Colonization of invasive shrubs by native caterpillars

Release from natural enemies may provide invasive plants with a competitive advantage over native taxa. However, such advantages may be short lived: as introduced species increase in abundance, they may accumulate enemies from the native pool through ecological fitting and evolutionary adaptation. How invasive plants become integrated into native food webs is an important question for both basic and applied researchers. Our goal is to understand the process of herbivore colonization and its consequences for the invasive shrubs Amur honeysuckle (Lonicera maackii) and autumn olive (Elaeagnus umbellata). We surveyed and reared caterpillars on invasive and native shrubs/trees in Southwest Ohio. We found that the two invasive plants host diverse caterpillar assemblages with no significant difference in abundance or richness between native and invasive plant species. Caterpillar communities were generally dominated by generalists, however native plants had a higher proportion of specialists. Herbivory was significantly lower on the invasives, although herbivory levels were well within the range typically observed on native woody plants. Our results indicate that diverse communities of caterpillars have colonized these two invasive shrubs and the window of enemy release may be closing.