An important issue about implication of entomopathogens is their interact with the target pest. Therefore survey on physiology and immune response of insect is inevitable. Innate immune in insect divided into cellular and humeral response that humeral response including production of anti -microbial peptide, reactive nitrogen and oxygen and activation of phenoloxydase cascade. In this survey, phenoloxydase activity of wireworm (Agriotes sp) and Galleria mellonalla larvae (as a model species) against native strains of entomopathogenic nematode, H. bacteriophora and S. feltiae have studied. Enzyme activity was measured in time interval post injection. The phenoloxydase level in both species differed in their sensitivity to both EPN species. For both host species, Agriotes sp and G. mellonella , the phenol oxidase level decreased significantly in comparison with the control (dt=l , P~0.05 ) at 16 h and 12 h post injection, respectively. While melanized nematode was found in dissected larvae of Agriotis sp. (23.41% of H. bacteriophora and 5.35% of S. feltiae ) but immune defense of the host could suppress infectivity of EPN so the injected insect died by 24 hour post injection. This process occurred more quickly in G. mellonella and they died by 16 hour post injection. These result indicated that S. feltiae suppress the phenoloxydase cascade during early step of infection but for H. bacteriophora, however faced with 6.4 (OD/mg) of phenoloxidase activity. There was no significant change in its infectivity to Agriotes sp. this study, lead to select suitable and effective species of pathogen against target pest.

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