Fine colour discrimination requires differential conditioning in bumblebees

Accurate recognition requires that visual systems must be able to discriminate between target and distractor stimuli. Flowers are learned and recognised by bees using visual cues including colour and shape. We investigated whether bees were able to learn to discriminate between colours differently depending upon absolute or differential conditioning. For absolute conditioning bees were rewarded with sucrose solution for visits to target flowers. When distractor stimuli were subsequently presented, a high level of discrimination was observed if there was a perceptually large colour distance separating distractors and targets, but for a perceptually small colour distance the bees generalised and did not discriminate between stimuli. When provided with differential conditioning where both target and distractors were present, the bees learnt to discriminate stimuli separated by a perceptually small colour distance. This shows that for bees to learn fine colour discrimination tasks it is important to use differential conditioning. The findings are discussed within the context of the necessity for plants to produce distinctive flower colours.