SEMIOCHEMICALS MEDIATING SPACING BEHAVIOR OF BIRD CHERRY-OAT APHID, RHOPALOSIPHUM-PADI FEEDING ON CEREALS

Olfactometry using an apterous individual of Rhopalosiphum padi (L.) s howed an arresting effect by volatiles from a wheat seedling and a rep ellent effect by volatiles from a wheat seedling infested with aphids at a high population density (ca. 9 aphids/cm(2)). Four compounds, 6-m ethyl-5-hepten-2-one, (-)- and (+)-6-methyl-5-hepten-2-ol, and 2-tride canone, were identified by CC-MS in air entrainments from the wheat se edlings with high aphid density but not from the wheat seedlings alone . The mixture of the four compounds in the natural proportion countera cted the attractivity of the volatiles from the intact uninfested whea t seedling. The likely role of these compounds in the spacing behavior of this aphid species, when present in high densities on wheat, is di scussed.