CLASSICAL-CONDITIONING REVEALS DISCRIMINATION OF SALT TASTE QUALITY IN THE BLOWFLY CALLIPHORA-VICINA

Blowflies Calliphora vicina were trained to discriminate between two salt stimuli applied to their labellar taste organ, using a classical conditioning procedure modified after Nelson (1971). In Experiment 1, flies were trained to discriminate between concentrations of NaCl (Fig. 5). From this, the differential threshold (DT) was estimated to be 0.22 log units. The actual perceptual DT was argued to be above 0.05 log units, on the basis of electrophysiological data. In Experiment 2, flies were trained to discriminate various concentrations of LiCl, KCl, and NH4Cl from l M NaCl (Fig. 7). Curves of 'conditioning index' (CI) vs. concentration are trough-shaped with a distinct 'floori' well above zero, extending to each side of the 'iso-salt point'. The order of saltiness found was: LiCl<NaCl<KC1≦NH4C1. Within the concentration range of the floor, discrimination is based solely on taste quality differences, saltiness being an additional cue outside this range. Rate of learning (RI) was independent of concentration, but differed between salts. This suggests that the different taste qualities of the salts are differently aversive to the fly, in the order: NaCl<NH4Cl<KCl< LiCl. Female flies learned more slowly but better than males did. No effect of age was detected. Responsiveness was low and learning inconsistent (Fig. 4). It was argued that this is due to the poor learning ability of Diptera in general, rather than to the conditioning procedure or stimuli used. © 1979 Springer-Verlag.