Electroantennogram responses of aphid nymphs to plant volatiles

Abstract. Electroantennogram (EAG) responses of immature aphids were investigated for 30 plant volatile compounds in third‐ and fourth‐stadium nymphs of the black bean aphid, Aphis fabae . The nymphs were destined to develop into adult alate (winged) virginoparae. The EAG response profiles were similar to those previously reported in the adults. Among the compounds tested, hexanonitrile elicited the largest EAG responses in both nymphal stadia, corresponding to previously reported results with adults. Six‐carbon aliphatic compounds showed relatively higher EAG activities in the nymphs but, in contrast, ( E )‐2‐hexenal, benzaldehyde, α‐pinene and β‐pinene, and citronellal elicited relatively smaller EAG responses in nymphs than adults. Although overall EAG response profiles were similar between the third and the fourth stadia for the majority of the volatiles, four aldehyde compounds, hexanal ( E )‐2‐heptenal, 2‐hydroxybenzaldehyde and citronellal, showed relatively higher EAG activities in the third than in the fourth stadium. The present study indicates that aphid nymphs possess a functional olfactory receptor system before the antennae are fully developed morphologically and physiologically.