30 
BULLETIN" 427, U. S. DEPARTMENT OF AGRICULTURE. 
In examining this table it mnst be borne in mind that the results 
given are for a particular year, and great variations are possible from 
similar months in other years. One example will be sufficient to 
illustrate this point: During the middle of April, 1914, the mean 
temperature averaged about 66°, and during this time eggs of the 
tuber moth were hatching in from 8 to 9 days. During the same 
period of 1915, with the average mean temperature about 59° F., the 
egg stage lasted from 12 to 14 days. All stages of the insect vary 
so greatly that it is difficult to foretell how long a generation will 
take. 
OVERLAPPING OP GENERATIONS. 
From the foregoing examples it is evident that all stages of the 
tuber moth exist throughout the year in Southern California, and 
consequently the broods can not be distinguished. Many writers have 
estimated the numbers of broods or generations by the abundance of 
moths at different times of the year. If conditions are considered, 
it may be seen that food and temperature govern this condition. In 
summer, with an abundant food supply, the insect multiplies with 
great rapidity, adults become abundant, and the impression of the- 
emergence of a brood is given. If plots A (p. 28) and B (p. 29) are 
compared, the overlapping of generations may be understood. 
By placing one over the other as in plot C, the shaded areas 
show the time adults are emerging. The broken lines are from 
plot B. 
Plot C. 
1st Gen. 
2nd Gen. 
3rd Gen. 
4th Gen. 
5th Gen. 
1st Gen. 
2nd Gen. j 3rd Gen. 4thJGen. 5th G|en. 
6th Gen. 
WA 
I 
■ 
'wmk 
Jan. 
Feb. Mar. A] 
1 1 
Dr. May. Jur 
ie. July. Au 
g. Sept. 
Oct. 
Nov. 
Dec. 
This diagram indicates that although the generations may secure 
an even start at the beginning of the year, by late summer and fall 
the first to emerge from the fifth generation are appearing at a time 
when there are still adults from the fourth generation emerging. This 
explains the presence of all stages of the insect at all times of the year, 
and indicates that from the economic side a knowledge of the life his- 
tory of the moth is of little importance, except as it shows the possi- 
bilities of reproduction. 
HIBERNATION. 
During the discussion of the effect of temperature on the various 
stages of the tuber moth the impression was given that there is no 
hibernation for any length of time in southern California. This is 
surely the case under normal conditions, though possibly there is no 
