none no species The larvae of the specialist sawfly Rhadinoceraea nodicornis Konow (Hymenoptera, Tenthredinidae) store in their hemolymph ceveratrum alkaloids originating from the host plant Veratrum album L. (Liliales, Melanthiaceae). The major alkaloid found in the hemolymph is 3-acetyl-zygadenine. Qualitative and quantitative data showed that the plant alkaloid 3-angeloyl-zygadenine is most probably metabolized in the larval gut to zygadenine and then acetylated. A still unidentified alkaloid with a molecular weight of 591 Da was detected in plant leaves as well as in the gut, hemolymph, and excrement of larvae. Protoveratrine A and B, on the other hand, seem to be degraded by the larvae. These findings indicate that the pathway of ceveratrum alkaloids in R. nodicornis larvae is fourfold: direct sequestration, metabolism followed by sequestration, excretion of intact alkaloids, and degradation. In contrast, no ceveratrum alkaloids were detected in the hemolymph and excrement of larvae of the generalist sawfly Aglaostigma sp. fed with V. album leaves. Bioassays with the ant Myrmica rubra L. proved that the hemolymph of R. nodicornis larvae is highly deterrent and toxic. In bioassays evaluating defensive efficiency against predators (ants, spiders, and bushcrickets), no larvae were eaten. Ceveratrum alkaloids were also detected in the hibernating prepupae of R. nodicornis. In feeding bioassays, the shrew Crocidura russula Hermann rarely fed upon prepupae, suggesting that this stage is also protected from predation to some degree. In field surveys, the only parasitoids recorded were two ichneumonid species that are believed to be specialized on R. nodicornis. Bioassays and field observations enable us to suppose that R. nodicornis and its enemies produce a food web of ion connectance. Biochemistry; Nutrition; Diet; Prey; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Land and freshwater zones; Palaearctic region; Europe Cupiennius salei (Araneae ); Tettigonia cantans (Saltatoria ); Crocidura russula (Soricidae ); Insect prey; Rhadinoceraea nodicornis (Hymenoptera); Predator/prey interaction evidence for prey defensive use of plant toxins Aglaostigma (Tenthredinidae); Food plants; Veratrum album; Life history & ecoethology comparisons with food plant specialist Rhadinoceraea nodicornis (Tenthredinidae); Toxins and venoms; Food plant alkaloid sequestration, metabolism & defensive functions; Food plants; Veratrum album; Host specialization & use of plant alkaloids for defence; Comparison with food plant generalist Aglaostigma; Hymenopteran parasites; Hodostates & Mesoleius; Parasite survey, prevalence & evidence for host specificity; Predators; Antipredator function of sequestered plant alkaloids, experimental tests; Switzerland; Berne & Vaud; Food plant specialization & alkaloid use, comparative ecoethology study Hodostates; Mesoleius (Ichneumonidae ); Hymenopteran hosts; Rhadinoceraea nodicornis; Parasite survey, prevalence & evidence for host specificity; Switzerland Formica rufa (Formicidae); Insect prey; Rhadinoceraea nodicornis; Predator/prey interaction evidence for prey defensive use of plant toxins