DETECTION OF COLORED STIMULI BY HONEYBEES - MINIMUM VISUAL ANGLES ANDRECEPTOR-SPECIFIC CONTRASTS

Honeybees Apis mellifera were trained to distinguish between the prese nce and the absence of a rewarded coloured spot, presented on a vertic al, achromatic plane in a Y-maze, They were subsequently tested with d ifferent subtended visual angles of that spot, generated by different disk diameters and different distances from the decision point in the device. Bees were trained easily to detect bee-chromatic colours, but not an achromatic one. Chromatic contrast was not the only parameter a llowing learning and, therefore, detection: alpha(min), the subtended visual angle at which the bees detect a given stimulus with a probabil ity P-o = 0.6, was 5 degrees for stimuli presenting both chromatic con trast and contrast for the green photoreceptors [i.e. excitation diffe rence in the green photoreceptors, between target and background (gree n contrast)], and 15 degrees for stimuli presenting chromatic but no g reen contrast. Our results suggest that green contrast can be utilized for target detection if target recognition has been established by me ans of the colour vision system. The green-contrast signal would be us ed as a far-distance signal for flower detection. This signal would al ways be detected before chromatic contrast during an approach flight a nd would be learned in compound with chromatic contrast, in a facilita tion-like process.