Repeated damage by specialist insects suppresses the growth of a high tolerance invasive tree.
Many invasive plant species have high tolerance to herbivore damage, which can lead to low impacts of introduced biological control insects. High herbivore tolerance may be a trait acquired by invasive plants in their invaded range which makes it difficult to predict impacts of introduced insects. In this study, we compared the growth and foliar secondary chemical responses of invasive and native populations of Triadica sebifera (Chinese tallow tree) to repeated damage by specialist or generalist herbivores. We found repeated damage significantly decreased plant biomass and increased foliar tannin and flavonoid concentrations compared to a single damage event. These effects were significantly stronger with specialist damage than with generalist damage but the magnitudes of these differences were small. Plants from invasive populations had lower foliar tannins and higher foliar flavonoids than plants from native populations and had greater biomass in every damage treatment. Our results suggest that repeated damage could suppress the growth of invasive plants with high tolerance. Thus using multivoltine herbivores as biological control agents may overcome herbivore tolerance and increase biological control efficacy.