The present investigations were oriented to elucidate the effect of some factors (biotic and abiotic) on the population of cereal aphid species infesting wheat plants at Assiut. Data obtained indicated that aphids appeared on wheat plants during the first half of January when the plants were in the tillering stage. The population attained a peak of abundance during last week of February when the plants were in the flowering stage, correlated with plant age 77 days. The disappearance of the aphids from the field was recorded during the end of March when the plants were in the ripening stage. The multiple regression analysis show that the eight selected variables (plant age, max. and min. temperature, max. and min. relative humidity, effective temperatures (day-degrees), predators and parasitoids) were together responsible for about 82% of the aphid populations during wheat growing season. Plant age seemed to be responsible for about 30.61 and 29.15% of the variability in the infestation with cereal aphid complex during 2014 and 2015, respectively. Plant age came in the first order with a relative efficiency of the total efficiency (8 variables). Natural enemies (parasitoids and predators) seemed to be responsible for about 17 and 8% during 2014 and 14.26 and 9.06% during 2015, season of the total efficiency. Rating sort of co-efficient of determination indicated that biotic factors came in the two and three degrees for 2014 and 2015 growing seasons. It was found that maximum air temperatures were found to be responsible for about 7.85 and 8.72% during 2014 and 2015 growing seasons of the variability of cereal aphids infesting wheat plants. The minimum relative humidity was found to be in the lowest degree.
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