Identification, Virulence and Ecological Characterisation of Indigenous Entomopathogenic Nematodes as Biological Control Agents Against Fall Armyworm (Spodoptera frugiperda) in Nigeria

Smallholder agriculture in Nigeria faces persistent insect pest pressure and a widespread dependence on chemical insecticides in several crop sectors, alongside limited awareness of sustainable alternatives. This researched evaluated the potential of indigenous entomopathogenic nematodes as biological control agents within an integrated pest management approach (IPM), using the Fall armyworm (FAW) Spodoptera frugiperda as a target organism for benchmarking. The work combines three strands of enquiry that are required for practical deployment. These are the socioeconomic conditions for adoption, the biological identification and virulence of local isolates, and the ecological characterisation that determines field fitness. A structured survey of 740 farmers across ten Nigerian states examined awareness, perceptions, and willingness to adopt. Awareness of entomopathogenic nematodes was 12.8%, while 70.9% expressed interest in training. Perceived effectiveness and safety were neutral to moderate, and education showed a modest positive association with willingness to adopt. Cost, availability, and application complexity were the most frequent barriers. Field facing training through videos and on-farm demonstration was preferred. From 202 soil samples collected in Ibadan and Zaria, six nematode isolates were recovered and identified by morphology and molecular markers as Heterorhabditis bacteriophora (Ib-CRIN68), Steinernema carpocapsae (Ib-IART45, Ib-ITUC102), Steinernema feltiae (Za-SAM), Steinernema nepalense (Ib-HORT), and Oscheius myriophilus (Ib-FRIN32). Recovery rates were 3.9 % in Ibadan and 1.4 % in Zaria. Virulence against S. frugiperda was stage and dose dependent. Steinernema carpocapsae isolates produced more than 90% mortality in second instars at 200 infective juveniles per insect within 72 hours. Lethal concentration values for early instars were 40 to 75 infective juveniles, and greater than 150 for pupae. Time to 50% mortality in second instars was 24 to 36 hours for S. carpocapsae. Ecological assays showed peak infectivity and reproduction at 25 to 30°C, with progeny yields above 100,000 infective juveniles per cadaver at 25°C. Steinernema carpocapsae displayed an ambusher strategy, while H. bacteriophora penetrated deeper soil layers with a cruiser profile. Desiccation survival extended to water activity 0.83 to 0.89 for the best isolates, with MW50 between 0.88 and 0.95. Under anoxia, 72-hour survival exceeded 60% for S. carpocapsae and H. bacteriophora. Oxidative stress tolerance was highest in S. carpocapsae. These results indicate robust ecological fitness for the two leading species. The research demonstrates that indigenous S. carpocapsae and H. bacteriophora are strong candidates for biological control of S. frugiperda in Nigerian systems. The combination of farmer willingness to learn, confirmed pathogenicity, and favourable ecological traits outlines a practical pathway for integration into pest management. Future work should prioritise semi field and field validation, development of stable and affordable formulations, and delivery models that align with farmer preferences and local production capacity.