Visual edge detection in the honeybee and its chromatic properties

Abstract

Free-flying bees were trained to collect a reward of sugar-water at one of several discs placed horizontally on a contrasting background. In sub­sequent tests the reward was removed and the behaviour of the bees was observed and recorded on video-tape while they landed on the experi­mental arrangement in search of the reward. The spatial distribution of the landings was analysed to measure the detectability of the discs and attractiveness of their boundaries, as com­pared to the interior regions. The results reveal that, while landing on figures, bees pay special attention to the edges. Even though the reward is placed at a randomly chosen location within the figure during training, the bees show a distinct preference for landing near the boundary of the figure. The bees’ preference for edges is restricted to figures with bound­aries that provide contrast to the green-sensitive receptors. When the boundaries contain no green contrast, the edge preference disappears. In this situation, landings continue to occur mainly within the figure, but they tend to be distributed randomly over its entire surface. Thus, whereas colour information can mediate the detection of objectsper se, the detection of edges, at least in the context of landing on a figure, is a colour-blind performance that is driven primarily by signals from the bee’s green-sensitive photoreceptors. This finding has interesting parallels in primate vision, where edge detection is also colour-blind. On the basis of these findings, we propose that edges provide cues that play an important role in guiding landing manouevres towards objects of interest, such as flowers.