We study how a native herbivore has responded to an introduced species of host plant. In the early 1900s, "devil's claw", a plant native to the southwestern United States, was introduced to the southeastern United States. Tobacco hornworms (Manduca sexta) have since adopted this atypical introduced host plant (typically hornworms are restriced to feeding on plants belonging to the Solanaceae, or nightshade plant family, to which devil's claw does not belong).
We have found that wild populations of M. sexta will lay eggs on devil's claw, however this comes at a cost of severe reductions in survival, performance and fitness.
Why then has M. sexta adopted devil's claw as a host plant? In some populations, the poor diet quality of devil's claw is offset by escape from an important braconid parasitoid natural enemy, Cotesia congregata: a high rate of parasitism on typical solanaceous host plants offsets the poor intrinsic performance on devil's claw resulting in comparable total fitness of M. sexta reared on both host plants.
Additional aspects of the environment can further modify the adoption of devil's claw as a host plant. For example, the typical negative relationship between body size and temperature (temperature-size rule) is reversed on devil's claw. The reversal of the temperature-size rule on devil's claw, may facilitate the adoption of devil's claw in regions with relatively warm climates. More generally, these results reinforce the fact that how species respond to novel environments is the outcome of multifarious factors that can sometimes interact in surprising ways.