Chemical constituents of Erysimum cheiranthoides deterring oviposition by the cabbage butterfly, Pieris rapae

Avoidance of Erysimum cheiranthoides for oviposition by Pieris rapae has been attribute to the presence of water-soluble deterrents. The active material was extracted into n-butanol and isolated by a series of HPLC separations. TLC of the active fraction and visualization of individual constituents with Kedde's reagent indicated that cardenolides are responsible for deterring oviposition. UV spectra were also characteristic of cardenolides. Bioassays of selected known cardenolides revealed a general lack of activity, except for cymarin, which was as strongly deterrent as the most prominent cardenolide isolated in pure form from E. cheiranthoides . The results suggest that cardenolides in this plant can explain its escape from cabbage butterflies, but specific structural features of the glycoside are necessary for oviposition deterring activity.