ULTRA-VIOLET RAYS 121 



the orange, green and ultra-violet. Rays of a wavelength longer 

 than 630 /x/x were not visited at all. By raising the energy of a 

 less effective colour its stimulatory influence could be made equal 

 to that of a more effective colour. Sander further determined that 

 with different wavelengths the effects do not increase in the same 

 degree with the energy. The increase proved to be relatively 

 slow with the green rays and faster near the ends of the spectrum. 

 It thus appeared that the effects of light of different wavelengths 

 of equal energy may be very different for different amounts of 

 absolute energy. Thus it may be that the effect of green is 

 greatest in very low and that of ultra-violet in very high intensity. 



A relatively strong stimulatory effect of ultra-violet has been 

 observed by Peterson and Heussler (1928) in their experiments 

 on the photic responses of the Oriental Peach Moth (Laspeyresia 

 lyiolesta) and the Codling Moth (Cydia pomonella). Bertholf 

 (1931) also obtained a strong response to ultra-violet in the case 

 of both Drosophila and the hive bee. In the case of the last- 

 named insect he found that there are two zones of maximum 

 stimulative efficiency — one in the yellow-green at wavelength 

 553 /A/x and the other in the ultra-violet at 365 /xjla — the latter 

 being about four and one-half times as great as the former. In 

 view of the work of Sander, which stresses the unequal increase of 

 effect in different wavelengths, it is possible that Bertholf's con- 

 clusions may require modification. Bertholf, it may be added, 

 used lights of unequal energies and determined the relative effect 

 of equal energies by calculation. It is noteworthy that Priebatsch 

 (1933) found that the relative responses to different wavelengths 

 alter when the amount of energy is altered. With Carausius 

 rrwrosus it was found that this insect becomes black when resting 

 on a black background and becomes darker in proportion to the 

 amount of illumination. The effect, however, does not depend 

 on the energy alone. If monochromatic light of equal and 

 relatively high energy is used the effect is most pronounced in 

 ultra-violet light, whereas with weak illumination the effect of 

 green is the most pronounced. 



General Reflex Behaviour to Light. The responses of insects 

 to rays of specific colours have already been discussed, and there 



