none During 1996 and 1997, populations of aphids and whiteflies and their parasites were studied in plastic greenhouses under a chemical control program and in those free of pesticides. In the greenhouses free of pesticides, the parasite A. colemani destroyed 14.7% of the aphids. B. tabaci had no effect on the cucumbers during the spring cultivation. However, it attacked the autumn cultivation. The parasite E. mundus killed 30% of these nymphs. The parasite A. colemani parasitized up to 10% of aphids on tomato plants in greenhouses free of chemical pesticides. The parasite E. mundus killed 15.7% of whitefly nymphs. In greenhouses under a chemical pesticides program, aphids and whiteflies were found on the plants at the end of the plantation season, after the pesticide spraying had stopped. Although the pest population was low, the parasite A. colemani parasitized 8% of the aphid population. Whiteflies were not found on tomato plants in greenhouses under extensive pesticides use. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Abiotic factors; Chemical factors; Land and freshwater zones; Palaearctic region Aphidius colemani (Aphidiidae ); Eretmocerus mundus (Aphelinidae ); Hemipteran hosts; Aphidoidea & Bemisia tabaci; Parasite pathogenicity, effect on host mortality; Fertilizers and pesticides; Egypt; Giza Protectorate; Hemipteran host mortality, effect of parasite pathogenicity Bemisia tabaci (Aleyrodoidea ); Aphidoidea; Hymenopteran parasites; Aphidius colemani & Eretmocerus mundus; Parasite pathogenicity & host mortality; Fertilizers and pesticides; Egypt; Giza Protectorate; Hymenopteran parasite pathogenicity & host mortality, effect of pesticides