Quantification of electroantennogram responses of the primary rhinaria of Acyrthosiphon pisum (Harris) to C₄-C₈ primary alcohols and aldehydes

Electroantennograms (EAGs) of the distal and proximal primary rhinaria (DPR and PPR, respectively) were recorded from excised antennae of alate virginoparous pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae). Primary unsaturated alcohols and aldehydes with varying carbon length (C₄-C₈) were used as volatile stimuli. EAGs were recorded for a series of source concentrations from the DPR and PPR separately through the use of sectional electroantennography. A logistic equation was fitted to the source concentration-response data. Differences in relative EAG response of the DPR and PPR to the alcohols and aldehydes were analyzed by deriving five parameters from this logistic equation. These parameters relate to particular characteristics of sigmoid curves: the saturation (maximum) EAG response (R_s), the concentration for which the relative EAG response is 1/2R_s (CR₅₀), the stimulus response range (SR_0.9), the threshold concentration (CR₁), and the EAG response area (A_R). Of these parameters, the EAG response area showed the largest separation between EAG responses of the DPR and PPR to the two homologous groups and between compounds with varying carbon chain lengths. The DPR was significantly more responsive to alcohols than to aldehydes, while the reverse was true for the PPR, indicating a basic difference between the two primary rhinaria. The highest overall responses were elicited by 1-hexanol, hexanal, and heptanal.