Evolutionary consequence of indirect interactions among insect herbivores through herbivore-induced plant regrowth

The questions of how the indirect interactions mediated by herbivore-induced plant responses influence trait evolution of herbivores have been poorly investigated. We previously demonstrated that allopatric populations of the willow leaf beetle, Plagiodera versicolora (Coleoptera: Chrysomelidae) could evolutionarily develop divergent preference, according to locally distinct intensity of induced plant regrowth. Our herbivore removal experiment suggested that the local intensity of herbivore-induced regrowth strongly influenced the geographic variation in the plant regrowth response. Furthermore, attack by another herbivore species could induce willow regrowth, which in turn increased the relative fitness of the beetles with strong preference for new leaves compared with the beetles with weak preference. Therefore, we conclude that the plant-utilizing trait of the leaf beetle can evolve in response to indirect effects of other herbivore species mediated by herbivore-induced plant regrowth.