270 CJteniofropic Respoii^en of Inaectn 



world and yet we scarcely possess any knowledge as to how they act. 

 Since 1787, when the Abbe Roberjot first discovered the method of 

 destroying the vine moth {Sparganothis pilleriana) by means of light, 

 the application of this method has developed rapidly, and there are now 

 in existence ingenious traps, elaborate lanterns and even expensive 

 and complicated electric installations; but strange as it may seem, it 

 was not until 1904 that the study of the effects of light of different 

 colours, in attracting insects, was first taken up by Perraud. Even to 

 this day our knowledge of the physical side of the subject is far from 

 adequate; much research is also needed with regard to the influence of 

 meteorological conditions, and we know comparatively little concerning 

 the proportion of the sexes of the insects attracted. Chemotropism has 

 shared no better fate, and we are largely in the dark as to the influence 

 of the various constituents of those baits extensively used by economic 

 entomologists. Molasses forms one of the most important ingredients, 

 but we are totally ignorant as to which constituent (or constituents) of 

 this complex substance exercises chemotropic properties. Dewitz (1912), 

 Tragardh (1913) and Imms (1914) have emphasised the need for physio- 

 logical research in applied entomology, but such research they insist 

 must be carried on with a broader outlook than that of modern applied 

 entomologists. The possibilities that the investigation of chemotropism 

 offers, both as regards the application of results achieved and the advance- 

 ment of scientific knowledge, can be well appreciated by reference to the 

 work of Verschaft"elt(1910), Howlett (1912, 1914, 1915), Barrows (1907), 

 Richardson (1916, 1917) and others. There is hardly any doubt that one 

 of the most promising aspects of applied entomology lies along these lines 

 and, as will be pointed out on a later page, in chemotropism we should 

 seek for new and effective measures for combating insect enemies. The 

 control of the house-fly supports this contention, but wo are only at the 

 threshold of an extensive line of investigation. 



The present paper only embodies observations of an essentially 

 preliminary nature and were carried out by M. A. H usain at the suggestion 

 of the senior author (A. D. Imms); the interpretation of the results and 

 the writing of tliis article is a conjoint production. Delay has been in- 

 evitable in the preparation of this paper owing to one author being 

 transferred to India, while the other was located at the Rothamsted 

 Experimental Station, Har])enden. The necessary laboratory work was 

 conducted in the Department of Agricultural Entomology, Manchester 

 University. We are greatly indebted to Messrs C. G. Lamb, P. H. Grim- 

 shaw and H. Bury for help iu identifying numerous specimens of Di|)tera. 



