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Proportion of purple-pollen plants Bombus impatiens foragers visited first during the training sessions (T1–T4) and the testing session (Test). In training sessions, plants with purple pollen were rewarding and those with white pollen were not. In the test session, both colour morphs were non-rewarding. Asterisks indicate significant overvisiting of purple-pollen plants. Error bars represent the binomial 95 % confidence interval. *P < 0.05. **P < 0.01.
