Tomato is one of the most important crops worldwide. In Egypt, it occupies the largest cultivated area of vegetable crops. There are numerous insect pests attacking tomato crops in Egypt and they cause significant yield loss. The main tomato insect pests in Egypt are the Egyptian cotton leafworm Spodoptera littoralis (Boisduval), the black cutworm Agrotis ipsilon (Hufnagel), the cotton bollworm Helicoverpa armigera (Hübner), the Tomato leaf miner, Tuta absoluta (Meyrick), and the whitefly

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... a tabaci (Gennadius). The mentioned insect species form a widespread complex which commonly attacks tomato crop in open fields and greenhouses, often more or less concurrently. Nowadays, the main control strategies are based on chemical insecticides with all known negative effects. Therefore, this thesis aimed to introduce a biological control system based on Entomopathogenic nematodes (EPNs) to be utilized against the "Egyptian Tomato insect Pest Complex" (ETPC) in order to have an environmentally sound alternative. The work started by screening 15 EPN isolates against the four lepidopteran pests (Chapter II). The objective of the performed screening was to find EPN isolates able to infect all ETPC effectively. The target insect species have many similarities such as their feeding behavior, the destructive stage, and the time of attack. Therefore, standard sand bioassays were performed at four doses against larvae of the target species. Based on the obtained results, the most virulent isolates were Steinernema carpocapsae BA2, S. feltiae Sf, S. abbasi abb, and S. carpocapsae J7. The second step was testing the efficacy of the selected isolates against the whitefly B. tabaci (Chapter III). The isolate S. feltiae Sf was the most efficient one against 2nd nymphal instars of the whitefly. The efficacy of the selected four EPN isolates was tested against T. absoluta in sand and tomato leaf bioassays (Chapter IV). T. absoluta was selected as the key target among ETPC because of its economic importance. Limited differences were [...]