A central question in the study of plant-insect interactions is why herbivorous insects tend to restrict their feeding to a limited range of hosts. The goal of the proposed research is to address this question of specialization by comparing a generalist herbivore's performance on several possible hosts in terms of both host quality and the rate of attack by natural enemies. Preliminary investigations have demonstrated that Vanessa cardui's growth is poor on its preferred host relative to other available hosts, suggesting that host quality is relatively less important than other ecological factors in determining its host preferences. The potential role of natural enemies in determining host preferences has been forcefully stated but remains relatively depauperate of experimental study. The possibility of a latitudinal gradient in importance of natural enemies is suggested and will be investigated by comparing variation in V. cardui's host preferences and the rate of attack by natural enemies in several sites. A generalist herbivore has been chosen for this study to obtain an unobscured view of the herbivore's performance on a variety of hosts before the herbivore has had significant time to adapt to its host in multiple dimensions.
