614 



SCIENCE 



[N. S. Vol. XLHI. No. 1113 



traps, 9| inches high, and 6 inches in diameter 

 at the base : Ammonium carbonate U. S. P. 

 (contained about 97 per cent, of ammonium 

 acid carbonate and ammonium carbamate), 

 ammonium sulphide solution, ammonium hy- 

 droxide, ethyl alcoholic solutions of skatol and 

 indol, ethyl alcohol, acetic, formic, butyric 

 and valerianic acids, hydrogen sulphide solu- 

 tion and carbon dioxide. The traps which 

 volatilized carbon dioxide were equipped with 

 Erlenmeyer flask droppers, which delivered 

 dilute hydrochloric acid a drop at a time on to 

 bits of limestone in the pan of the trap. By 

 this method a small but fairly constant amount 

 of carbon dioxide was evolved throughout a 

 number of hours. A trap was similarly 

 equipped for use in the ammonium hydroxide 

 experiment. 



The experiments were performed at a place 

 where flies were always present, but never ex- 

 cessively abundant. 



Negative results were obtained in all but 

 the ammoniucm hydroxide and ammonium car- 

 bonate experiments. The results of ten am- 

 monium carbonate trap experiments are 

 summarized below. 



House flies were attracted to the traps 

 which contained ammonium carbonate. Small 

 amounts of water and carbon dioxide, both 

 constituents of ammonium carbonate, were not 

 sought by flies, and it is concluded that the 

 other constituent, ammonia, was the attracting 

 agent. 



The best results were obtained when water 

 was added to the ammonium carbonate, be- 

 cause it prevented the deposit of a powdery 



layer of the less volatile ammonium acid car- 

 bonate which otherwise hindered the escape of 

 ammonia. 



The single ammonium hydroxide trap caught 

 three female house flies during twenty-five 

 hours' exposure. 



Since the flies caught in the ammonium 

 carbonate traps were largely females (90.7 per 

 cent.), it was desired to know whether am- 

 monia was particularly attractive to females, 

 or whether females were unusually abundant in 

 the vicinity of the experiments. Under ordi- 

 nary conditions remote from breeding places 

 the proportion of sexes in the house fly is about 

 equal, with a slight excess of females.* 



Accordingly, traps baited with food materials 

 (milk, sweet soda water), were maintained in 

 the vicinity of the ammonium carbonate ex- 

 periments from July 21 to July 29. During 

 this time 274 house flies were captured, 45.9 

 per cent, of which were males, and 54.0 per 

 cent, females. In the same period, the am- 

 monium carbonate traps caught 65 flies, 7.6 

 per cent, males and 89.2 per cent, females. 

 Ammonia attracted a great preponderance of 

 females. 



Oviposition Experiments 

 Acidulated horse manure, timothy chaff, pine 

 sawdust, and cotton were treated in such a way 

 that they evolved ammonia. They were then 

 exposed in a place frequented by flies, and after 

 a period which varied from 3 to 99 hours in 

 the individual experiments, counts were made 

 of the egg-masses which had been deposited. 

 Two or more eggs, placed together, were con- 

 sidered an egg-mass, but the large majority of 

 clusters contained many more than two eggs. 

 Occasional single eggs were ignored. 



Oviposition in Acidulated Horse Manure. — 

 The purpose of this series of experiments was 

 to show whether fresh horse manure which did 

 not volatilize ammonia would still induce the 

 house fly to oviposit, and whether such manure, 

 when again volatilizing ammonia, would at- 

 tract the female fly. Fresh horse manure was 

 treated with dilute hydrochloric acid so that 



* Hewitt, ' ' The House Fly {Musca domestiea 

 L.)," etc., Cambridge, England, 1914, p. 98. 



