THE GRAPE PHYLLOXERA IN CALIFORNIA. 
51 
single lots containing individuals incubating under the same average 
temperatures but belonging to more than one year have been com- 
bined. 
Table IX. 
-Incubation of the eggs of the grope phylloxera on living roots, 
Walnut Creek, Calif., 1013-1915. 
Lot number. 
Number 
of eggs. 
Average 
tempera- 
ture. 
Incuba- 
tion. 
Months or month. 
1 
19 
11 
11 
6 
( 2 ) 
28 
( 2 ) 
3 
11 
23 
26 
21 
11 
45 
23 
8 
o F> 
56.8 
57 
58 
58.5 
60 
61.8 
62 
63 
64 
66 
68 
69 
70.5 
71.5 
72 
72.5 
73 
73.2 
Days. 
119.0 
15.1 
14.8 
15.0 
12.3 
11.2 
9.0 
9.0 
9.7 
3 9.5 
10.5 
3 8.2 
3 7.7 
9.4 
8.4 
3 7.7 
3 7.0 
3 6.4 
March to April. 
2 
April. 
3 
April to May. 
4 
Do. 
5... 
Do. 
6 
May to June. 
7... 
Do. 
8 
Do. 
9 
June. 
10. . . 
Do. 
11 
September to October. 
12 
June to October. 
13 
14 
June to September. 
Do. 
15 
August. 
16 
July to September. 
17 
Do. 
18 
July. 
Maximum, 20 days. 
2 About : 
3 Minimum, 6 days. 
Many of the lots contained a very small number of individuals, 
but in the main the incubation stage became progressively shorter 
as the average temperature rose. Between the temperatures of 56.8° 
and 62° F. the incubation periods are rapidly reduced, while between 
62° and 73.2° the reduction is much less rapid in proportion to the 
rise in temperature. This is a somewhat similar condition to that 
found in the cellar records. 
It is evident that the stage was shortest during the months of July 
and August, and* longest during the months of March and April. 
Records began as early in the year as March 31, and closed as late 
as October 5. Two of the individuals in lot 1 incubated in the maxi- 
mum period of 20 days (Mar. 31 to Apr. 20) under an average tem- 
perature daily of 56.8° F. The minimum of six days was reached 
by IT individuals in each of the months from June to September 
under average daily temperatures of from 66° to 73.2° F. 
The condition of food had no apparent effect upon the duration 
of the egg stage. Eggs deposited by radicicoles which had developed 
from eggs deposited by gallicoles received from Virginia incubated 
in the same average period as those descended from radicicoles of 
many generations, and eggs deposited by nymphicals incubated pre- 
cisely as did those laid by normal radicicoles. Individual incubation 
records, both of eggs reared in the laboratory cellar and of others 
reared on living vines, are given in connection with the development 
of the radicicoles under the same conditions in the section on " De- 
velopment of the radicicole larva," pages 54, 55, 57, 60-62, and 63. 
