EN
The purpose of performed analyses was to study the impact of Rhopalosiphum padi L. infestation on the level of ribonucleolytic activity in bird cherry leaves during three consecutive vegetation seasons (2003–2005). It was shown that feeding of the bird cherry-oat aphid on P. padus leaves stimulated the activity of acid and alkaline ribonucleases when compared to control (without aphids). Furthermore, the highest rise in activity of both groups of RNases was recorded during increasing and maximal density of aphid population on its primary host shoots.