for Deroceras caruanae [9]. This could