ABSTRACT
Entomopathogenic nematodes (EPNs) of the genus Steinernema are obligate insect parasites that inhabit soil ecosystems and form symbiotic associations with bacteria of the genus Xenorhabdus. Accurate identification of the nematodes is essential for their effective application in biological control programs. In the present study, we investigated the morphology of the infective juvenile (IJ) stage of Steinernema adamsi, a recently reported novel EPN species from Thailand, using compound light microscopy and scanning electron microscopy (SEM). The nematodes were previously identified by molecular analyses and were maintained in the laboratory through repeated infection cycles using Galleria mellonella as the insect host. Morphometric analysis showed that the IJs had a mean body length of 946.57 μm. SEM observations revealed that the lateral field of the IJ possesses eight distinct longitudinal ridges at the mid-body region. This study represents the first SEM-based description of the IJ stage of S. adamsi. The combined morphological observations presented here provide additional diagnostic information and contribute to more accurate identification of entomopathogenic nematodes.