28 
BULLETIN 427, IT. S. DEPAKTMEKT OF AGMCULTUKE. 
A fairly average record of a pair of adults which mated October 
29, 1914, is as follows: 
October 31. — 40 eggs. 
November 1. — 63 eggs. 
November 2. — 28 eggs. 
November 4. — 41 eggs. 
November 5. — 18 eggs. 
November 8. — 19 eggs. Male dead. 
November 10. — 6 eggs. 
November 12. — 3 eggs. 
November 13. — eggs. Female dead. 
SEASONAL HISTORY. 
NUMBER OF GENERATIONS. 
The number of generations in one year, as might be expected, is 
subject to the wide irregularity shown in the separate stages, and to 
temperature and other natural influences. 
By taking the first to emerge from each brood, six generations are 
theoretically possible. In reality this would include five complete 
generations, and the beginning of the sixth. 
By starting several generations in each month for almost three 
years, it was possible to determine the average length of generations 
for the different months of the year. 
Table 7 gives the results obtained: 
Table 7. — Length of generations of the potato tuber moth. 
Month of starting 
generation. 
January . 
February 
March . .". 
April 
Approxi- 
mate 
length of 
Days. 
90 
Month of starting 
generation. 
May. . . . 
June . . . 
July.... 
August 
Approxi- 
mate 
length of 
genera- 
tion. 
Days. 
50 
40 
30-35 
30-35 
Month of starting 
generation. 
September 
October. .. 
November 
December. 
Approxi- 
mate 
length of 
genera- 
tion- 
Days. 
45 
70-75 
92 
95 
Consecutive generations for a year, using the first to emerge, may 
be plotted as follows: 
1st Gen. 
2nd Gen. 
Plot A. 
3d Gen. 4th Gen. 5th Gen. 
6th Gen. 
Jan. 
Feb. Mar. 
Apr. 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. Nov, 
Dec. 
This shows plainly that even in the more severe years six genera- 
tions may be obtained, using the first to emerge from each brood. 
By using the last to emerge from each brood, the number of genera- 
tions is reduced as the following plot shows. 
