How bees detect coloured targets using different regions of their compoundeyes

Honeybees Apis mellifera detect coloured targets presented to the frontal r egion of their compound eyes using their colour vision system at larger vis ual angles (alpha > 15 degrees), and an achromatic visual system based on t he long-wave photoreceptor type at smaller visual angles (5 degrees < alpha < 15 degrees). Here we examine the capability of the dorsal, ventral and f rontal regions of the eye for colour detection. The minimum visual angle al pha(min) at which the bees detect a stimulus providing both chromatic contr ast and receptor-specific contrasts to the three receptor types varies for the different regions of the eye: 7.1 +/- 0.5 degrees for the ventral regio n, 8.2 +/- 0.6 degrees for the dorsal region and 4.0 +/- 0.5 degrees for th e frontal region. Flight trajectories show that when the target was present ed in the horizontal plane, bees used only the ventral region of their eyes to make their choices. When the targets appeared dorsally, bees used the f rontodorsal region. This finding suggests that pure dorsal detection of col oured targets is difficult in this context. Furthermore, alpha(min) in the ventral plane depends on receptor-specific contrasts. The absence of S-rece ptor contrast does not affect the performance (alpha(min) = 5.9 +/- 0.5 deg rees), whilst the absence of M- and L-receptor contrast significantly impai rs the detection task. Minimal visual angles of 10.3 +/- 0.9 degrees and 17 .6 +/- 3 degrees, respectively, are obtained in these cases. Thus, as for m any visual tasks, the compound eye of the honeybee shows a regionalisation of colour detection that might be related to peripheral or central speciali sations.