The present investigation was carried out at Ismailia Governorate during 2010 and 2011 seasons to evaluate the seasonal activity of the parasitoids and predators associated with the mealy aphid Hyalopterus pruni population. During the study two parasitoid species belonging to Aphidius colemani Viereck and Aphidius picipes (Nees) and six predator species, Chrysoperla carnea Steph., Coccinella undecimpunctata L. Aphidoletes aphidimyza Rond., Syrphus corollae F. Cydonia vicinia nilotica Muls. and Scymnus interruptus Goeze. were recorded. The highest percentage of parasitism by the two parasitoids were recorded on the half of May (48.11%), during 2010, while in the second season 2011 was recorded in the last week of May (51.56%) with on average percentage of parasitism 20.77 and 18.03% during the two successive seasons respectively. Laboratory experiments were carried out to study some biological aspects of the main natural enemies associated with the mealy aphid. The obtained results indicated that the developmental period, as well as adult longevity of the parasitoid A. colemani, was affected by temperature and food. However, the developmental period decrease as temperature increase. Total developmental periods of A. colemani ranged between 9.2-37.37 days, also the longevity was affected by temperature and food for A. colemani. Studying the behavior of the same parasitoid at varying host densities showed a decrease of leaf – arrival times and host arrival times with increasing of host density but number of stings and number of mummies increased with increase of host density. Statistical analysis showed that temperature and relative humidity were significant with some insects and insignificant with the others.