Insect - fungus interactions: diversity, ecology, and applications

The coevolution of insects and fungi over more than 400 million years has produced a remarkable diversity of ecological associations, spanning obligate mutualisms to antagonistic parasitism. This systematic review synthesizes current knowledge of insect-fungus interactions by integrating ecological, evolutionary, and applied perspectives through a structured literature synthesis and network analysis of documented associations. Multiple independent evolutionary origins of insect-fungus mutualism are identified, with Coleoptera, Hymenoptera, and Blattodea most frequently participating in mutualistic associations. Nutritional mutualisms, such as fungus farming by ambrosia beetles, termites, and leaf-cutter ants, are the most ecologically significant interactions. These are characterized by specialized morphological adaptations (mycangia, fungus combs), enzymatic capabilities for lignocellulose degradation, and co-evolutionary dynamics that have shaped both partners' genomes. Commensal associations, particularly gut-dwelling fungi in aquatic insects, display context-dependent outcomes that may shift toward mutualism under certain environmental conditions. Entomopathogenic fungi, distributed across diverse lineages including Sordariomycetes and Entomophthoromycetes, act as major mortality agents in insect populations and employ sophisticated mechanisms of host manipulation, such as behavioral modification and immune suppression. In addition to their ecological roles, insect-fungus associations have substantial practical applications. Entomopathogenic fungi offer eco-friendly alternatives to synthetic pesticides in biological control. Fungal symbionts contribute to bioremediation through lignocellulolytic and detoxification enzymes. Medicinal fungi, such as Cordyceps species, produce bioactive compounds with pharmaceutical potential. Critical knowledge gaps remain, including the undercharacterized functional diversity of insect-associated fungal communities, the molecular mechanisms underlying host specificity, and the impacts of climate change on interaction outcomes. By integrating network analysis with comprehensive literature synthesis, this review establishes a framework for understanding the ecological and evolutionary significance of insect-fungus associations and highlights their translational potential for sustainable agriculture, biotechnology, and medicine.