White grub, Polyphylla olivieri Cast. (Col., Melolonthidae) is major pest of the Iran. In a survey for collecting natural entomopathogenic nematodes associated with this melolonthid, two isolates of Steinernema spp. were collected as natural pathogens in larval populations of the white grub in the Tehran province of Iran. Morphological characters identified those as members of “carpocapsae “group. Morphological and molecular characters using ITS sequences as well cross hybridization tests confirmed those as S.carpocapsae.16S rRNA sequences and phenotypic characters of symbiotic bacteria were determined and used for identification. Phylogenetic analysis for studying relationship was performed. This is the first information about this pathogen of P.olivieri as well new information about symbiotic bacteriua associated with Iranian entomopathogenic nematodes.

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