Mycorrhizal benefits on plant growth and protection against Spodoptera exigua depend on N availability

Mycorrhizal symbiosis influences plant growth and nutrition and can affect the performance of insect herbivores, but these effects are context-dependent. This study aims to investigate the influence of nitrogen fertilization and mycorrhizal symbiosis on maize and Spodoptera exigua performance and to explore the potential underlying mechanisms. Mycorrhiza promoted maize growth and reduced S. exigua performance, but these effects were dependent on nitrogen availability. We then assessed whether the consequences for S. exigua were mediated by its gut microbiota. Neither nitrogen nor mycorrhization affected S. exigua gut bacterial community. Reduced herbivore performance was instead potentially due to the effects of nitrogen-mycorrhiza interaction on the plant nutritional value.