The relation between the intensity of light and the preference to different wavelengths in Musca domestica and Lucilia sp.

The phototactic choice of some pairs of colored lights by Musca domestica and Lucilia sp. after a rise in intensity of the non-preferred light in spontaneous responses was studied. In the range of spectrum where no preference in spontaneous responses is noted, the brighter light was chosen after its intensity was increased. It is difficult or even impossible to change the preferences of insects to these lights which are well discriminated in spontaneous reactions after increasing the intensity of the less attractive light.