The susceptibility of potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) to native and commercial strains of entomopathogenic nematodes (EPNs) was studied under laboratory conditions. Native strains of EPNs were collected from north eastern Iran and characterized as Steinernema feltiae and Heterorhabditis bacteriophora (FUM 7) using classic methods as well as analysis of ITS and D2/D3 sequences of 28S genes. Plate assays were performed to evaluate the efficiency of five EPN strains belonging to four species including S. carpocapsae (commercial strain), S. feltiae, S. glaseri and H. bacteriophora (FUM7 and commercial strain). This initial assessment with 0, 75, 150, 250, 375 and 500 IJs/ml concentrations showed that S. carpocapsae and H. bacteriophora caused the highest mortality in both larval and prepupal stages of P. operculella, PTM. Thereafter, these three strains (i.e. S. carpocapsae and H. bacteriophora FUM7 and the commercial strain) were selected for complementary assays to determine the effects of soil type (loamy, loamy-sandy and sandy) on the virulence of EPNs against second (L2) and fourth instar (L4) larvae (as well as prepupae. A soil column assay was conducted using either 500 or 2000 IJs in 2 ml distilled water. Mortality in L2 larvae was not affected by the EPN strain or soil type, while there was a significant interactive effect of nematode strains and soil type on larval mortality. The results also showed that EPN strains have higher efficiency in lighter soils and caused higher mortality on early larvae than that in loamy soil. In L4 larvae, mortality of PTM was significantly influenced by nematode strain and applied concentration of IJs. The larval mortality induced by S. carpocapsae was higher than those caused either by a commercial or the FUM 7 strain of H. bacteriophora. Prepupae were the most susceptible stage.

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