Reactions of the Pomace Fly to Odorous Substances 527 

 ^ Experiments on the Directive Effects of Odorous Substances 



Having determined that these flies are chemotropic to fermenting 

 fruit, I turn to the second question, In what way does the fly find 

 its food ? 



To ascertain the accuracy of flight toward the food, experi- 

 ments were carried out in the following way. About one hundred 

 hungry flies were hberated in a large laboratory room. A few 

 minutes after their liberation a tumbler, freely exposed on the top 

 of a table and containing fermenting banana was opened. As the 

 hungry insects in flying through the room passed near the table 

 they eventually discovered the banana. When they were six or 

 more feet from the tumbler they showed a rather characteristic 



TABLE VII 



Amounts {in per cent) of acetic acid, and alcohol found in cider vinegar, fermented cider, and California 



Sherry {Leach 'o§) 



vibratory flight. Short rapid excursions were made through the air, 

 up and down, forward and backward, right and left. Sometimes 

 the fly came nearer the tumbler and under such circumstances 

 it often remained in its vibratory flight in this new situation. 

 As it approached to within about three feet of the tumbler the 

 excursions shortened and the fly oriented more accurately to the 

 source of the odor, though the flight still showed considerable 

 vibration to right and left while the head of the fly was directed 

 generally toward the tumbler. When about two feet from the 

 tumbler, the vibratory movements grew less and less extensive and 

 the flight became more rapid and more accurately directed toward 

 the tumbler. The last six or eight inches of the journey was made 

 in nearly a straight line to the edge of the tumbler or to its base. 



