Mat 12, 1922] 



SCIENCE 



519 



THE REACTION OF DROSOPHILA TO 

 ULTRAVIOLET 



Although there is no unanimity of opinion 

 as to the ability of insects to distinguish colors 

 in the sense that humans do, it is fairly well 

 established that the tendency is for them to 

 react most strongly to wave-lengths in the 

 violet end of our visible spectrum. This sug- 

 gests the possibility that insects may be sensi- 

 tive to ultraviolet, to which the human eye is 

 relatively insensitive except indirectly by 

 fluorescence in the cornea. The possibility is 

 of interest in connection with the general prob- 

 lem of the biological relations between flowers 

 and insects, for flowers may be "ultraviolet" as 

 well as red, yellow, and so on. A committee of 

 the National Research Council is planning to 

 do fleld-work on this problem during the coming 

 summer and it was thought that the following 

 experiments might give useful preliminary 

 information. They were made with the as- 

 sistance of Mr. Ware Cattell. 



Drosophila melanogaster exhibits a strong 

 tendency to move toward the source of light. 

 A large number of these flies were placed in 

 a test tube about 30 cm. long and 2 cm. diam- 

 eter, the end being closed with a plug of cotton. 

 A strip of black paper was rolled around the 

 tube to protect from stray light. By slipping 

 the paper down from the end of the tube the 

 flies could be "concentrated" next to the cotton 

 plug. The paper was then replaced and the 

 tube placed horizontal with its rounded end 

 toward the spark from a 200 watt General 

 Electric ultraviolet generator. Between the 

 generator and the tube were placed four thick- 

 nesses, totaling about 1 cm., of Corning ultra- 

 violet glass, number G586A (old number 

 G55A62). After an exposure of 15 seconds 

 the flies were found to have congregated in the 

 end of the tube next to the source, showing 

 that they were strongly attracted by the ultra- 

 violet generated by the spark and transmitted 

 by the special glass. 



The transmission of this glass has been 

 measured by the Bureau of Standards (Tech- 

 nological paper Number 148: "The Ultraviolet 

 and Visible Transmission of Various Colored 

 Glasses"). A thickness of one centimeter 

 transmits about 70 per cent, of light in the 



neighborhood of 0.36; about 25 per cent, near 

 .34; but only 5 per cent, at 0.40. This glass 

 transmits also a small amount of red. The 

 flies, however, did not react when we used a 

 red glass which transmitted far more red than 

 G586A. 



To make a more accurate test, a quartz spec- 

 trograph was used to disperse the light from 

 the ultraviolet generator. Light of wave-length 

 greater than .39 was excluded by a strip of 

 black paper in the focal plane. As before, the 

 flies showed a very marked reaction when the 

 horizontal test was "pointed" toward the ultra- 

 violet source. 



This last result was, however, rendered some- 

 what doubtful by the fact that the quartz 

 lenses and the dispersing system scattered a 

 small amount of blue and violet light. This 

 scattered light was entirely eliminated, at least 

 so far as human vision is concerned, by inter- 

 posing a single thickness, 2.5 millimeters, of 

 G586A in the path of the light. But even then 

 the flies showed a marked reaction. The con- 

 clusion is that Drosophila melanogaster is more 

 sensitive to ultraviolet light than is the human 

 eye. 



The question may still be raised that these 

 phototropie reactions of Drosophila are due to 

 fluorescence of eye media, similar to that expe- 

 rienced by the human ej'e when exposed to 

 ultraviolet light. All that can be said at 

 present in this connection is that the intensity 

 was so low that we did not experience the visual 

 sensation characteristic of such fluorescence, 

 but the flies reacted promptly and definitely. 

 F. E. LuTZ, 



American Museum of Natural History 



F. K. RiCHTMYEE, 



Cornell University 



THE AMERICAN ASSOCIATION FOR 

 THE ADVANCEMENT OF SCIENCE 

 SECTION A— MATHEMATICS AND ASSO- 

 CIATED SOCIETIES 



Section A of the American Association for 

 the Advancement of Science met in Room 8 

 of the Main Building of the University of 

 Toronto on Thursday afternoon, December 29, 

 1921, in joint session with the American 

 Mathematical Society and the Mathematical 



