AND ITS SIGNIFICANCE FOR ECONOMIC ENTOMOLOGY. 117 



the females react with a positive chemotropism, and with which a kind of trap 

 might be prepared. 



In reality such methods have for a long time been practically utilised without 

 the theoretical foundation of the idea being understood. If, for example, we lay 

 out pieces of freshly pulled bark to act as traps for catching the pine weevil, or 

 make use of trap trees for bark-beetles, we are utilising in reality the specilie 

 chemotropism of the animals. 



But in no instance has as yet an attempt been made to ascertain what definite 

 organic combination in one plant or another chemotropically influences a certain 

 insect ; still less has an attempt been made to produce the same synthetically and 

 make practical use of it. 



In my opinion, however, the investigations of VerschafFelt, Dewitz, and 

 Howlett, if regarded in the light of the researches of physiologists into chemo- 

 tropism, are of an importance which cannot be overestimated, and will guide 

 practical entomology into new lines. Intimate co-operation between vegetable 

 chemistry and entomology in these questions will surely provide us with good 

 weapons in our fight with many insects, against which we are at present 

 absolutely helpless. 



Bibliography. 



1. Dewitz, J. The bearing of physiology on economic entomology. — Bull, of 



Ent. Research, vol. iii, pp. 343-354. London, 1912. 



2. Verschaffelt, Ed. The cause determining the selection of food in some 



herbivorous insects. — Konink. Akad. van Wetenschappen te Amsterdam, 

 Proc. of the Section of Sciences, vol. xiii, part 1, pp. 536-542. 

 Amsterdam, 1910. 



3. Howlett, F. M. The effect of oil of citronella on two species of Dacus. — 



Trans. Ent. Soc. London, 1912, pp. 442-448. 



