DIVERSITY AND MECHANISMS OF INSECTICIDAL ACTION OF ENTOMOPATHOGENIC NEMATODE DERIVED TOXINS: A REVIEW

Abstract

Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis are important biological control agents that exploit mutualistic associations with the bacteria Xenorhabdus and Photorhabdus to rapidly kill insect hosts. These bacterial symbionts produce a diverse array of proteinaceous toxins and non-protein secondary metabolites that contribute to host killing, immune suppression, tissue degradation and cadaver preservation. This review summarizes the diversity of EPN-derived insecticidal compounds and their molecular and cellular mechanisms of action. Major toxin groups, including toxin complexes (Tcs), Makes-Caterpillars Floppy (Mcf) toxins, Pir binary toxins and Photorhabdus virulence cassettes (PVCs), together with lipopeptides, polyketides and other secondary metabolites, are discussed. Their insecticidal effects involve pore formation, disruption of the midgut epithelium and cytoskeleton, apoptosis, haemocyte dysfunction, suppression of eicosanoid-mediated immunity and interference with essential cellular processes. Evidence from laboratory and field studies demonstrates activity against insects belonging to several orders, including Lepidoptera, Coleoptera and Diptera, while differences in toxin profiles and host specificity among bacterial species and strains influence their efficacy. Recent advances in genome sequencing, biosynthetic gene-cluster mining, heterologous expression and synthetic biology have expanded opportunities for discovering and developing novel EPN-derived bioinsecticides. However, challenges related to toxin purification, stabilization, formulation, host specificity, non target effects and field performance remain important barriers to commercialization. Overall, EPN-derived toxins represent a chemically and functionally diverse resource with considerable potential for developing sustainable and innovative insect pest management strategies.