The pistachio root beetle, Capnodis cariosa hauseri causes general weakness in the pistachio trees and may even kill the infected trees. This insect was distributed in many pistachio growing regions of Iran and causes heavy damage to pistachio trees, particularly when the infection is accompanied by gummosis. Cryptic behavior of the larvae reduce efficacy of common control methods. Due to hidden habitat of pest and penetration ability of entomopathogenic nematodes (EPNs) to these habitat types of some insects, we investigated efficacy of two EPN species, Heterorhabditis bacteriophora and Steinernema carpocapsae against last instars larvae of the pest in laboratory. Pathogenicity test in petri dish were performed with five concentrations: 5, 10, 25, 50 and 100 infective juveniles (IJs) per larva. The LC 50 values indicated that S. carpocapsae (12.6 IJs/larva) was comparatively more virulent than H. bacteriophora (17.1 IJs/larva) against C. cariosa larvae after 72 h. Larval mortality was significantly influenced by the EPN species and concentration. The highest mortality were recorded at the concentration of 50 IJs/larva for S. carpocapsae (97.1%). Both EPNs successfully penetrated and reproduced in the C. cariosa larvae at the concentrations of 5 and 25 IJs/larva. The highest reproduction rate was recorded for H. bacteriophora at 5 IJs/larva in C. cariosa (562,881.5 ± 7,773.1 IJs) and the highest penetration into C. cariosa was observed for S. carpocapsae at 25 IJs/larva (19 IJs). The current study demonstrated susceptibility of C. cariosa to both nematode species as well as their reproduction capability and penetration on the pest larva.

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