First Report of Oscheius colombianus (Nematoda: Rhabditidae) in the Philippines and Its Virulence Against Different Developmental Stages of the Common Cutworm, Spodoptera litura

Entomopathogenic nematodes (EPNs) of the genera Heterorhabditis and Steinernema are widely used as biological control agents (BCAs) against agricultural insect pests. Recently, nematodes from the genus Oscheius have shown potential as candidates for biological control agents. In this study, two nematode populations from the agricultural fields in Bukidnon, Philippines, were isolated using the traditional insect soil baiting technique with superworm (Zophobas morio). Through morphological, morphometrical, and molecular analyses, these nematodes, labelled as BRT2 and CSS4, were identified as Oscheius colombianus, the country's first record of the species. Preliminary laboratory assays were conducted to evaluate the efficacy of the isolated nematodes against Z. morio larvae. The results showed that the isolate BRT2 exhibited higher efficacy than the isolate CSS4. Isolate BRT2 was tested against different developmental stages of Spodoptera litura and effectively controlled all stages. The fourth and fifth instar larvae showed the highest susceptibility within 72–96 h post-inoculation at various test concentrations (500, 300 and 100 IJs/larvae). However, 2-day-old pupae had the lowest mortality rate among all treatments, with the commercially available Steinernema siamkayai Thai strain (SST1) serving as the standard control. This study highlights the potential of locally isolated nematodes as biocontrol agents for combating different stages of S. litura. The findings contribute to the growing research on EPNs and their applications in agricultural pest management.