ELECTROANTENNOGRAM RESPONSES OF THE GRAIN APHIDS SITOBION-AVENAE (F) AND METOPOLOPHIUM-DIRHODUM (WALK) (HOM, APHIDIDAE) TO PLANT ODOR COMPONENTS

Electroantennogram responses (EAGs) to a range of plant volatiles were recorded from alate summer forms of the English grain aphid Sitobion avenae and the rose-grain aphid Metopolophium dirhodum. This bioassay screens for potential semiochemicals which are involved in host plant selection. EAGs of both species reveal pronounced receptivities of the antennal olfactory sensilla for the green leaf volatiles. In S. avena e (E)-2-hexenal and hexanal elicit larger responses than the correspon ding alcohols, whereas in M. dirhodum only the mono-unsaturated C6 ald ehyde produces larger EAGs than the alcohol. In the remaining group of plant volatiles benzaldehyde, benzyl acetate, 2-phenylethyl acetate, linalool, citronellal and beta-pinene elicit distinct EAGs from both s pecies. Structure-activity relationships are especially evident in the S. avenae olfactory responses. The response profiles of the aphid spe cies are similar, although species-specific traits occur.