Steinernema chainatense n. sp., a new entomopathogenic nematode (Nematoda: Steinernematidae) from Thailand

Abstract

A new entomopathogenic nematode, Steinernema chainatense n. sp., was isolated during sampling in a cassava field in Chai Nat Province, Central Thailand. A combination of morphological, morphometric, and molecular traits places the new species within the longicaudum clade of the glaseri -group. Infective juveniles (IJs) of S. chainatense n. sp. are characterised by a body length of 871 (798–939) μm, a maximum body diameter of 27 (24–30) μm, and a lateral field with eight equally developed ridges at mid-body and a formula of 2, 6, 8, 2. First-generation males are characterised by large, brown spicules, 88 (80–95) μm long, with a well-developed velum. The male genital papillae number 25 in total, comprising 12 pairs and a single midventral papilla. The internal transcribed spacer (ITS) and D2–D3 sequences differ from those of other members of the longicaudum clade by 3.6–10.4% and 1.5–3.5%, respectively. Phylogenetic analysis based on the ITS region of rDNA indicates a close relationship between S. chainatense n. sp. and S. taiwanensis , S. adamsi , S. guangdongense , and S. longicaudum , with S. taiwanensis as its sister taxon. The bacterial symbiont of S. chainatense n. sp. is the recently described Xenorhabdus thailandensis. These morphological and molecular differences support the recognition of S. chainatense n. sp. as a distinct species.