<p>The global challenge of excessive pesticide use in pest control has underscored the need for novel entomopathogenic nematodes beyond the well-studied <i>Steinernema</i> and <i>Heterorhabditis</i> genera. In this context, we described two <i>Oscheius</i> species isolated from the Asian bombardier beetle (<i>Pheropsophus jessoensis</i>). The study provides a detailed description and illustration of two new species of the genus <i>Oscheius</i> named <i>O. parapheropsophi</i> and <i>O. teraiensis</i> utilizing light and scanning electron microscopy. Infection observations suggested that <i>Galleria</i> remained initially active, later became sedentary, and eventually moulted into the pupal stage. The nematodes caused deleterious impact on the pupa, but the live <i>Galleria</i> was not affected lethally. However, the nematode populations grew exponentially within the host cadavers, indicating a preference for feeding on dead hosts. This rapid growth suggests a necromenic lifestyle, in which the nematodes thrive on dead hosts rather than actively killing live ones.</p>