Sensitivity of antennal gustatory receptor neurones to aphid honeydew sugars in the carabid Anchomenus dorsalis

Using electrophysiology, the stimulating effect of 13 sugars and three sugar alcohols (each at a concentration of 100 mm ) to antennal gustatory receptor neurones (GRNs) is tested in the carabid beetle Anchomenus dorsalis (Pontoppidan, 1763) (Coleoptera, Carabidae). Maltose, sucrose, glucose and raffinose are the most stimulating sugars for the sugar‐sensitive neurone (SuN), evoking 6.7–18.6 spikes s^?1 in fed insects, whereas the others had little or no effect. The firing rate of the antennal GRNs is not affected by any of the tested sugar alcohols, dulcitol, inositol and sorbitol. Additionally, concentration/response curves for sucrose and maltose are obtained in the range 0.01–100 mm . The responses of beetles starved for 96 h to this range of sucrose are two‐ to three‐fold higher compared with those of fed beetles. The presence of a terminal α‐glucose unit is an important feature of the molecular structure determining the stimulating properties of the two disaccharides, maltose and sucrose, as well as glucose. The other monosaccharide unit of the molecule is also of great importance in determining the stimulating properties of various disaccharides. The sensitivity of the SuN to the four most prevalent aphid honeydew sugars suggests that A. dorsalis uses these chemicals as sensory cues when searching for aphids as prey.