Abstract Greater natural enemy diversity generally increases prey mortality. Diversity can be beneficial when natural enemy species occupy distinct niches (complementarity effects) or when diverse communities contain the most impactful species by chance (identity effects). Most research assessing effects of natural enemy diversity focuses on aboveground predators, however, and few studies have assessed whether increased entomopathogen diversity in soil affects belowground herbivores. Here, we assessed effects of entomopathogen richness on herbivore suppression and plant productivity in a system consisting of entomopathogens, wireworm herbivores, and wheat plants. Specifically, in field experiments we varied the richness of four entomopathogen species (two nematodes, two fungi) that attack herbivorous Limonius californicus larvae belowground. We show that the presence of entomopathogens increased wireworm mortality and subsequently increased plant productivity, but a single entomopathogen species, Metarhizium brunneum, had stronger effects than other species (Beauveria bassiana, Heterorhabditis bacteriophora, and Steinernema carpocapsae). Moreover, entomopathogen communities with M. brunneum consistently produced the strongest effects on prey mortality and plant productivity. Our results suggest that diverse entomopathogen communities increased prey infection more than any single species, indicating complementarity occurred. However, increased plant productivity appeared to be driven by species identify effects. Our study shows that the composition of entomopathogen communities had stronger effects on a pest species than species richness, suggesting that careful selection of entomopathogen species for biological control may be more impactful than promoting entomopathogen diversity.

中文翻译：

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土栖病原体群落的组成介导对线虫食草动物和小麦生产力的影响

摘要 天敌的多样性通常会增加猎物的死亡率。当天敌物种占据不同的生态位（互补效应）或当不同的群落偶然包含最具影响力的物种（身份效应）时，多样性可能是有益的。然而，大多数评估天敌多样性影响的研究都集中在地上捕食者身上，很少有研究评估土壤中昆虫病原体多样性增加是否会影响地下食草动物。在这里，我们评估了昆虫病原体丰富度对由昆虫病原体、线虫食草动物和小麦植物组成的系统中食草动物抑制和植物生产力的影响。具体而言，在田间试验中，我们改变了攻击地下食草性 Limonius californicus 幼虫的四种昆虫病原体物种（两种线虫、两种真菌）的丰富度。我们表明昆虫病原体的存在增加了线虫的死亡率并随后增加了植物生产力，但单一的昆虫病原体物种绿僵菌比其他物种（白僵菌、拟杆菌属和 Steinernema carpocapsae）具有更强的影响。此外，具有 M. brunneum 的昆虫病原体群落始终对猎物死亡率和植物生产力产生最强的影响。我们的结果表明，不同的昆虫病原体群落比任何单一物种都增加了猎物感染，这表明存在互补性。然而，植物生产力的提高似乎是由物种识别效应驱动的。我们的研究表明，昆虫病原体群落的组成对害虫物种的影响大于物种丰富度，