Responsiveness of antennal taste hairs of the apterygotan insect, Thermobia domestica (Zygentoma); an electrophysiological investigation

Antennal taste hairs of Thermobia domestica were investigated by a modified tip recording technique. They are sensitive to aqueous salt solutions but do not show the characteristic features of a water and a salt receptor cell. Sucrose and fructose stimulated approximately half of the tested hairs. As revealed by spike amplitude histograms, in most cases two sense cells responded. Proline stimulated the hairs with a threshold concentration of about 2 mM. Again, in most cases, two sense cells responded. In relation to sucrose the major sensitivities to both fructose and proline were not found in clearly defined receptor cells as in flies, but were realized in different cells of either a higher or smaller spike amplitude. This suggests, that the number of specific binding sites varies among the receptor cells from one taste hair to the other. As in cockroaches, but unlike flies, spike series are mainly generated in the apical dendritic segments. It is suggested that these features of the sense cells in thermobian taste hairs represent a primitive condition in relation to the specification of taste hairs cells in higher insect taxa