Fig. 1. The effect of US concentration on acquisition, retention and extinction of the conditioned PER, and the effect of time on retention and extinction in H. virescens. The proportion (%) of moths showing CR in each of the acquisition, retention and extinction trials is shown. (A) Average acquisition curves obtained in classical conditioning experiments with racemic linalool as CS and 2 mol l^–1 and 3 mol l^–1 sucrose as US. The letters NS indicate no significant between-group differences (Mann–Whitney test, P<0.05). (B) Retention in moths receiving 2 mol l^–1 or 3 mol l^–1 sucrose reward tested at different times after acquisition. Retention decreased significantly from 15 min to 48 h. N>31 in all retention groups. Different letters indicate significant between-group differences (Fisher's exact tests, P<0.0127). (C) Acquisition and extinction curves for the five retention times and the two sucrose concentrations. The extinction curves were obtained by stimulating with CS alone. No significant between-group differences were found, indicated by the letters NS (2 mol l^–1: Kruskal–Wallis test, P>0.05; 3 mol l^–1: Kruskal–Wallis test, P>0.05). (D) Extinction curves for moths tested after 15 min, 2 h, 8 h, 24 h or 48 h. Only moths showing CR at the first extinction test were included. Extinction was slower in the moths tested after 48 h. Different letters indicate significant between-group differences (Noether tests, P<0.0127).