OBSERVATIONS on OLEANDER (NERIUM OLEANDER L., APOCYNACEAE) ECOSYSTEM in GIZA, EGYPT

Abstract:
Oleander (Nerium oleander L., Apocynaceae) is an evergreen urbanite shrub, widely used for ornamental purposes in Egypt. Although this plant is naturally protected from several herbivores by its defensive secondary metabolites, it harbors many phytophagous pests. In the present work, a sampling program was conducted for two years, extended from July 1998 to June 2000, in Giza city, Egypt, to study the seasonality of the most common insect pests attacking oleander and to determine some of the major links in the food web based on this plant. Seasonal fluctuations were determined for two pests: the oleander aphid, Aphis nerii (Homoptera: Aphididae), and the striped mealybug, Ferrisia virgata (Homoptera: Pseudococcidae). The highest population level of the former species, A. nerii, was reported between November and March, with two peaks in December and February; the most vulnerable level of aphid population was reported in late spring and during summer months. This contrasted with the population of the mealybug, F. virgata, which exhibited two peaks in July and September in 1998 and July and October in 1999; the lowest population level of the mealybug was reported during winter months. Coexistence of the two species on the same leaf was frequently observed. Some of the major links in the food web of N. oleander in the study area were illustrated through the most common species associated with the shrubs. The web included: leaf-eating oleander hawk moth, Daphnis nerii (Lepidoptera: Sphingidae); flower feeding adult dermestids (Coleoptera: Dermestidae); the sap feeding guild; parasitoids; and predators. Top predators were a crab spider (Thomisidae) and a jumping spider (Salticidae), followed by the spider wasp, Pomilus sp. (Hymenoptera: Pompilidae).