The biotic resistance hypothesis asserts that native species may hinder the invasion of exotic species, which can occur either directly or indirectly by influencing interactions between exotic and local species. Aphid-tending ants may play a key role in the indirect biotic resistance to plant invasion. Ants may protect aphids, thus increasing their negative effect on exotic plants, but may also deter chewing herbivores, thus benefiting exotic plants. We studied native aphid-tending ants (Dorymyrmex tener, Camponotus distinguendus, and Dorymyrmex richteri) on exotic nodding thistles (Carduus thoermeri), which are attacked by thistle aphids (Brachycaudus cardui) and thistle-head weevils (Rhinocyllus conicus). We evaluated the impact of ants, aphids, and weevils on thistle seed set. We compared ant species aggressiveness towards aphid predators and weevils and performed ant-exclusion experiments to determine the effects of ants on aphid predators and weevils. We analysed whether ant species affected thistle seed set through their effects on aphids and/or weevils. The ant D. tener showed the most aggressive behaviour towards aphid predators and weevils. Further, D. tener successfully removed aphid predators from thistles but did not affect weevils. Excluding D. tener from thistles increased seed set. Analyses supported a negative indirect pathway between the aggressive D. tener and thistle seed set through aphid populations, while the other ant species showed no indirect effects on thistle reproduction. Therefore, aggressive aphid-tending ants may enhance biotic resistance by increasing aphid infestation on exotic invasive plants. This study highlights the importance of indirect biotic resistance in modulating the success of invasive species.

生物抗性假设认为，本地物种可能会阻碍外来物种的入侵，而外来物种的入侵可以通过影响外来物种与当地物种之间的相互作用而直接或间接发生。蚜虫可能对植物入侵产生间接的生物抗性。蚂蚁可以保护蚜虫，从而增加其对外来植物的负面影响，但也可以阻止咀嚼草食动物，从而使外来植物受益。我们研究了外来点头蓟（Carduus thoermeri）上易生蚜虫的蚂蚁（Dorymyrmex tener，Camponotus distinguendus和Dorymyrmex richteri），它们被蓟蚜虫（Brachycaudus cardui）和蓟头象鼻虫（攻击）圆锥形犀（Rhinocyllus conicus）。我们评估了蚂蚁，蚜虫和象鼻虫对蓟种子集的影响。我们比较了蚂蚁对蚜虫和天敌的侵略性，并进行了蚂蚁排除实验以确定蚂蚁对蚜虫和天敌的影响。我们分析了蚂蚁物种是否通过影响蚜虫和/或象鼻虫而影响了蓟种子。蚂蚁D. tener对蚜虫和象鼻虫表现出最具侵略性的行为。此外，D。tener成功地从蓟中去除了蚜虫的食肉动物，但没有影响到象鼻虫。从蓟中排除D.tener会增加结实。分析支持侵略性丁香球虫之间的消极间接途径蓟种子通过蚜虫种群繁殖，而其他蚂蚁物种对蓟的繁殖没有间接影响。因此，侵害蚜虫的蚂蚁可以通过增加外来入侵植物上的蚜虫侵染来增强生物抵抗力。这项研究强调了间接生物抗性在调节入侵物种成功方面的重要性。