Identification of Entomopathogenic Nematode isolates from Nigeria and their pathogenicity against the invasive fall armyworm, Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae)
The fall armyworm (FAW, Spodoptera frugiperda J.E. Smith [Lep.: Noctuidae]), a highly destructive lepidopteran pest, poses a serious threat to maize and other staple crops across sub-Saharan Africa. With growing concerns over resistance to synthetic insecticides, entomopathogenic nematodes (EPNs) have emerged as viable biological control alternative. This study reports the isolation, identification, and virulence evaluation of six indigenous EPN isolates collected from different agroecological zones in Nigeria. Morphological and morphometric assessments, supported by molecular analyses of internal transcribed spacer regions (ITS), D2-D3, and mitochondrial gene regions, identified the isolates as Heterorhabditis bacteriophora, Steinernema carpocapsae, S. feltiae, S. nepalense, and Oscheius myriophilus. Virulence bioassays were conducted against four developmental stages of S. frugiperda (2nd, 4th, 6th instar larvae and pupae) using four dosages (25, 50, 100, and 200 infective juveniles [IJs]/insect). All isolates exhibited dose- and time-dependent pathogenicity, with FAWs 2nd instar larvae showing the highest susceptibility. Heterorhabditis bacteriophora (Ib-CRIN68) caused the highest mortality (82.4 {+/-} 5.6%) and the lowest lethal concentration (LC) and lethal time (LT) values among the tested EPN isolates. Significant effects of isolate, dosage, and exposure time on larval mortality (p < 0.001) were found, particularly in early instars. The findings highlight the high biocontrol potential of these Nigerian EPN isolates and underscore the value of integrating molecular and morphological diagnostics for accurate species identification. This work provides a critical foundation for the future ecological characterization and field deployment of indigenous nematodes in sustainable pest management strategies against S. frugiperda in West Africa.