The study aimed to evaluate the efficacy of the EPNs against the larvae of Egyptian cotton leaf worm Spodoptera littoralis (Boisduval) and the black cutworm Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) in vitro before in vivo study. The susceptibility of both larval species to the entomopathogenic nematode species, Steinernema monticolum and Heterorhabditis bacteriophora, was evaluated under laboratory conditions. The concentration of 400 IJs/dish for S. monticolum achieved up to 97.77 and 95.55% mortality rates of the 5 larval instars from 2nd to 6th instars of S. littoralis and A. ipsilon, respectively after 72 h. The concentration of 800 IJs/dish recorded larval mortality rates of 41.86 to 100% against 2nd to 6th instars of A. ipsilon larvae, after 72 h. At the lowest concentration (50 IJs/dish), the larvae of S. littoralis were more susceptible to H. bacteriophora than the larvae of A. ipsilon. The data indicated that 200 IJs/dish was the most effective concentration for all larval stages of both insect pests because the mortality percentage was 100%.

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