Reactions of the Pomace Fly to Odorous Siihstarices 519 



quent to those under discussion, however, showed that the flies did 

 enter or attempted to enter traps which contained acetic ether in 

 aqueous solution, so that it is possible that under other conditions 

 the flies might be positive to some of the substances to which in 

 these preliminary experiments they seemed not to be. 



In Experiment 2 one trap was charged with 4 per cent acetic acid 

 and another trap with 4 per cent acetic acid containing a small 

 amount of acetic ether. The number of flies found in the trap which 

 contained the mixture of acid and ether gready exceeded that in the 

 trap charged with acid only. A similar contrast was observed in 

 Experiment 3. This increase of flies in the trap containing the 

 mixture is evidently due to the acetic ether. A similar phenomenon 

 was seen when to 10 per cent ethyl alcohol, a small amount of 

 acetic ether, isobutyl acetate, or methyl acetate was added (Experi- 

 ments 3 and 7). Isoamyl acetate may possibly also be classed 

 with these substances, though the results of Experiments 4 and 7 

 do not show an entire agreement in this respect. An increase was 

 also obtained when acetic or butyric acids were added in small 

 amounts to the alcohol. This property may be slightly shared by 

 valerianic acid and possibly by osmic acid, but it is certainly not a 

 characteristic of hydrochloric and nitric acids which seem to be 

 strongly repellent (Experiments 4 and 8). 



All the organic substances tested in these preliminary experi- 

 ments are found in fermenting fruits and the test conditions which 

 gave the highest positive numerical results are probably those 

 which simulated most closely the natural optimum conditions. 



2 Experiments luith Alcohol, Acetic Acid and Acetic Ether 



As a more complete analysis of the eflPect of some of the odorous 

 substances used in the preliminary experiments was desirable, 

 it was decided to test more fully acetic acid, ethyl alcohol and 

 acetic ether. These were chosen because they are commonly 

 found in fermenting fruit, the first two in quite large quantities 

 and the third in traces. To make the tests more accurate, a new 

 piece of apparatus was constructed in which two traps were so 

 placed in the sides of a leaden trough that each fly as it passed 



