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



Many attempts were made by Mr. Pomeroy to keep isolated pairs 

 of flies under as natural conditions as possible in order to obtain not 

 only the preoviposition period but also the number of depositions per 

 fly and the number of eggs per deposition. The usual method was 

 to remove from a lot of laboratory bred flies the first pair which were 

 found in copulation. After transfer to a separate cage they were 

 supplied with food and a medium for oviposition and were kept under 

 observation in much the same way as the larger lots. The results of 

 the tests with isolated pairs are summarized in Table II. 



The fact that only 7 out of some 30 tests gave any positive results 

 points to the difficulties in obtaining significant data from experi- 

 ments performed under artificial conditions. 



The shortest preoviposition period was about two and one-half days 

 (Table I, lot No. 1). Mr. Pomeroy's original notes on this lot show 

 that the "flies emerged some time between August 18, 10.30 a. m., 

 and August 19, 9.30 a. m.," at which time they were "transferred to 

 cage and supplied with banana, water, and fresh manure. Examined 

 August 20 at 3.30 p. m. No eggs were found. Fresh manure sup- 

 plied. August 21, at 1 p. m., two clusters of eggs were found, 80 to 

 90 eggs in each cluster." Now, if the flies which deposited these eggs 

 had emerged on the afternoon of the 18th the preoviposition period 

 was a little longer than two and one-half days. If they had emerged 

 during the morning of the 19th before 9.30 a. m. the period was a little 

 less than two and one-half days. Other remarkably short periods 

 are to be found in the three 3-day periods shown in the table, and in 

 the four 4-day records. It is reasonable to suppose that if these short 

 periods were found under artificial experimental conditions they 

 would be not at all uncommon under natural conditions. 

 i The longest period was one of 23 days (Table I, lot No. 69). In 

 general it may be said that the shortest records occurred in mid- 

 summer and that the longer ones were obtained during the autumn 

 months. It is true that some long periods were found in summer, 

 e. g., a 14-day and a 16-day record in July, but no short records were 

 ever found during the autumn months. In other words, the length of 

 the preoviposition period is greatly influenced by the temperature. 

 A study of Table I will show that the arrangement according to the 

 increasing length of the period corresponds in a rough way with the 

 order of the decreasing mean temperatures of those periods. The 

 relation between the temperature and the length of the preoviposition 

 period is made clearer in the correlation table (Table III), in which 

 the columns give the preoviposition period in days and the rows 

 represent 2° intervals of temperature. 



