Host - pathogen Interactions in Entomopathogenic Nematode-insect Systems

Abstract

Entomopathogenic nematodes (EPNs), principally species of the genera Steinernema and Heterorhabditis, are important biological control agents that act in association with the symbiotic bacteria Xenorhabdus and Photorhabdus, respectively. This review synthesises host–pathogen interactions across the EPN infection cycle, from host location and recognition to host invasion, bacterial release, immune suppression, nematode reproduction, and the emergence of infective juveniles. Infective juveniles use ambush, cruising, or intermediate foraging strategies and integrate carbon dioxide, host-derived compounds, plant volatiles, and physical cues to locate susceptible insects. After entry into the haemocoel, nematodes and their bacterial symbionts establish infection through coordinated mechanisms involving toxin and enzyme production, tissue degradation, impairment of immune-cell function, interference with melanisation and immune signalling, and modulation by nematode excretory–secretory products. Infection outcomes are further influenced by innate host defences, including phagocytosis, nodulation, encapsulation, melanisation, antimicrobial peptides, and other humoral responses. Environmental conditions, particularly temperature, soil moisture, texture, aeration, pH, and interactions with soil biota, affect infective juvenile survival, movement, infectivity, and persistence. The review also considers constraints related to host susceptibility, formulation, storage, production, cost, and variable field performance, together with research priorities in multi-omics, functional genomics, microbiome interactions, climate resilience, strain improvement, advanced formulations, and precision application. Integrating molecular, ecological, and operational knowledge may improve the reliability of EPN-based biological control within sustainable integrated pest management.