SEQUESTRATION OF VERATRUM ALKALOIDS BY SPECIALIST RHADINOCERAEA-NODICORNIS KONOW (HYMENOPTERA, TENTHREDINIDAE) AND ITS ECOETHOLOGICAL IMPLICATIONS

The larvae of the specialist sawfly Rhadinoceraea nodicornis Konow (Hy menoptera, Tenthredinidae) store in their hemolymph ceveratrum alkaloi ds originating from the host plant Veratrum album L. (Liliales, Melant hiaceae). The major alkaloid found in the hemolymph is 3-acetyl-zygade nine. 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 i n 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 lar vae is fourfold: direct sequestration, metabolism followed by sequestr ation, 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 leav es. Bioassays with the ant Myrmica rubra L. proved that the hemolymph of R. nodicornis larvae is highly deterrent and toxic. In bioassays ev aluating defensive efficiency against predators (ants, spiders, and bu shcrickets), no larvae were eaten. Ceveratrum alkaloids were also dete cted in the hibernating prepupae of R. nodicornis. In feeding bioassay s, the shrew Crocidura russula Hermann rarely fed upon prepupae, sugge sting 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. Bioassay s and field observations enable us to suppose that R. nodicornis and i ts enemies produce a food web of ion connectance.