Sequestration ofVeratrum alkaloids by specialistRhadinoceraea nodicornis konow (Hymenoptera,Tenthredinidae) and its ecoethological implications

The larvae of the specialist sawflyRhadinoceraea nodicornis Konow (Hymenoptera, Tenthredinidae) store in their hemolymph ceveratrum alkaloids originating from the host plantVeratrum 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-angeloylzygadenine 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 inR. 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 sawflyAglaostigma sp. fed withV. album leaves. Bioassays with the antMyrmica rubra L. proved that the hemolymph ofR. 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 ofR. nodicornis. In feeding bioassays, the shrewCrocidura 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 onR. nodicornis. Bioassays and field observations enable us to suppose thatR. nodicornis and its enemies produce a food web of ion connectance.