Natural abundance of the ectoparasitoid Diglyphus isaea Walker was studied in four tomato greenhouses at Sakha, Mehalla Al-Kobra, and Metobus. The parasitoid showed low populations in March, then developed good populations that kept the populations of the  serpentine leafminer, Liriomyza trifolii at low densities till the end of the season in all studied greenhouses. D. isaea recorded two peaks of abundance in three of the  greenhouses, the highest peak recorded  21, 36, 28 and 31 individuals/ 50infested leaflets in greenhouses 1, 2, 3 and 4, respectively . The highest average numbers occurred in April in all greenhouses recording 18 ± 2.9, 24.3 ± 8.3, 23.0 ± 5.2 and 26.0 ± 5.2 individuals/ 50infested leaflets in greenhouses 1,2,3 and 4 ,respectively. On the other hand, the percentage of parasitism ranged between 17.8 ± 0.9 and 47.3 ± 1.3% recording its highest numbers in May in greenhouse 1 (43.3 ± 5.3%), and in April in  greenhouses,2,3 and 4 recording  46.4 ± 5.1 , 43.6 ± 2.3 and  47.3 ±1.3% , respectively. The percentage of killed larvae according to host-feeding recorded its highest monthly average numbers in May in greenhouses 1, 2 and 3 (43.5 ± 5.3 , 29.0 ± 9.2 and 24.0 ± 7.3% respectively) and in June in greenhouse 4 recording  30.6 ± 6.4% .