780 LIGHT AND LIFE 



an array of gray cards of all shades from black to white. Kiihn (35) 

 performed similar training experiments with monochromatic lights 

 and demonstrated that near ultraviolet and blue-green lights also 

 seemed to be distinct colors for bees. Subsequently Hertz (29) pre- 

 sented evidence that blue-green and near ultraviolet are complemen- 

 tary colors for bees. Bertholf (4) also reported success in training 

 bees to different wavelengths. The difficult art of training bees to 

 reveal their sensory capacities has most recently been extended by 

 Daumer (9) . Daumer achieved a finer control of the wavelength and 

 intensity of stimulus than earlier workers and tested the ability of 

 bees to discriminate monochromatic lights and known mixtures of 

 monochromatic lights. 



The following picture of the color vision system of the bee unfolds 

 from these experiments. The spectrum visible to the honeybee extends 

 from about 300 m^a in the ultraviolet to at least 650 m^u, in the 

 red. Beyond these limits sensitivity decreases, but between these wave- 

 lengths there exists the capacity to distinguish colors. For a time it 

 was thought that bees could discriminate only four colors (see 17) . 

 Daumer confirmed that there are four spectral regions which bees 

 distinguish with great reliability — near ultraviolet (300-400 m/x) , 

 blue-violet (400-480 m,^) , blue-green (480-500 m/^) , and green-yellow- 

 red (500-650 m/x) — but he also showed that bees can discriminate 

 between wavelengths within these regions, although with somewhat 

 less precision. 



Daumer has also reported a series of experiments with honeybees 

 that are closely analogous to the color-matching experiments en- 

 countered in psychophysics. Bees were trained to alight on a feeding 

 dish illuminated from beneath. After a period of training the bees 

 were confronted with a pair of feeding dishes, one illuminated by 

 the training color and the other by a mixture of monochromatic 

 lights. The mixture of wavelengths at the test dish was varied (keep- 

 ing the total energy constant and equal to the training light) , and 

 when the bees went with equal frequency to the two dishes, the test 

 and training lights were considered to be equivalent. 



White light for the bee must include some ultraviolet; bees easily 

 distinguished a training light which was "bee-white" (the full spec- 

 trum of a xenon arc) from a white test light from which the ultra- 

 violet had been filtered. Equivalence was obtained, however, by 

 adding an appropriate amount of monochromatic 360 xn^i to the test 

 light. The important features of an experiment such as this are most 

 easily sunmiarized by a statement of colorimetric equivalence: 



