It is well known that the interactions of insect herbivores and their host plant can be mediated by microbes. Our central hypothesis is that herbivore-associated fungi might directly or indirectly affect plant–insect interactions. In this study, we identified five orally secreted fungi from field-collected black cutworm, Agrotis ipsilon, including Aspergillus parasiticus, Aspergillus niger, Geotrichum candidum, Fusarium subglutinans, and Mucor circinelloides f. lusitanicus. We found that caterpillars inoculated with F. subglutinans or M. circinelloides f. lusitanicus induced higher defense responses in plants, but with different patterns between different plants. These herbivore-induced defense responses reduced the growth of caterpillars. However, direct application of fungi to mechanically wounded tomato did not induce JA-related defense responses. The application of regurgitant from fungi-inoculated or non-inoculated caterpillars, suggested that regurgitant might be responsible for the fungi-mediated defense response in plants against caterpillar attack. Furthermore, both F. subglutinans and M. circinelloides f. lusitanicus benefited caterpillar growth when they fed on detached tomato leaves, but had no influence when caterpillars fed on artificial diet. Our finding suggests that insect-associated fungi could influence plant–insect interactions by indirectly mediating plant defense responses, and directly affecting caterpillar performance on host plants.

中文翻译：

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黑线虫Agrotis ipsilon口腔分泌物的真菌介导植物与昆虫的相互作用

众所周知，昆虫食草动物与其宿主植物之间的相互作用可以通过微生物来介导。我们的中心假设是，草食动物相关真菌可能直接或间接影响植物与昆虫的相互作用。在这项研究中，我们发现，从现场采集的小地老虎，五种分泌的真菌小地老虎，包括寄生曲霉，黑曲霉，白地霉，镰刀subglutinans和毛霉F。lusitanicus。我们发现接种该毛虫F. subglutinans或M.卷枝F。卢西塔尼库斯在植物中诱导较高的防御反应，但不同植物之间的模式不同。这些草食动物诱导的防御反应减少了毛虫的生长。但是，将真菌直接施用到机械损伤的番茄上并不会引起JA相关的防御反应。接种真菌的或未接种的毛毛虫的反刍动物的应用表明，反刍动物可能是真菌介导的植物抵御毛毛虫攻击的防御反应的原因。此外，两个F. subglutinans和M.卷枝F。卢西塔尼库斯当它们以离体的番茄叶为食时，对毛虫的生长有益；而当以人工饮食为食时，对毛虫没有影响。我们的发现表明，昆虫相关真菌可通过间接介导植物防御反应并直接影响宿主植物上的毛毛虫表现来影响植物与昆虫的相互作用。