THE RAISON-DETRE OF PYRROLIZIDINE ALKALOIDS IN CYNOGLOSSUM-OFFICINALE- DETERRENT EFFECTS AGAINST GENERALIST HERBIVORES

In this study we tested whether pyrrolizidine alkaloids (PAs) of Cynog lossum officinale serve as antifeedants against herbivores. Total PA N -oxide extracts of the leaves significantly deterred feeding by genera list herbivores. Specialist herbivores did not discriminate between fo od with high and low PA levels. Three PAs from C. officinale, heliosup ine, echinatine, and 3'-acetylechinatine, equally deterred feeding by the polyphagous larvae of Spodoptera exigua. Although the plants mainl y contain PAs in their N-oxide form, reduced PAs deterred feeding by S . exigua more efficiently than PA N-oxides. On rosette plants, the mon ophagous weevil Mogulones cruciger significantly consumed more of the youngest leaves, which had the highest PA level and the highest nitrog en percentage. Larvae of Ethmia bipunctella, which are oligophagous wi thin the Boraginaceae, did not discriminate between leaves. All genera list herbivores tested significantly avoided the youngest leaves with the highest PA levels. In the field, the oldest leaves also were relat ively more damaged by herbivores than the youngest leaves. It is hypot hesized that the skewed distribution of PAs over the leaves of rosette plants reflects optimal defense distribution within the plant.