A survey of scale insects and mealybugs on mango trees (Mangifera indica L.) (Anacardiaceae) were carried out in a private mango orchards located in El-Saff, Giza Governorate, during two successive years 2011-2012 for studying the role of mango leaf essential oil and their pure major constituents in interpretating the susceptibility phenomenon of five mango cultivar leaves to infestation with the white mealybug, Icerya seychellarum (Westwod) (Hemiptera: Monophlebidae). The results indicated that, the mango trees were infested by 12 species of scale insects and mealybugs belonging to four families: Diaspididae, Coccidae, Monophlebidae and Pseudococcidae. From the monthly collection, the white mealybug, I. seychellarum was the most dangerous and abundant of the collected species. The selected five mango cultivars are not equally susceptible to I. seychellarum infestation. Fagrikalan mango trees cultivar (cv.) were heavily infested and severely damaged, while trees of Dabsha cv. are approximately complete free from I. seychellarum infestation. However, the susceptibility levels of mango cultivars to I. seychellarum could be arranged in descending order as follows: Fagrikalan >Alphonso-Naser >Baladi > Hendi >Dabsha. The essential oils of Fagrikalan and Dabsha mango cvs. leaves were determined by hydrodistillation and analyzed by GC-MS. A total of 38 components of the essential oil were identified. The insecticidal or repellent activities of some essential oils of the high susceptible Fagrikalan cv. and the completely tolerable Dabsha cv. against I. seychellarum nymphs revealed that, the chemical composition of essential oils plays an important role in this concern. This hypothesis was confirmed by the results of toxicity and repellent activities of the pure major compounds limonene, β- caryophyllene, and α-pinene of Dabsha cv. and the attraction effect of the high quantity of β–ocimene in Fagrikalan cv. against I. seychellarum nymphs.