Sequestration of ingested [C]senecionine-oxide in the exocrine defensive secretions of chrysomelid beetles

(Chrysomelidae) sequesters in its elytral and pronotal defensive secretion the-oxides of pyrrolizidine alkaloids (PA-oxides) from its food plant (Asteraceae). [C]Senecionine-oxide was applied for detailed studies of PA-oxide sequestration. An average of 11.4% of total radioactivity is taken up by individual beetles which had received [C]senecionine-oxide with their food leaves 8 days before. An average of 28.9% of the ingested radioactivity could be recovered from the defensive secretions collected twice, i.e., 5 and 8 days after tracer feeding. The tracer transfer into the secretion seems to be a slow but progressive process as indicated by the high percentage of tracer still recovered from the secretion sampled after 8 days. Chromatographic analysis revealed that [C]senecionine-oxide is the only labeled compound in the defensive secretion. Beetles that fed on tertiary [C]senecionine sequestered only trace amounts of radioactivity (exclusively present as labeled IV-oxide) in their secretions., a species also adapted to PA containing food plants, was shown to sequester [C]senecionine-oxide with the same efficiency as, a specialist feeding on (Apiaceae), rejected PA treated leaf samples already at very low PA concentrations (10 nmol/leaf piece). In both and, [C]senecionine-oxide applied by injection into the hemolymph is rapidly transferred into the glands., not adapted to pyrrolizidine alkaloid containing plants was unable to sequester [C]-senecionine- oxide in the secretion but rapidly eliminated the tracer with the frass. Again, only traces of labeled [C]senecionine-oxide were found in the defensive secretions of the two PA adapted species if labeled senecionine was injected. It is suggested that the beetles are adapted to the-oxide form of PAs, similarly as their food plants, and that they lack the ability to efficiently-oxidize tertiary PAs. No indication for PA synthesis by the beetles was found in tracer feeding experiments with the biogenetic PA precursor putrescine.