Ecological Characterization and Efficacy of Indigenous Entomopathogenic Nematodes Against Spodoptera frugiperda in Nigeria

The successful deployment of entomopathogenic nematodes (EPNs) in biological pest control hinges on their ecological fitness and stress tolerance. In this study, we assessed the ecological traits and efficacy of six indigenous EPN isolates previously identified from distinct agroecological zones in Nigeria, targeting the invasive pest Spodoptera frugiperda (fall armyworm, FAW). The isolates, identified as Heterorhabditis bacteriophora (Ib-CRIN68), Steinernema carpocapsae (Ib-IART45, Ib-ITUC102), Steinernema feltiae (Za-SAM), Steinernema nepalense (Ib-HORT), and Oscheius myriophilus (Ib-FRIN32), were subjected to a series of ecological bioassays to evaluate their performance under temperature variation, moisture stress, oxygen limitation, oxidative stress, and foraging conditions. Results revealed significant inter- and intra-isolate variability in ecological tolerance traits. Optimal infectivity and reproduction were recorded between 25–30°C, while mortality sharply declined at 10°C and 35°C. Foraging ability varied across substrates and soil depths, with S. carpocapsae isolates exhibiting strong host-finding capability under dry and surface conditions. Desiccation and oxidative stress assays also demonstrated the superior resilience of S. carpocapsae isolates, which sustained low mortality under Polyethylenglycol induced water stress and H₂O₂ exposure. Hypoxia assays indicated that all isolates were moderately tolerant to short-term anoxia, but only H. bacteriophora and the S. carpocapsae isolates survived above 50% at 72 h. Our study highlights the relevance of ecological screening as a prerequisite for selecting robust EPN candidate species and isolates suitable for biological control under variable conditions. The findings support the integration of indigenous EPNs into sustainable pest management frameworks in sub-Saharan Africa.