THE ATTRACTION OF DIPTERA TO AMMONIA. 



By C. H. Richardson, 



Xew Jersey Agricultural College Experiment Station. 



During the course of experiments on the responses of the 

 house-fly to certain chemical compounds, data were gathered 

 concerning the reactions of some other species that entered the 

 traps with more or less regularity. It is the purpose of this 

 article to give the results of these experiments and to include 

 brief summaries of the literature concerning the olfactory 

 tropisms of insects. 



It has long been recognized that the olfactory organs of 

 insects are of primary importance in the search for food and for 

 breeding places, in the assembling of the sexes, and in the 

 reactions to certain repulsive smelling substances. The experi- 

 mental study of these responses to environmental odors, neglected 

 by entomologists in the past, has recently awakened an interest 

 which promises important results. 



Tragardh (1913) and Imms (1914) have published in England 

 valuable resumes of the literature touching upon this subject, 

 but I believe no fairly comprehensive bibliography has yet 

 been placed before American students. 



One of the earliest contributions to odor responses was 

 made by Barrows (1907) on the pomace-fly, Drosophila ampelo- 

 phila Loew. It was found that the flies responded positively 

 to aqueous solutions of amyl alcohol, ethyl alcohol, acetic acid, 

 lactic acid, and acetic ether. When acetic ether .was added to 

 acetic acid or ethyl alcohol, more flies were captured than when 

 acetic acid or ethyl alcohol was used alone. A similar phenom- 

 enon was observed when isobutyl acetate or methyl acetate 

 was mixed with ten per cent ethyl alcohol or when acetic, 

 butyric or valerianic acid was added to ethyl alcohol. The 

 strong mineral acids, nitric and hydrochloric, were very repellent. 

 A solution containing two and one-half per cent, of ethyl 

 alcohol and five-eighths per cent, of acetic acid called forth the 

 greatest number of positive reactions. Ethyl alcohol and acetic 

 acid are found in cider vinegar, fermented cider and California 

 sherry in jDercentages close to those which induced maximum 



408 



