Differential responses of galeal gustatory sensilla of the adult Colorado potato beetle, Leptinotarsa decemlineata (Say), to leaf saps from host and non‐host plants

ABSTRACT Responses of galeal sensilla of the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), to leaf sap from Solanum tuberosum and a number of other solanaceous and non‐solanaceous plants are described. A single cell responds vigorously to expressed sap from S.tuberosum , ‐and even to ten‐fold dilutions of expressed sap. The response is characterized by a high spike frequency, low phasic activity and a tonic phase which can last for tens of seconds. At 8 s following stimulus application the primary response is typically 50% of its original activity, indicating slow adaptation to the sap stimulus. The primary response varies little among multiple stimulations of single sensilla and among sensilla on the same animal. There is a secondary response to potato leaf sap from one or more cells which have low spike amplitudes. This is usually of much lower frequency than the response from the primary cell, and it is highly variable. The prominent and reproducible single cell response to potato sap may be an important component in signalling the presence of a host plant. This hypothesis is tested using saps from two other species of Solanum which are hosts, and several solanaceous and non‐solanaceous non‐hosts. Responses of galeal sensilla to the three host‐plants tested were qualitatively similar and reproducible while responses to the non‐hosts were highly variable and qualitatively different from responses to host saps. These results are interpreted and discussed in the context of a possible mechanism for chemosensory coding of complex stimuli in the insect/plant relationship. Analysis of the raw electrophysiological data required extensive use of a microcomputer and several programs were developed during the course of this study. The computer analyses are briefly described in the paper and additional information and copies of the programs are available from the authors.