Fungal Endophyte-Mediated Antibiotic and Antixenotic Plant Resistance to Herbivorous Insects

Endophytic fungi reside within both above- and below-ground plant tissues and play pivotal roles in modulating plant fitness and immunity, particularly in the context of plant-insect interactions. They mediate plant defences through the production of bioactive compounds and the alteration of plant physiology, leading to antibiotic (affecting herbivore growth and survival) and antixenotic (deterring herbivore settlement) effects. This review synthesises current evidence on the mechanisms underlying these endophyte-mediated effects, highlighting how these interactions shape herbivore behaviour and performance. Antibiotic effects emerge through the production of secondary metabolites that disrupt herbivore digestion, development and reproduction. Simultaneously, antixenotic responses are driven by multiple mechanisms, including the synthesis of secondary metabolites, changes in plant surface chemistry and volatile emissions that reduce herbivore preference. In addition to their direct impact on herbivores, endophyte-mediated responses can influence higher trophic levels by enhancing plant attractiveness to natural enemies of herbivores, such as parasitoids and predators. These multifaceted defence strategies not only reduce herbivore damage but also contribute to broader ecological dynamics by mediating communication between above- and below-ground plant compartments. Understanding these effects is critical for advancing Integrated Pest Management (IPM) strategies, as endophytes offer a sustainable and environmentally friendly alternative to chemical pesticides.