The electrophysiological responses of sensilla on the tibia of Schistocerca americana (Drury) to six compounds were examined. All the compounds were shown to cause feeding deterrence at high concentrations. Nicotine hydrogen tartrate, quinine, hordenine (all alkaloids) and salicin (a phenolic glycoside) all stimulated one cell in each sensillum. This was shown by differential adaptation experiments to be the same cell. In some sensilla this cell also responded to linamarin (a cyanogenic glycoside). Earlier work had shown that the activity of this cell was correlated with feeding deterrence. However, canavanine (a nonprotein amino acid) did not stimulate this cell, although it caused feeding deterrence. All the compounds, except salicin, produced a marked depression in the activity of cells responding to sucrose, and at higher concentrations of the compounds this inhibition was almost complete.
The activity of the deterrent cell and inhibition of the activity of sucrose-sensitive cells appear to act together to produce the behavioural effects of most chemicals, but canavanine appears to act only by suppressing the activity of other cells and salicin primarily through activity of the deterrent cell. In addition, quinine disrupts the activity of all the cells and in its presence the deterrent cell adapts very slowly so that the message signalling deterrence is sustained.
At low concentrations, salicin, and probably hordenine, increased the duration of feeding. In the case of hordenine this was due to an increase in the firing rate of sucrose-sensitive neurones; with salicin the increase was associated with a high threshold of response and a rapid rate of adaptation of the deterrent cell.
Thus, similar behavioural effects are produced by a variety of sensory phenomena with each compound acting in a slightly different manner from the others.