Adam Frew, Pedro Madeira Antunes, Duncan D Cameron, Sue E Hartley, Scott N Johnson, Matthias C. Rillig, Kirk Barnett

The symbiotic association between arbuscular mycorrhizal (AM) fungi and terrestrial plants can enhance plant defences against insect herbivores. Despite advances in our understanding of how AM fungi affect plant tolerance and resistance based defence mechanisms, we contend that the role of fungal diversity in these interactions continues to be largely overlooked. This is problematic considering plants typically associate with multiple AM fungi in both natural and agriculturally managed environments in a way which varies spatially and temporally. While the importance of mycorrhizal fungal diversity is being increasingly incorporated into research efforts across various facets of ecology, progress on how AM fungal diversity mediates plant protection from herbivory is disparate and piecemeal. Here we discuss why it is important to focus efforts on understanding how AM fungal diversity can shape plant defence outcomes and highlight key knowledge gaps to be addressed.