Fig. 3. Conditioned responses from two different groups of animals that received different concentrations of scented (5 µl l^-1) sucrose solution during trophallaxis (either 0.5 mol l^-1 or 1.8 mol l^-1). A control group of animals (C) received unscented 0.5 mol l^-1 sucrose solution. (A) General percentage of proboscis extensions (%PE_G). Letters indicate statistical differences among the different odour concentrations (G-test, ^***P<0.001; see Results for details): the results of two groups that do not differ significantly are denoted by the same letter. (B) Percentage of proboscis extensions (%PE) corresponding to the first (%PE₁, white bars), second (%PE₂, grey bars) and third tests (%PE₃, black bars). Animals were tested 21, 27 and 46 h following trophallaxis in a cumulative fashion. The number of animals is given in parentheses. In B, differences in the sample size within a given group are due to differences in mortality and US responsiveness prior to the tests.