Differential electrophysiological responses of wingless and winged forms of three non-host-alternating aphids to plant volatile compounds

From spring to autumn, aphids produce two types of asexual morphs: wingless and winged. Olfactory cues are often utilized by the winged morph in long-distance host plant selection, and by the wingless morph in short-range host plant location. Electroantennogram (EAG) responses to a range of plant volatiles were recorded from wingless and winged forms of the English grain aphid Sitobion avenae, greenbug Schizaphis graminum, and pea aphid Acyrthosiphon pisum. The response patterns of the three aphid species were similar, although some variations did occur. (E)-2-Hexenal elicited the largest EAG responses in both asexual forms (i.e., wingless and winged) of the three species. In general, green leaf volatiles and benzaldehyde produced relatively large EAGs. The winged form was more responsive than the wingless form to all the plant volatile compounds tested but 4-ethylbenzaldehyde for S. graminum, and hexanal and benzyl acetate for A. pisum. This study indicates that both forms of S. avenae, S. graminum, and A. pisum are able to detect various volatile compounds, and generally higher EAG response in winged forms suggest that they have a more responsive olfactory system than wingless forms, and are better-adapted for switching host plants under unfavorable environmental conditions.