The present study was carried out at the experimental farm, faculty of Agriculture, Mansoura University during two seasons (2010 and 2011) to evaluate the host plant (blood orange, limon and mandarin) - scale insect, parlatoria. oleae (Colvee)interactions.               The olive scale, P. oleae Population exhibited three peaks of abundance on blood orange and limon orchards, while, it showed two peaks only on mandarin orchard.  The more favourable host for P.oleae was blood orange followed by Limon then mandarin. However, P. oleae female showed the highest fecundity on blood orange trees and the lowest on mandarin trees. The average number of offspring for p.oleae female was 35.4 ± 4.8, 30.9 ± 5.6 and 18.7 ± 4.2 / female on blood orange, Limon and mandarin leaves, respectively. Chemical analysis indicated that mandarin leaves had the highest percentage of total protein in comparison with limon and blood orange leaves. On the contrary, the pest exhibited the lowest reproductive rate and population density on mandarin leaves. So, volatile oils produced by the mandarin leaves may play a role in insect biology. Statistical analysis indicated that there was a positive correlation between the changes of total protein contents and those of P. oleae population density in all tested host plants.