Characterisation of Steinernema surkhetense and Its Symbiont Xenrorhabdus stockiae and A Note on Its Geographical Distribution

Abstract

Two cultured populations of Steinernema surkhetense are described from India. Morphologically and morphometrically this material agrees with other species of the Carpocapsae-group (presence of short juveniles), especially with S. surkhetense. The morphology was somewhat similar to the original description with the distinguishing feature being the presence of anal swelling in second-generation female specimens but absent in the original specimens. The morphometric measurements were in close proximity to those in the original specimens and the PCA analysis of important morphometric characters demonstrated some variability within the test populations. Molecular studies based on 28S and ITS rDNA confirmed the Indian material is well conspecific Nepali populations of S. surkhetense, however, with Nepali populations, two base pair differences were observed at 376 and 713 positions only in ITS rDNA gene. We performed a molecular and biochemical characterization of the bacterial symbiont of S. surkhetense and the symbiont is closely related to Xenorhabdus stockiae, which is widespread among South Asian nematodes from the ‘‘carpocapsae’’ group. Finally, we mapped its geographical distribution using a meta-analysis of the ITS GenBank records. The distribution of S. surkhetense based on a meta-analysis of the GenBank records showed its presence in the three Asian countries—India, China, and Nepal, with maximum records from the Indian subcontinent. This species is indigenous to the Indian subcontinent, thus could be tested and later used in the biocontrol of insect pests in India