286 Chemotropic Responses of Insects 



On Aug. 24-29 (Exp, 17) two vessels were placed closely together 

 in the same trap: one contained 50 c.c. of 5 per cent, ethyl alcohol, and 

 the other 50 c.c. of 1 per cent, glacial acetic acid. The vapours of the two 

 solutions coming in contact would produce very minute quantities of 

 ethyl acetate. This, however, proved to possess powerful attractive 

 properties, 365 Diptera pertaining to various species being entrapped. 

 In another experiment (No. 16) (Aug. 24-27), 50 c.c. 2 per cent, glacial 

 acetic acid was used, and the same quantity of 10 per cent, ethyl alcohol 

 was placed in a second vessel as before, and 204 Diptera were attracted 

 during 42 hours exposure. The question arises whether it is the vapour 

 of the ethyl acetate that is alone responsible for this attraction, or the 

 mixed vapours of the ethyl alcohol, acetic acid and ethyl acetate that 

 produced the effect. This problem is at present unanswered. As a control 

 on the same days (Aug. 27-29) 5 per cent, ethyl alcohol attracted only 

 eight Diptera. 



An analysis of the species attracted and the number of each sex 

 obtained is given on p. 285. The numbers at the head of each column 

 refer to those allotted to each of the foregoing experiments. The figures 

 opposite each species refer to the number of individuals attracted, the 

 upper figures representing males and the lower figures females : figures 

 bearing * are cases in which the sexes of the individuals were not 

 determined. 



7. Ethyl acetate. We have so far only conducted a few experiments 

 with this ester. From Aug. 2-8 an emulsion of 10 c.c. of ethyl acetate in 

 50 c.c. of water attracted only 39 Diptera. From Aug. 8-12 a mixture 

 of 5 c.c. ethyl acetate and 50 c.c. of a 25 per cent, solution of cane molasses 

 proved attractive. During the same period a trap containing 25 c.c. 

 of beer in place of the ethyl acetate attracted 108 examples of various 

 Diptera. 



8. Methyl acetate. 



Aug. 12-14. 5 c.c. water + 10 c.c. methyl acetate, 3 Diptera, 

 „ 15-16. 5 c.c. 10% ethyl alcohol + a few drops of methyl -acetate. 11 Diptera. 



9. Amylic acetate. On Aug. 16-19 an emulsion consisting of 33 per 

 cent, amylic acetate in water attracted seven Diptera : with 20 per cent, 

 amylic acetate six Diptera were attracted, and with 9 per cent, acetate 

 10 Diptera responded. 



(10) Butyric and valerianic acids. Normal butyric acid in water 

 exhibited no attractive properties, but traces of this substance in ethyl 

 alcohol proved very attractive, this property probably being due to the 

 ethyl butyrate formed, Iso-butyric acid gave less satisfactory results. 



