Biological invaders often are accompanied by co-invasive parasites that can alter ecosystem function and established native host-parasite relationships. When these co-invasive parasites establish in a community, they can affect native host fitness and native parasite infection intensity, prevalence, and success within the native host. The mosquito, Aedes triseriatus, is North American host to protozoan parasite, Ascogregarina barretti. In geographic regions invaded by the mosquito Aedes albopictus, A. triseriatus may also be infected by A. albopictus’ co-invasive parasite, Ascogregarina taiwanensis. We tested the hypotheses that: (1) The presence of a co-invasive parasite will negatively affect native parasite fitness, yielding decreased infection intensity, prevalence, and infection success, which could be caused by immune induction of the host or inter-parasite competition, and (2) Coinfection with the native and co-invasive parasites will negatively affect host fitness, yielding increased larval development time and decreased survival and reproductive fitness, caused by increased costs of infection. In our coinfection experiments we find that any exposure to the co-invasive parasite resulted in decreased survivorship and increased development time of the host A. triseriatus, with or without coinfection by the native parasite. Exposure to both co-invasive and native parasites yielded reduced native parasite infection intensity in the host larva and reduced native parasite propagule production in the resulting male adults. Together, these results indicate not only the potential for the co-invasive parasite to alter the native host-parasite relationship, but to impact native host population dynamics.

生物入侵者通常伴随着共同入侵的寄生虫，这些寄生虫可以改变生态系统功能并建立原生宿主 - 寄生虫关系。当这些共同侵入的寄生虫在社区中建立时，它们会影响本地宿主的适应性和本地寄生虫感染强度、流行度和在本地宿主内的成功率。蚊子Aedes triseriatus是北美原生动物寄生虫Ascogregarina barretti的宿主。在被白纹伊蚊入侵的地理区域，A. triseriatus也可能被A. albopictus 的共同入侵寄生虫Ascogregarina taiwanensis感染. 我们测试了以下假设：(1) 共同入侵寄生虫的存在会对原生寄生虫的适应性产生负面影响，导致感染强度、流行率和感染成功率降低，这可能是由宿主的免疫诱导或寄生虫间竞争引起的(2) 与本地和共同入侵的寄生虫共同感染将对宿主适应性产生负面影响，导致幼虫发育时间增加，存活和繁殖适应性降低，这是由于感染成本增加所致。在我们的共感染实验中，我们发现任何与共侵入寄生虫的接触都会导致宿主A. triseriatus的存活率降低和发育时间增加，有或没有被原生寄生虫共同感染。暴露于共侵入和天然寄生虫会降低宿主幼虫的天然寄生虫感染强度，并减少最终雄性成虫的天然寄生虫繁殖体的产生。总之，这些结果表明，共同入侵的寄生虫不仅有可能改变原生宿主 - 寄生虫的关系，而且会影响原生宿主种群的动态。