284 



Chemotropic Responses of Insects 



(5) Glacial acetic acid. Gla«ial acetic acid was not observed to 

 exercise any marked chemotropic attraction as the following experiments 

 indicate. 



Aug. 27-29. 50 c.c. water 6 



21-23. „ „ 1 c.c. 



21-22. 



24-27. 

 27-29. 

 24-27. 



•5 c.c. 

 •5 c.c. 

 •5 c.c. 

 •1 c.c. 



(6) Ethyl alcohol and glacial acetic acid. Unlike either of these 

 substances, when used separately, a mixture of the two was found to be 

 markedly attractive. Ethyl alcohol and acetic acid when brought into 

 contact form small quantities of ethyl acetate and, as shown in Barrow's 

 experiments (1907), ethyl acetate exercises a marked attraction for 

 Drosophila ampelophila. The amount of ethyl acetate formed by using 

 such small quantities of the two substances as 1 per cent, of ethyl 

 alcohol and 0-05 c.c. of acetic acid under outdoor conditions must be 

 very small. In each experiment 50 c.c. of ethyl alcohol or water was used. 



Exp. 1. Aug. 19-21. 



21-23. 



21-22. 



22-23. 



10% ethyl alcohol + 1 

 10% „ - 



10% „ +1 



water + 1 



10% ethyl alcohol + ■ 



water + • 



10% ethyl alcohol + 

 10% „ - 



c.c. glacial acetic acid 



c.c. 

 c.c. 

 c.c. 

 c.c. 



5. 



7. 



8. 



9. 

 10. 

 U. 

 12. 

 12a. 



1.3. 



1.5. 



I5a. 



14. 



14o. 



27-29. 



22-23. 



23-24. 



24-27. 



5% 

 5% 



5% 

 5% 



5% 



5% 



5% 



2-5% 



2-5% 



2-5% 



2-5% 



1% 

 1% 

 1% 

 1% 



+ -5 c.c. 



+ -5 c.c. 



water 



