During 2013, a survey was carried out to determine the pathogens of Polyphylla adspersa (Col; Scarabaeidae) in the Mashhad region, North East of Iran. All larval instars of P. adspersa with sign of nematode infection were collected and death larvae were transferred to the White trap. By using this method fifteen nematode isolates were isolated. Among the pathogenic agents, entomophatogenic and parasite nematodes had a moderate frequency. The initial identification of the collected nematodes carried out using morphometric data. Subsequently, molecular identification and phylogenetic analysis were performed using DNA sequences of ITS and 18SrDNA genes. The molecular data indicated that wg10 and wg19 isolates belong to Oscheius genus with 99% bootstraps support. Also, Nblast analysis introduced two isolates wg10 and wg19 as O. rugaolensis. The sequence of 18S gene O. rugaolensis differed with wg10 and wg19 in 8 and 1 nucleotides, respectively. While on the basis of ITS sequences, 7 nucleotides were differed. The phylogenetic relationship was analysed based on bayesian procedure. In the reconstructed phylogenetic tree, wg10 and wg19 isolates were placed together with O. rugaolensis in a clade by 100% bootstraps support. The phylogenetic results from both genes, ITS and 18S, were similar. This is the first report of Oscheius genus for Iran. Despite the free living behavior of this species, it had high virulence on some insect species and higher ability to reproduce on the cadavers of Galleria melonella rather than healthy larvae. Future studies may provide more data about ability of this species as biocontrol agent.

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