Environmental factors that impact the development of infective juveniles of entomopathogenic nematode Steinernema hermaphroditum

Animals sense and integrate complex external cues to make developmental decisions that help them better survive and adapt to their natural habitats. Under environmental adversity, nematodes can enter an alternative developmental pathway to form a diapautic and stress-resistant stage, termed the dauer larvae. While dauer formation has been well characterized in Caenorhabditis elegans, how environmental factors influence the development of analogous stages in parasitic nematode species remains largely unexplored. This study examines how symbiotic bacteria, temperature, and pheromones affect the formation of the infective juvenile (IJ), a dauer-like and infective stage, in the insect-parasitic nematode Steinernema hermaphroditum. In contrast to C. elegans, where dauer entry requires exogeneous pheromone and is promoted by heat, IJ development in S. hermaphroditum does not rely on exogeneous pheromone and is enhanced by reduced temperature. Moreover, the presence and absence of live symbiotic bacterium Xenorhabdus griffiniae functions as an ON-and-OFF switch that regulates IJ formation. Nutrient-rich liver-kidney media that mimics host insect environment showed IJ entry induction in a DAF-22 dependent manner, suggesting that short-chain ascarosides (pheromone) promote S. hermaphroditum IJ formation through a conserved pathways across nematode species. Together, these findings reveal that environmental cues, such as temperature, microbial diet, and pheromone, can be perceived differently or similarly by S. hermaphroditum compared with C. elegans, reflecting species-specific adaptations to distinct ecological niches and life history strategies. Summary StatementParasitic nematodes rely on infective stages for host invasion, yet their developmental triggers remain largely unexplored. This study reveals how environmental cues regulate IJ formation.