The leaves of wheat infected by powdery mildew Erisiphe graminis var. tritici manifested repellent action against cereal aphids Rhopalosiphum padi and Sitobion avenae. Food (leaves) for aphids enriched in chemical components present in diseased leaves caused weaker reproduction of S. avenae and mortal i ty of R. pad i. It could be caused by post-infection increase of the level of monophenols and flavanoids in the leaves of wheat infected by powdery mildew (E. graminis var. tritici). These compounds increasing IAA-oxidase activity in plants can have a harmful influence on the cereal aphids.

The influence of cinnamic acid, 1-tryptophane, 3,4-dihydroxyphenylalanine, 2,4-dichlorophenol modifying IAA-oxidase activity and indoleacetic acid on the development and reproduction of cereal aphids in laboratory conditions was tested. We observed that IAA and Try stimulated the reproduction of cereal aphids whereas CA, DOPA and DCP decreased it.