Figure 3.

Functional integration of plant secondary metabolites shapes plant–herbivore and tritrophic interactions. Schematic representation of how different functions of secondary metabolites are used by plants, herbivores, and natural enemies of herbivores is shown. Plants use secondary metabolites for multiple purposes, including resistance, regulation, and primary metabolism (see Fig. 2). Recent work suggests that this multifunctionality is mirrored in adapted herbivores, which also use secondary metabolites for multiple purposes, including similar and new functions. Little is known about how adapted natural enemies use secondary metabolites, but multifunctional integration across three trophic levels is likely (Box 2). Circles represent hypothetical individual secondary metabolites (for color code, refer to Figs. 1 and 2). Solid lines indicate metabolic connections within an organism. Dashed lines indicate similar functions of the same compounds in different organisms.