20 



BULLETIN 1453, IT. S. DEPARTMENT OF AGRICULTURE 



oviposition to the laying of the last eggs, a few days are often inter- 

 spersed on which no eggs are laid. The oviposition period varies in 

 length with the temperature, as does the postoviposition interval, but 

 in cool weather the latter is proportionately longer than the oviposi- 

 tion period. 



LONGEVITY OF ADULTS 



The length of life of mated and fed adults was from 1 to 39 days, 

 as shown in Tables 2 and 4. None of the unfed flies kept in a 

 refrigerator at 48 to 50° F. lived as long as 30 days, the longest life 

 of a fed fly in the refrigerator. The data in Table 2 show that the 

 males usually live longer than the females. 



Unmated adults kept without food or water lived as shown in 

 Table 8. Until June 10 the weather was cool or warm, but on 

 June 11 the daily average temperature passed above 80° F. and 

 thereafter remained high. For this reason two divisions of the 

 longevity records are made. The temperatures experienced by the 

 flies included in Table 8 are given in Table 3. 



Table 8. — Longevity of unmated adults of Piophila easel confined without food 

 or water at Washington, D. C, in 1921 



Died on- 



First day... 

 Second day 

 Third day.. 

 Fourth day 

 Fifth day. . 



Flies 



Flies 



emerged i emerged 



May 19 to 



June 11 to 



June 10 



June 22 ! 



3 



5 



4 



95 



103 



150 1 



222 



65 



163 



8 



Died on — 



Sixth day... 

 Seventh day 

 Eighth day. 



Total. 



Flies 



emerged 



May 19 to 



June 10 



30 



Flies 



emerged 



June 11 to 



June 22 



323 



The average longevity of the flies in the first group (Table 8) 

 was 4.3 days and in the later group slightly less than 3 days. The 

 average of the daily mean temperatures experienced by the flies of 

 the first group was 74° F. and by those of the second group 81° F., 

 the difference of. 7° in the averages. of the daily means being appar- 

 ently responsible for the difference of over 1 day in the average lives 

 of the insects. Temperature was the only apparent important 

 variable. 



The females used in the experiment lived longer than the males; 

 the average female life was 4 days and the average male life 3.5 days. 

 When pairs are mated and fed, oviposition usually results and the 

 longevity relation of the two sexes is reversed. A summary of the 

 longevity records of 46 such pairs (Table 2) shows that the males 

 lived an average of 8.5 days and the females 5.1 days. 



SEX RATIOS 



Previous to the work included in this bulletin, the only records of 

 the relative abundance of the sexes were published by Bachmann (£), 

 who believed the males to be in the minority, and by Sakharov (67), 

 who found that of 1.077 flies, 625 were females and 452 were males. 

 The writer has observed little difference in the numbers of the 

 sexes, but has always found a small plurality of males. Of the 864 



