RESILIENCE BENEATH THE SURFACE: MOLECULAR ADAPTATIONS TO ENVIRONMENTAL STRESS IN ENTOMOPATHOGENIC NEMATODES

Abstract

Entomopathogenic nematodes (EPNs), principally belonging to the genera Steinernema and Heterorhabditis, are important biological control agents because of their ability to infect and kill a broad range of economically important insect pests. Their infective juveniles (IJs), which represent the free-living and environmentally exposed stage, must survive fluctuating temperature, soil moisture, ultraviolet radiation, osmotic stress, hypoxia, nutritional limitation and other biotic and abiotic constraints before locating a suitable insect host. Consequently, environmental stress tolerance is a major determinant of EPN persistence, infectivity and field performance. Recent studies have demonstrated that environmental adaptation is associated with coordinated physiological, biochemical, transcriptional, genomic and post transcriptional responses. Heat-shock proteins, trehalose, late embryogenesis abundant proteins, antioxidant enzymes, lipid remodeling, metabolic reprogramming and stress-responsive transcripts contribute to tolerance of adverse conditions. Comparative transcriptomic and genomic studies have further demonstrated considerable interspecific and intraspecific variation in stress tolerance, suggesting that environmental history and genetic background influence adaptive phenotypes. Small RNAs and neuropeptide-associated regulatory networks provide an additional molecular layer potentially underlying behavioural plasticity. Although direct evidence for DNA methylation and histone-mediated regulation in EPNs remains limited, epigenetic regulation in their bacterial symbionts and extensive non-coding RNA repertoires in EPN genomes provide promising directions for future research. This review synthesizes current knowledge of the molecular mechanisms underlying environmental adaptation and stress tolerance in Steinernema and Heterorhabditis, with particular emphasis on thermal stress, desiccation, oxidative stress, ultraviolet radiation, infective juvenile biology, host-finding behaviour, virulence, EPN–symbiont interactions and multi-omics approaches.