INTER-SPECIES AND INTRA-SPECIES-DIFFERENCES IN PLANTS AS HOSTS TO TYRIA-JACOBAEAE

The effect of three food plants, Senecio jacobaea L., Senecio vulgaris L. and Tussilago farfara L., and rust infection of two of them on the performance and host choice of Tyria jacobaeae L. was assessed. The n itrogen content of healthy and infected food plants was measured. Larv ae reared on S. vulgaris had a lower relative consumption index and hi gher efficiency of conversion of ingested food than those reared on th e other two species. These differences were correlated with the higher nitrogen content of S. vulgaris compared to T. farfara and S. jacobae a. Larvae reared on T. farfara were significantly smaller at pupation than those reared on the other species. In both larval and adult choic e tests between healthy plants of the three species, S. jacobaea was a lways the preferred host plant. Adults completely avoided T. farfara i n oviposition choice tests. Infection of S. vulgaris with Coleosporium tussilaginis (Pers) Lev. had, no effect on larval performance. Infect ion of S. vulgaris with Puccinia lagenophorae Cooke. caused difference s in larval performance. Infection of T. farfara with C. tussilaginis had a detrimental effect on larval performance: larvae were smaller, f ed for longer and had lower growth rates than those reared on healthy T. farfara. Healthy T. farfara had a higher leaf nitrogen content than the infected T. farfara. In choice tests against healthy leaves, larv ae avoided leaves of both S. vulgar-is and T. farfara infected with C. tussilaginis. Larvae and adults showed no preference between S. vulga ris leaves infected with P. lagenophorae or healthy leaves. In the fie ld, factors such as plant size may be important in dictating adult and larval preference for a particular host plant species. Rust infection of some species influenced larval performance and host choice, demons trating the importance of studying multitrophic aspects of plant - ins ect interactions.