Fig. 4. Effects of different periods of exposure (6, 12, 24 or 48 h) to the control (A–C) or salicin (D–F) diet on the ingestive responses of caterpillars to the salicin diet. We used a 157 mmol kg^–1 concentration of salicin in both the exposure diet and the diet used to evaluate ingestive responsiveness. We calculated three ingestive parameters across each 2 min biting test: total intake, total number of bites and bite size. We tested all caterpillars both before (open columns) and after (filled columns) exposure to the control or salicin diet. Each caterpillar was exposed either to the control or to the salicin diet over one of the four exposure periods. We made paired comparisons between the ingestive response of caterpillars to the salicin diet before and after an exposure period, separately for each ingestive measure and exposure diet, using the Wilcoxon matched-pairs signed-rank test (*P0.0125). The number of caterpillars tested at each exposure period ranged between 19 and 23 for those exposed to the control diet and between 18 and 27 for those exposed to the salicin diet. All values are median ± median absolute deviation.