Sawfly larvae of the tribe Phymatocerini (Hymenoptera: Tenthredinidae), which are specialized on toxic plants in the orders Liliales and Ranunculales, exude a droplet of deterrent hemolymph upon attack by a predator. We investigated whether secondary plant metabolites from Ranunculaceae leaves are sequestered by phymatocerine Monophadnus species, i.e., Monophadnus alpicola feeding upon Pulsatilla alpina and Monophadnus monticola feeding upon Ranunculus lanuginosus. Moreover, two undescribed Monophadnus species were studied: species A collected from Helleborus foetidus and species B collected from Helleborus viridis. Comparative high-performance liq. chromatog.-photodiode array detection-electrospray ionization-mass spectrometric analyses of plant leaf and insect hemolymph exts. revealed the presence of furostanol saponins in all samples. Larvae of species A and B actively sequestered (25R)-26-[(α-L-rhamnopyranosyl)oxy]-22α-methoxyfurost-5-en-3β-yl O-β-D-glucopyranosyl-(1→3)-O-[6-acetyl-β-D-glucopyranosyl-(1→3)]-O-β-D-glucopyranoside (compd. 1). This compd. occurred at a 65- to 200-fold higher concn. in the hemolymph of the two species (1.6 and 17.5 μmol/g FW, resp.) than in their host plant (0.008 and 0.268 μmol/g FW, resp.). In M. monticola, compd. 1 was found at a concn. (1.2 μmol/g FW) similar to that in the host plant (1.36 μmol/g FW). The compd. could not be detected consistently in M. alpicola larvae where, however, a related saponin may be present. Addnl. furostanol saponins were found in H. foetidus and H. viridis, but not in the two Monophadnus species feeding on them, indicating that sequestration of compd. 1 is a highly specific process. In lab. bioassays, crude hemolymph of three Monophadnus species showed a significant feeding deterrent activity against a potential predator, Myrmica rubra ant workers. Isolated furostanol saponins were also active against the ants, at a concn. range similar to that found in the hemolymph. Thus, these compds. seem to play a major role for chem. defense of Monophadnus larvae, although other plant secondary metabolites (glycosylated ecdysteroids) were also detected in their hemolymph. Physiol. and ecol. implications of the sequestered furostanol saponins are discussed.
Sequestration of furostanol saponins by Monophadnus sawfly larvae
BRACA, ALESSANDRA;
2007-01-01
Abstract
Sawfly larvae of the tribe Phymatocerini (Hymenoptera: Tenthredinidae), which are specialized on toxic plants in the orders Liliales and Ranunculales, exude a droplet of deterrent hemolymph upon attack by a predator. We investigated whether secondary plant metabolites from Ranunculaceae leaves are sequestered by phymatocerine Monophadnus species, i.e., Monophadnus alpicola feeding upon Pulsatilla alpina and Monophadnus monticola feeding upon Ranunculus lanuginosus. Moreover, two undescribed Monophadnus species were studied: species A collected from Helleborus foetidus and species B collected from Helleborus viridis. Comparative high-performance liq. chromatog.-photodiode array detection-electrospray ionization-mass spectrometric analyses of plant leaf and insect hemolymph exts. revealed the presence of furostanol saponins in all samples. Larvae of species A and B actively sequestered (25R)-26-[(α-L-rhamnopyranosyl)oxy]-22α-methoxyfurost-5-en-3β-yl O-β-D-glucopyranosyl-(1→3)-O-[6-acetyl-β-D-glucopyranosyl-(1→3)]-O-β-D-glucopyranoside (compd. 1). This compd. occurred at a 65- to 200-fold higher concn. in the hemolymph of the two species (1.6 and 17.5 μmol/g FW, resp.) than in their host plant (0.008 and 0.268 μmol/g FW, resp.). In M. monticola, compd. 1 was found at a concn. (1.2 μmol/g FW) similar to that in the host plant (1.36 μmol/g FW). The compd. could not be detected consistently in M. alpicola larvae where, however, a related saponin may be present. Addnl. furostanol saponins were found in H. foetidus and H. viridis, but not in the two Monophadnus species feeding on them, indicating that sequestration of compd. 1 is a highly specific process. In lab. bioassays, crude hemolymph of three Monophadnus species showed a significant feeding deterrent activity against a potential predator, Myrmica rubra ant workers. Isolated furostanol saponins were also active against the ants, at a concn. range similar to that found in the hemolymph. Thus, these compds. seem to play a major role for chem. defense of Monophadnus larvae, although other plant secondary metabolites (glycosylated ecdysteroids) were also detected in their hemolymph. Physiol. and ecol. implications of the sequestered furostanol saponins are discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
