Iridoid glycosides of Chelone glabra (Scrophulariaceae) and their sequestration by larvae of a sawfly, Tenthredo grandis (Tenthredinidae)

Analysis of Chelone glabra (Scrophulariaceae) by gas chromatography showed that leaves of this plant contained primarily the iridoid glycoside catalpol, and in a few individuals some aucubin was also detected. There was no difference in the iridoid glycoside content of damaged compared to undamaged plants, nor was there a difference between plants collected from a population in Leverett, Massachusetts, and those from plants in an experimental garden in Cambridge, Massachusetts. Larvae and prepupae of the sawfly, Tenthredo grandis (Tenthredinidae) contained catalpol sequestered from the larval host plant. The exuvia also contained catalpol, whereas the frass contained only aucubin. These results indicate that larvae of this sawfly selectively sequester catalpol, eliminating the aucubin in the frass.