The bird cherry-oat aphid (Rhopalosiphum padi L.) development on primary host (Prunus padus L.) was studied in Poznan in 2007–2008. First fundatrices of R. padi were observed already on the bird cherry in March in both years. The largest condensation of population was observed in May. At the second decade of May numerous winged morphs were formed and spring migration into the secondary hosts started. Re-emigrants in September were observed and the oviparae and males in second decade of October gave birth. In spring observations fertilized eggs (from which aphids hatched) made up 89% and 81% respectively. The meeting of factors inducing the formation of individual morphs of R. padi and the deadlines of the migration on host-plants has a special meaning in the aspect of transfer of viruses by the anholocyclic forms of this species.