Occurrence of entomopathogenic nematodes, Oscheius myriophilus Poinar in Thailand: Preliminary characterization of novel isolates and biological control potential against insect pests

Numerous nematodes in the genus Oscheius possess entomopathogenic abilities. These nematodes also kill their insect hosts by releasing their symbiotic bacteria within 48-72 h. In this study, 12 indigenous isolates of Oscheius myriophilus based on molecular, morphological, and morphometric studies were recovered from different undisturbed soils in Thailand. Moreover, the virulence of 12 O. myriophilus at a rate of 25 IJs/cm(2) against fifth-instar larvae of Galleria mellonella ranged from 56%-86% after 72 h of exposure. Oscheius myriophilus EPNKU40 exhibited the highest efficacy in causing mortality in the insect larvae. It also killed third-instar larvae of Spodoptera litura and Spodoptera exigua up to 60% after 72 h of exposure. The median lethal concentration (LC50) values of O. myriophilus EPNKU40 against G. mellonella larvae after 48 and 72 h of exposure were 11 and 4 IJs/cm(2), respectively. The discovery of O. myriophulus is the first record in Thailand characterized using morphological, morphometric, and molecular diagnostic tools, which have shown lethal effects against insect pests and can later be utilized as biocontrol agents after several comprehensive assessments.