Many researchers have surveyed damages caused by natural enemies in invasive plants in both native and introduced ranges to testing enemy release hypothesis. Although the physiological impact of natural enemies on invasive plants is important, little research has been conducted to compare the impacts between generalists and specialists. In this study, we report our findings on the physiological and morphological impacts of a native specialist insect (Agasicles hygrophila) and two generalist insects (Atractomorpha sinensis and Hymenia recurvalis) in introduced ranges on an invasive plants Alternanthera philoxeroides in both field trials and controlled environments. Resistances of A. philoxeroides against the generalists and the specialist were also studied. We obtained consistent results in both the field trials and the controlled treatments. Both the generalists and the specialist decreased leaf biomass, photosynthesis, leaf nitrogen content and total leaf non-structural carbohydrate content in A. philoxeroides. However, the specialist decreased leaf mass, photosynthesis, and leaf nitrogen content more acutely than the generalists. Moreover, A. philoxeroides increased both leaf lignin and cellulose concentrations upon the generalists’ attack, but only increased cellulose concentration in response to the specialist. Our results revealed that even under the same population density, the specialists from native ranges caused more severe morphological and physiological damages on A. philoxeroides than the generalists in introduced ranges. Which magnified the consequence of invasive plants suffered lower richness and abundance of natural enemy and contributed to superior performance of invasive plants in introduced regions.