<p>The study was conducted during (2015/2016 and 2016/2017) on bread wheat cultivars: Sahel1, Seds4, Gemaza9, Giza168, and Misr2 in Plant Protec. Dept. farm, Fac. of Agric., Assiut Univ., Assiut, Egypt to determine the separate effect of some abiotic and biotic factors on the population dynamics of aphid species: <em>Mayzus persicae</em>; <em>Brivecoryne brassicae</em>; <em>Rhopalosiphum padi</em>, and onion thrips, <em>Thrips tabaci</em> Lindeman under drought and irrigation conditions. The considered abiotic factors: plant age, chlorophyll AB; climatic factors: Daily Maximum Temperature (DMxT), Daily Minimum Temperature (DMnT), Soil Daily Maximum Temperature (SMxT) and Soil Minimum Temperature (SMnT) at 3 to 5 cm depth from soil surface, beside the biotic factors which presented in natural enemies (N.E.) to clarify which cultivar is suitable to be planted under drought or irrigation conditions under free insecticides use for both pests with references to cultivars yields. The infestations of both pests started in February during 1^st season and January for 2^nd season in all replicates with a high mean numbers of pests on cultivars under irrigation conditions than drought conditions. The peaks of aphids recorded from the middle of the 2^nd month to the 3^rd month; and thrips in the 2^nd month to the half of 3^rd month from sampling date under both conditions. The most important factors regulated the fluctuation of pests under drought conditions were arranged according to their efficiency as (DMnT= 26.70), (DMxT= 16.91), and (N.E= 16.40); respectively out of (66.50 %). Under irrigation conditions,<em> </em>fluctuations were determined by the efficiency of (N.E.= 38.17), (Chlorophyll AB= 14.97), and plant age (9.96); respectively out of (83.19 %) with positive significant correlations on all selected cultivars. Top yields were gained from Giza186, Misr2, and Sahel1; respectively during seasons of the study under both conditions, except Gemeza9 under irrigation condition in 1^st season ranked the 3^rd yield.</p>