Insect herbivory stimulates allelopathic exudation by an invasive plant and the suppression of natives

Exotic invasive plants are often subjected to attack from imported insects as a method of biological control. A fundamental, but rarely explicitly tested, assumption of biological control is that damaged plants are less fit and compete poorly. In contrast, we find that one of the most destructive invasive plants in North America, Centaurea maculosa, exudes far higher amounts of (+/-)-catechin, an allelopathic chemical known to have deleterious effects on native plants, when attacked by larvae of two different root boring biocontrol insects and a parasitic fungus. We also demonstrate that C. maculosa plants experimentally attacked by one of these biocontrols exhibit more intense negative effects on natives.