2 BULLETIN 345, TJ. S. DEPARTMENT OF AGRICULTURE. 



1914 at New Orleans, La., at which place Mr. T. E. Holloway rendered 

 great assistance. During the summer of 1914 an extended series of 

 experiments was carried out by Mr. A. W. J. Pomeroy. After the 

 severance of his connection with the bureau at the end of October 

 the experiments which he had under way were continued during the 

 fall by Mr. J. L. Webb, and during the winter months the writer 

 continued the work in the greenhouses of the Arlington experiment 

 farm of the Bureau of Plant Industry. 



METHODS USED IN THE PREOVIPOSITION EXPERIMENTS. 



In the experiments to determine the length of the preoviposition 

 period (i. e., the time between the emergence of the adult fly and the 

 first deposition of eggs) laboratory-bred flies were used. The breed- 

 ing was carried out in a systematic way, and several strains or "pure 

 lines" were followed out through five or six generations. Most of 

 the strains were started from a small number of larvae or pupas found 

 in manure piles, and the first flies to emerge from material thus col- 

 lected were used as the parents of the strain. In one case, however 

 a strain was started from a pair of flies taken in coitu on July 25, 

 1914. Eggs were deposited on August 2, and breeding of this strain 

 was continued through six generations. 



The adult flies were kept in small cages. A type of cage found 

 very satisfactory for this work was 22 inches high by 12 inches square. 

 The framework was of soft pine 1 inch square. The top, bottom, 

 and three sides were covered with bronzed screen wire, 16 mesh per 

 inch. The fourth side, or front of the cage, was covered with screen 

 wire about 8 inches down from the top. Below this was a board 

 about 8 inches wide, in which was cut an armhole 5 inches in diame- 

 ter. A sleeve of closely-woven black cloth was tacked over this. 

 Below the board was fitted a drawer 4 inches deep, in which food 

 and material for deposition were kept. Cages of this size were easily 

 and quickly handled, and any part of the interior of the cage could 

 be easily reached through the armhole, the sleeve preventing the 

 escape of any flies during manipulations. The sliding drawer at the 

 bottom of the cage made it possible to remove the contents and exam- 

 ine them for eggs without permitting any flies to escape. These cages 

 were kept on the shelves of a screened insectary and were protected 

 from the direct rays of the sun most of the day, but were freely 

 exposed to air currents and to the outdoor conditions of temperature 

 and humidity. 



Flies were transferred to these cages soon after emergence and 

 supplied with food and media for oviposition. The cages were 

 examined daily; any dead flies were removed and the sex noted at 

 the time of removal. In this way at the end of the experiment the 

 total number of males and females was summed up, and the length 

 of life of each fly in the lot was known. The manure or other medium 



