ESTIMATING COSTS AND BENEFITS OF THE PYRROLIZIDINE ALKALOIDS OF SENECIO-JACOBAEA UNDER NATURAL CONDITIONS

We estimated costs and benefits of pyrrolizidine alkaloids (Pa's) in a field experiment with eight clones of genotypes of Senecio jacobaea. Costs associated with Pa's could not be detected: no trade-offs betwee n growth, percentage flowering and number of flowerheads and Pa's were found. Herbivory of the specialist flea beetle Longitarsus jacobaeae was lower in genotypes with high Pa concentrations. Both herbivory by adults and larvae were negatively correlated with Pa concentration. Di fferential attack of genotypes of S. jacobaea with high and low Pa con centrations by L. jacobaeae did not result in fitness differences betw een genotypes.