Secondary metabolites as multifunctional molecular weapons: New mechanistic insights into how entomopathogenic fungi suppress insect immunity

Entomopathogenic fungi (EPF) secrete structurally diverse secondary metabolites (SMs) that subvert insect immune defenses to ensure successful infection. Classic examples, such as destruxins, beauvericin, oosporein, bassianolide, tenellin, and cytochalasins, disable both cellular immunity (phagocytosis, encapsulation, nodulation) and humoral defenses (phenoloxidase cascade, antimicrobial peptides, reactive oxygen species) by targeting key immune signaling pathways (Toll, Imd, JAK/STAT). Recent breakthroughs have transformed the field from descriptive toxin lists into mechanistic, systems-level understanding of how individual metabolites act on defined host cells and pathways in vivo. Direct causal evidence indicates, for example, Beauveria bassiana oosporein can both inhibit competing microbes and host immune prophenoloxidase (proPO) activation and antimicrobial peptide (AMP) expression, whereas Metarhizium destruxins can act in host scavenger receptor suppression and hemocyte apoptosis but also inhibition of aminoacyl tRNA synthetases, calcium channels (disrupting ion homeostasis), and cytoskeletal functioning. This review focuses on Hypocrealean EPF SM effects on insect immunity, integrating new advances, and tracing how genetic (e.g., CRISPR-based) manipulation of biosynthetic gene clusters, dual/single-cell host-pathogen -omics, including spatial metabolomics now allow unprecedented resolution of EPF-insect molecular dialogues. We highlight mechanistic diversity across fungal genera and insect orders, the regulatory logic controlling SM production during infection, and the ecological consequences for host range and virulence. By consolidating these developments, this review captures a critical inflection point in EPF biology, which is where chemical ecology, genomics, and immunology now converge. Understanding these newly revealed immunosuppressive mechanisms not only refines our view of fungal pathogenesis but also provides a rational framework for designing next-generation, host-specific biocontrols while assessing potential non-target immune risks.