﻿344 J. DEWITZ — THE BEARING OF PHYSIOLOGY 



written about it ; but hardly anyone has considered and been guided in his efforts 

 by wider scientific aspects. 



Surely it must strike one as strange indeed that the most varied sources of 

 light have been utilised without examining, on the one hand, the various lights 

 spectroscopically, as to their composition, and without studying, on the other 

 hand, the power of attraction of the various rays of light upon different insects. 

 T. Perraud 31 is apparently the only investigator who so far has entered into these 

 questions. He projected a large spectrum on a screen in a dark room and 

 observed the aggregation of the moths, Clysia ( Conchylis) ambiguella and Spargano- 

 this pilleriana, on the different colours of the spectrum. He found that the less 

 refractive colours of the spectrum, namely red to green, exercised by far the 

 strongest attraction. Some time ago also experiments were made in vineyards 

 at Saarburg (Saar, Germany), 17 with lamps provided with glass covers of 

 various colours. It was found that the lamps with green glass had attracted the 

 largest number of insects. These results also agree with the observations which 

 Hess 24 made with fishes, which clearly demonstrated that fish flock in largest 

 numbers to yellow-green colours of a spectrum thrown on the water. 



Again, it would be certainly a great advantage if the strength of the various 

 lights were exactly measured photometrically, in order to ascertain the optimum 

 degree of illumination for trapping insects. 



In connection herewith the study of the degrees of attraction which various 

 artificial lights exercise upon the sexes should prove of great interest and might 

 be useful for practical purposes. A number of experiments have already been 

 made in order to ascertain the sexual proportion of the insects caught, but so far 

 the figures resulting therefrom do not admit of formulating a fixed rule or 

 drawing definite conclusions. When at the Station de Pathol ogie Vegetale at 

 Villefranche (Rhone) of Mr. Vermorel, P carried out over a long period a series 

 of such experiments with acetylene lamps and obtained fairly definite results 

 regarding some insects. I ascertained that the percentage of the captured 

 females gradually increased from the Bombyctdae upwards to the Microlepi- 

 doptera ; further, that in my various experiments each of the groups appeared 

 to possess a tendency to furnish a fixed number of female victims. With 

 Bombyctdae the percentage of the females was 4, with Noctuidae 19, with 

 Geometridae 27, and with Tineina 39. Simultaneously I observed 

 that the percentage of females of Sparganothis pilleriana (Tineina), a pest of 

 the vine, which had been caught with acetylene lamps by Messrs. Vermorel and 

 Grastine, was 40, which is almost identical with the percentage of 39 ascertained 

 by me for Microlepidoptera in general. Laborde 25 found the same percentage 

 for the females of Clysia {Conchylis) ambiguella (Tineina). 



Moreover, in connection with insect trap-lanterns, it is probable that certain 

 changes in the physiological conditions of the individual insects or of the sexes 

 may take place which in turn may influence the number of individuals that may 

 be on the wing at any given time. What, for instance, may in this respect be 

 the effect of cold or of heat ? Or is the flight of the females diversely influenced 

 by the complete possession, or the partial or complete evacuation of the eggs ? 

 Such questions have already been put, but their practical study and solution 

 have so far never been seriously attempted. From observations made by 



