114 THE SENSE ORGANS AND REFLEX BEHAVIOUR 



He also found that bees are capable of being conditioned to 

 yellow, but that they failed to discriminate between that colour 

 and orange or yellow-green : similarly, bees conditioned to blue 

 turned indiscriminately to violet or purple. Von Frisch failed to 

 train bees to visit any particular shade of grey in preference to 

 any other shade. This important result affords a strong argument 

 against the objection that a highly developed response, on the 

 part of the insects, to different degrees of brightness might account 

 for their supposed differential colour responses. Von Frisch's 

 conclusions proved to be sound when training experiments with 

 bees were repeated subsequently, by using monochromatic light, 

 by Kiihn (1927) in Gottingen. In addition to the two main 

 colours (yellow and blue), which von Frisch found to be responded 

 to by the bee, Kuhn was able to include blue-green and ultra- 

 violet. It appears, therefore, that four regions of the spectrum 

 exercise separate and definite stimulus qualities with respect to 

 the bee, i.e., 650 i to 500 /x/x, 500 to 480 /x/x, 480 to 400 /x/x, 400 to 

 313 /x/Lt. By training insects along lines very similar to those 

 adopted by von Frisch, Knoll (1921) found that the Humming 

 Bird Moth (Macroglossa stellatarum) showed good capacity for 

 differentiating between yellow and blue, but was likewise unable 

 to discriminate between red and black. It must not, however, 

 be assumed that all insects are red blind, since Kugler (1930) 

 succeeded in training Bombus to a pure red Hering paper and Use 

 (1928) found that in Pieris and related butterflies responses are 

 mainly to red and to purple papers, while in the case of Vanessa 

 they were to yellow and to violet. Both Knoll (1921) and Use 

 (1928) state that a predilection for definite colours is inborn in 

 butterflies since the latter visited certain coloured but inodorous 

 surfaces, in preference to all shades of brightness, just after 

 emergence from pupa?. 



Further important experiments, bearing upon colour vision in 

 insects, have been carried out by means of a screen which revolves 

 round a circular horizontal platform covered with white paper 



1 According to Bertholf (1931) the upper limit for the bee extends to at 

 least wavelength 677 ^i^ in the red end of the spectrum ; a difference in the 

 intensity of the spectral light used probably explains why these results do not 

 conform with those obtained by Kiihn. 



