The enemy release hypothesis postulates that non-native species establish and become abundant because coevolved enemies from the native range are missing or greatly reduced in the introduced range. We assessed whether the invasive New Zealand mud snail, Potamopyrgus antipodarum, is released from castrating trematode parasites by comparing prevalence and diversity of trematode parasites in P. antipodarum and co-occurring native snails in the western United States. Consistent with the enemy release hypothesis (1) P. antipodarum was not infected by trematodes at 80% of the sites and, relative to native snails, had low prevalence (4–5%) at the remaining sites, (2) across all sites, mean prevalence of trematodes was nine times lower in P. antipodarum than in co-occurring native snails and, (3) P. antipodarum were infected by half or fewer of the trematode taxa that infected co-occurring native snails. Taken together, our results suggest that fewer trematode infections and fewer trematode taxa in P. antipodarum could contribute to the success of this invasive snail. However, despite the large geographic scale of our survey (32 rivers sampled) and the large number of sites that we visited (n = 82), few sites had either enough snails or trematode parasites in native snails to be informative. Thus, our conclusions are based on a small number of sites (n = 10).

敌人释放假说假设非本地物种得以建立并变得丰富，因为来自本地范围的共同进化的敌人在引入范围内丢失或大大减少。我们通过比较在美国西部P. antipodarum和共生的天然蜗牛中吸虫性寄生虫的患病率和多样性，评估了侵袭性新西兰泥螺Potamopyrgus antipodarum是否从cast割的吸虫性蠕虫中释放。与敌人释放假说相符（1）在80％的位点上，P。antipodarum未被线虫感染，相对于天然蜗牛，其余位点的患病率较低（4-5％），（2）在所有位点上，吸虫的平均患病率为九次降低P. antipodarum（3）Antipodarum（P. antipodarum）被一半或更少感染共生天然蜗牛的吸虫吸虫感染。综上所述，我们的研究结果表明，抗疟原虫中较少的吸虫感染和较少的类群可能有助于这种侵入性蜗牛的成功。但是，尽管我们的调查具有较大的地理规模（采样了32条河流）并且访问的站点数量众多（n = 82），但很少有站点具有足够的蜗牛或原生蜗牛中的吸虫寄生虫来提供信息。因此，我们的结论基于少量站点（n = 10）。