Rose sawfly, Arge ochropus is an important pest of the ornamental plants such as rose and wild rose bushes in northern Iran. Severe infestations can severely stunt or even kill young plants. In this research, we addressed the cellular reactions of A. ochropus larvae against entomopathogenic nematodes, Steinernema carpocapsae (Weiser) and Heterorhabditis bacteriophora Poinar. Initial cell attachments were observed 0.5 hour post injection (hpi) of H. bacteriophora infective juveniles in the rose sawfly larvae, but encapsulation occurred at 22 hpi while melanization was observed after 24 h. In the case of S. carpocapsae, initial attachment of the hemocytes was detected at 18 hpi and encapsulation was detected 24 hpi while no melanization was observed in this nematode. Also, by injection of infective juveniles of H. bactriophora to A. ochropus larvae, the total hemocyte count showed alternating fluctuations at all-time intervals that represents a decrease of hemocytes. Overall, the results showed strong immune responses of the rose sawfly larvae against H. bacteriophora, while these reactions were weaken for S. carpocapsae. Therefore, it could be concluding that S. carpocapsae has more ability to overcome the host defense system. Results of these type of research help us to select the best biocontrol agent.

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