Parasite dilution occurs in varied systems, via multiple potential mechanisms. We used laboratory manipulation and field surveys to test for invader-induced parasite dilution via two specific mechanisms: host–host competition and encounter reduction. In the laboratory, single Aedes triseriatus larvae were exposed to one of eight combinations of: parasitic Ascogregarina barretti, +/−1 cohabiting Aedes albopictus larva during parasite exposure, and +/−1 cohabiting A. albopictus larva after infectious parasite removal. Larval infection intensity (predicted to decrease via dilution by encounter reduction) was not significantly affected by A. albopictus. Adult infection prevalence and intensity (predicted to decrease via dilution by host–host competition) were significantly greater with A. albopictus, suggesting parasite amplification by interspecific competition, an effect potentially mediated by competition increasing A. triseriatus development time. In the field, we tested for effects of potential dilution host abundances on prevalence and abundance of A. barretti in A. triseriatus larvae. Piecewise path analysis yielded no evidence of host–host competition impacting parasitism in the field, but instead indicated a significant direct negative effect of Aedes spp. abundance on parasite abundance in A. triseriatus, which is consistent with dilution via encounter reduction in the field, but only in tree holes, not in man-made containers. Our results are consistent with the hypothesis that a noncompetent invader can alter the native host–parasite relationship, but our laboratory and field data yield differing results. This difference is likely due to laboratory experiment testing for per capita effects of dilution hosts on parasitism, but field analysis testing for effects of dilution host abundance on parasitism. Individually, host–host competition with the invader amplifies, rather than dilutes, parasite success. In contrast, our path analysis is consistent with the hypothesis that dilution of parasitism results from increased abundance of noncompetent hosts in the field.

中文翻译：

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不合格的宿主如何导致寄生能力减弱？测试本地和入侵蚊子的假设


寄生虫稀释通过多种潜在机制发生在不同的系统中。我们利用实验室操作和实地调查，通过两种特定机制来测试入侵者引起的寄生虫稀释：宿主间竞争和遭遇减少。在实验室中，将单只三列伊蚊幼虫暴露于以下八种组合中的一种：寄生性Ascogregarina barretti 、在寄生虫暴露期间+/-1 同居的白纹伊蚊幼虫，以及去除传染性寄生虫后+/-1 同居的白纹伊蚊幼虫。幼虫感染强度（预计通过遭遇减少而稀释而降低）并未受到白纹伊蚊的显着影响。白纹伊蚊的成虫感染流行率和强度（预计通过宿主间竞争稀释而降低）明显更高，这表明寄生虫通过种间竞争而放大，这种效应可能是由竞争增加三纹伊蚊发育时间介导的。在现场，我们测试了潜在稀释寄主丰度对三列蝽幼虫中巴雷蒂蝽流行率和丰度的影响。分段路径分析没有得出宿主间竞争影响田间寄生的证据，而是表明伊蚊有显着的直接负面影响。 A. triseriatus中寄生虫丰度的丰度，这与田间遭遇减少造成的稀释一致，但仅限于树洞中，而不是人造容器中。我们的结果与以下假设一致：无能力的入侵者可以改变本地宿主与寄生虫的关系，但我们的实验室和现场数据产生了不同的结果。 这种差异可能是由于实验室实验测试了稀释宿主对寄生的人均影响，但现场分析测试了稀释宿主丰度对寄生的影响。就个体而言，宿主与入侵者之间的竞争会放大而不是削弱寄生虫的成功。相比之下，我们的路径分析与寄生性稀释是由于田间非活性宿主丰度增加所致的假设是一致的。