The main insect pests inhabiting onion plants during the two seasons at Mansoura region were Thrips tabaci Lind.(36.3 and 36.9%), Aphis gossypii Glov. (28.7 and 28.5%), Eumerus amoenus Loew. (19.3 and 18.0%), Empoasca lybica de Berg. (11.1 and 11.8%) and Liriomyza trifolii Burgess (2.4 and 2.1%) in 2007/08 and 2008/09 seasons, respectively. On the other hand, the main insect pests inhabiting onion plants with low occurrence were Nezara viridula (0.4 and 0.4%), Bemisia tabaci (0.4 and 0.6%), Spodoptera littoralis (0.2 and 0.4%) and Cryptoblabes gnidiella (0.3 and 0.5%) during the two successive seasons, respectively. The main predators inhabiting onion plants and associated with the insect pests infesting this crop during the two successive seasons were the coccinellid Coccinella undecimpunctata (31.7 and 17.0%) , Coccinella septempunctata (32.3 and 38.7%), Cydonia vicina nilotica (19.2 and 28.7%) and the chrysopid, Chrysoperla carnea (16.8 and 15.6%) during 2007/08 and 2008/09 seasons, respectively. The maximum number of T. tabaci nymphs by using direct count method were 785 and 675 nymphs/ 10 plants in the second week of April 2008 and in the first week of April 2009 in the two successive seasons, respectively. On the other hand, the maximum number of T. tabaci adults by using direct count method were 100 and 68 individuals/ 10 plants in the fourth week of March 2008 and in the second week of March 2009 in the two seasons, respectively. The average number of T. tabaci nymphs were 297.2 ± 82.2 nymphs/ 10 plants during the first season 2007/08 and 249.9 ± 80.9 nymphs/ 10 plants during the second season 2008/09, while the average number of T. tabaci adults were 41.1± 9.8 and 30.2± 8.9 individuals / 10 plants during two seasons, respectively. Moreover, by using sticky trap method, the maximum number of T. tabaci adults were 218 and 200 individuals/trap in the first week of March 2008 and in the second week of April 2009 in the two seasons, respectively. The average number of T. tabaci adults were 112.0 ± 14.6 and 92.7 ± 21.2 individuals/ trap during the two seasons, respectively.