The leopard moth, Zeuzera pyrina L. (Lepidoptera: Cossidae) is the most destructive pest of walnut trees in Iran. Due to the special habitats of cossid millers, the application of entomopathogenic nematodes (EPNs) in the context of integrated pest management approach may offer an efficient safe strategy to suppress outbreaks of this pest. In the present study, the efficacy of Steinernema carpocapsae and Heterorhabditis bacteriophora, commercial products along with an indigenous isolate of EPN from Kerman region, Acrobeloides maximus, was investigated against the insect pest in laboratory, semi-field, and field conditions. Laboratory experiments included the pathogenicity assay in plate and branch using a range of concentrations [5, 10, 20, 50 and 100 infective juveniles (IJs) per larva], as well as host finding behavior of selected EPNs. The LC50 values indicated that S. carpocapsae (6.4 IJs larva−1) was comparatively more virulent compared with that of H. bacteriophora (8.4 IJs larva−1) and A. maximus (12.1 IJs larva-1) against Z. pyrina larvae after 72 h. All three nematodes caused high insect mortality in branch experiments. In a survey of foraging behavior, the proportional response of H. bacteriophora to the quarter with host-associated cues (feces and live larvae of Z. pyrina) was significantly higher compared with that in S. carpocapsae and A. maximusin Petri dishes containing agar 1, 12 and 24 h after EPN application. The applied concentration of EPNs in pathogenicity assessment of these biocontrol agents against Z. pyrina larvae in pots containing walnut seedlings as well as in infested walnut orchards was 300 IJs cm−2 in 25 ml of distilled water which were directly injected into the gallery entrances. The results indicated that all three nematode species were capable of reducing populations of Z. pyrina larvae in both semi-field and field experiments. Dissection of cadavers under the stereomicroscope confirmed nematode infection. Although no significant differences were observed among the nematode species on infection of Z. pyrina larvae in the semi-field and field tests, the virulence of S. carpocapsae and A. maximus was comparatively greater compared with that of H. bacteriophora. In conclusion, our findings demonstrate that all three EPNs are virulent to Z. pyrina larvae; however, S. carpocapsae commercial product shows better efficacy compared with H. bacteriophora and A. maximus. Furthermore, our study provides the first insight into the foraging strategies of EPNs against leopard moth. Consequently, these EPNs could be considered as suitable candidates to be incorporated into IPM programs of the pest.

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