Determinants of seasonal feeding of the generalist snail Arianta arbustorum at six sites dominated by Senecioneae

We investigated the diet constituents of Arianta arbustorum by means of fae cal analysis and regressed their quantity on the availability and quality o f food plants. We studied six sites, all dominated by plants from the Aster aceae tribe Senecioneae. early and later in the growing season, predicting that the snail's food choice would be determined by the presence of the dif ferent secondary compounds found in the Senecioneae. The snails consumed le ss green plant material and more leaf litter in May than in July. Plant wat er and nitrogen content were higher in May. For the May samples. regression s were only significant at sites that excluded Adenostyles alliariae and Ad enostyles alpina; in July, the regression fit was higher at all sites. Of t he measured plant parameters, only quantity (availability) was a consistent ly significant variable in the regressions. Circumstantial evidence suggest ed that plant secondary compounds had a major influence on snail food choic e: fresh-plant consumption increased over the season. as the concentration of many secondary compounds decreased: both plant availability and quality could only explain about half of the observed variation in snail feeding, w hich argues for other hidden factors influencing snail feeding; the dynamic s of feeding of the various senecionean plants were such that A. alliariae and Senecio sp. had a seasonal acceptance whereas Petasites albus was alway s and A. alpina never accepted, and, finally, the detection of a number of snail-deterrent fractions in A. alpina leaves. a plant which was never foun d to be consumed in this study.