Biological control is a popular tool for invasive species management, but its success in nature is difficult to predict. One risk is that invasive plants, which may have adapted to lower herbivore pressure in the introduced range, could rapidly evolve defences upon re‐association with their biocontrol agent(s). Previous studies have demonstrated that populations of the invasive plant purple loosestrife (Lythrum salicaria) exposed to biocontrol exhibit traits consistent with the rapid evolution of defence. However, to date, no one has tested this hypothesis under field‐natural levels of herbivory. Using seed from 17 populations of purple loosestrife growing in eastern Canada, that varied in their history of exposure to their biocontrol agent, the leaf beetle Neogalerucella spp., we transplanted 1,088 seedlings from 136 maternal families into a common garden under ambient herbivory. Over the following three and half years, we assessed plant performance in the face of biocontrol by measuring early‐season plant size, defoliation, flowering, and season‐end biomass. We discovered that a population history with biocontrol explained little variation in herbivory or plant performance, suggesting that adaptation is not hindering biocontrol effectiveness. Instead, plant size, subsequent defoliation, and spatio‐temporal variables were the main predictors of plant growth and flowering during the study. The high individual variability we observed in plant performance underscores that flexible strategies of allocation and phenology are important contributors to the persistence of invasive plants. Our findings suggest that plant adaptation to biocontrol is unlikely to be a strong impediment to biological control in this species, however, the high survival and variable defoliation of plants in our study also indicate that biocontrol alone is unlikely to result in significant population decline. We recommend that the application of multiple forms of control simultaneously (e.g. thinning plus biocontrol) could help to prevent the existence of refuges of large, reproductive individuals.

中文翻译：

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没有证据表明快速适应会阻碍对入侵植物的生物控制


生物控制是入侵物种管理的常用工具，但其在自然界中的成功很难预测。一个风险是，入侵植物可能已经适应了引入范围内较低的食草动物压力，在与生物防治剂重新结合后可能会迅速进化出防御能力。先前的研究表明，接触生物防治的入侵植物紫色珍珠菜（千屈菜）种群表现出与防御快速进化一致的特征。然而，迄今为止，没有人在野外自然食草水平下检验这一假设。我们使用生长在加拿大东部的 17 个紫珍珠菜种群的种子，这些种群接触生物防治剂Neogalerucella spp. 的历史各不相同，我们将来自 136 个母系家庭的 1,088 颗幼苗移植到环境食草的公共花园中。在接下来的三年半中，我们通过测量早季植物大小、落叶、开花和季末生物量来评估植物在生物防治方面的表现。我们发现，生物防治的种群历史解释了食草或植物性能的微小变化，这表明适应并不妨碍生物防治的有效性。相反，植物大小、随后的落叶和时空变量是研究期间植物生长和开花的主要预测因素。我们在植物表现中观察到的高度个体变异性强调了灵活的分配策略和物候学是入侵植物持久存在的重要因素。 我们的研究结果表明，植物对生物防治的适应不太可能成为该物种生物防治的强大障碍，然而，我们研究中植物的高存活率和可变落叶也表明，单独的生物防治不太可能导致种群数量显着下降。我们建议同时应用多种形式的控制（例如间伐加生物防治）可能有助于防止大型、可繁殖个体的庇护所的存在。