Notes on the morphology, bionomics, distribution and efficacy of Steinernema siamkayai (Rhabditida: Steinernematidae) from western Uttar Pradesh, India

The entomopathogenic nematode Steinernema siamkayai has been a subject of several detailed studies but its morphological, molecular and ecological characterisation is still incomplete. In the present study we studied morphology of several strains of S. siamkayai using morphometrics and light and scanning electron microscopy (SEM) and we aimed to complete its molecular characterisation by obtaining the sequence of the D2-D3 region of the 28S rDNA in addition to ITS rDNA and mitochondrial (12S and COI) DNA studies. Furthermore, we studied the species life cycle and we attempted to assess its distribution using a meta-analysis of the GenBank records. Finally, insecticidal properties were evaluated against Helicoverpa armigera and Spodoptera litura. The SEM study revealed the presence of the adcloacal pair of genital papillae in males. Duration of the life cycle of the Indian strains did not differ from the previous records; however. we have observed production of the infective juveniles by the first-generation adults. For the first time in entomopathogenic nematodes. we have recorded intra-individual variability in the D2-D3 region of the 28S rDNA and we discuss potential implications of this phenomenon for the use of this marker in EPN systematics. Our analysis of distribution has shown that S. siamkayai is ubiquitous throughout the Indian subcontinent but is rarely found in South East Asia. The pathogenicity results showed that the present species effectively killed the tested pests under laboratory conditions, demonstrating its potential as a biocontrol agent.