Mechanistic Pathways Linking Arbuscular Mycorrhizal Fungi, Plant Defense, and Insect Herbivores

Arbuscular mycorrhizal (AM) fungi are among the most widespread plant symbionts, shaping plant nutrition, physiology, and interactions with a broad range of insect herbivores. Their effects on plant-insect dynamics, however, are complex and often contradictory. AM fungi may increase plant size and tissue quality, benefiting herbivores; enhance plant tolerance through compensatory growth; promote investment in defensive compounds; or directly interfere with root-feeding insects through metabolite production. Outcomes vary substantially across plant, fungal, and herbivore species, and general patterns such as generalist herbivores performing more poorly on mycorrhizal plants than specialists, and aphids frequently benefiting from AM symbiosis, suggest that AM fungi shift plant defense phenotypes in ways that differentially affect herbivore feeding guilds. Yet the mechanistic basis for these shifts remains poorly resolved.

Recent work has added further complexity to this picture. Herbivores themselves can alter AM fungal colonization through changes in root flavonoid profiles, with light herbivory promoting early colonization and heavy herbivory suppressing it. Studies using mutant plant lines unable to acquire phosphate through the mycorrhizal pathway have shown that AM nutrient acquisition strategy plays a direct role in regulating plant defense and herbivore performance. A growing body of evidence thus points to a bidirectional relationship in which AM fungi shape plant-herbivore interactions, and herbivores, in turn, shape AM fungal responses through plant signaling pathways.

This Research Topic aims to advance a mechanistic, trait-based understanding of AM-mediated plant-insect interactions. We particularly welcome contributions that move beyond biomass-based metrics and single-strain inoculations to explore the signaling, metabolic, and functional trait mechanisms that underlie the diversity of outcomes observed across plant-AM fungus-insect systems.

We invite original research articles, reviews, and perspective pieces on topics including, but not limited to:

• Hormonal crosstalk (jasmonate, salicylate, and auxin signaling) mediating plant responses to simultaneous AM symbiosis and herbivory;

• AM fungal functional traits (nutrient acquisition strategy, carbon demand, secondary metabolite production) as predictors of plant defense phenotypes;

• Plant metabolomics and defense compound profiling in mycorrhizal versus non-mycorrhizal plants under herbivore pressure;

• Bidirectional signaling between foliar herbivory and AM fungal colonization via root flavonoid and other metabolic pathways;

• AM-mediated effects on phloem-feeding insects and other understudied herbivore guilds;

• Trophic cascades: AM fungal effects on natural enemies and higher-level predator-prey dynamics;

• Community-level AM fungal diversity and its consequences for plant defense and herbivore communities;

• Methodological advances in studying tripartite plant-AM fungus-insect interactions.

Article types and fees

This Research Topic accepts the following article types, unless otherwise specified in the Research Topic description:

• Brief Research Report
• Editorial
• FAIR² Data
• Hypothesis and Theory
• Methods
• Mini Review
• Opinion
• Original Research
• Perspective
• ... View all formats

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Article types

This Research Topic accepts the following article types, unless otherwise specified in the Research Topic description:

• Brief Research Report
• Editorial
• FAIR² Data
• Hypothesis and Theory
• Methods
• Mini Review
• Opinion
• Original Research
• Perspective
• Policy and Practice Reviews
• Review
• Systematic Review
• Technology and Code

Keywords: Arbuscular Mycorrhizal Fungi Plant Defense, Mycorrhizal Plant-Insect Interactions, Am Fungi Herbivore Resistance, Mycorrhizal Symbiosis Defense Mechanisms, Plant Fungal Herbivore Signaling

Important note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.