THE GRAPE PHYLLOXERA IN CALIFORNIA. 
69 
from equally succulent pieces of severed roots. They show a con- 
siderable variation in dimensions, but, being hibernants, their aver- 
age dimensions are less than those of the summer generations under 
equally favorable food-supply conditions; for among the hibernant 
adults there always may be found a considerable number of small- 
sized individuals which evidently owe their physical inferiority to 
the vicissitudes of the long hibernation period. Radicicoles raised on 
fleshy and succulent nodosities attain an average size of about 1 by 
0.55 mm., those raised during the summer on other parts of the root 
system average slightly less, and the hibernant individuals average 
0.75 by 0.50 mm. 
Radicicole molts. — The radicicole, in common with other forms of 
the phylloxera, invariably molts four times. 
In 1914 and 1915 records of molts were taken, and Tables XX and 
XXI indicate molting records of 20 individuals reared on severed 
roots in the laboratory cellar during the summer of 1914. 
Table XX. — Molting records of 20 radicicoles of the grape phylloxera, summer 
of 1914, Walnut Creek, Calif. 
Indi- 
vidual 
No. 
Date egg 
batched. 
Date of 
first 
molt. 
First 
instar. 
Date of 
second 
molt. 
Second 
instar. 
Date of 
third 
molt. 
Third 
instar. 
Date of 
fourth 
molt. 
Fourth 
instar. 
Total 
grow- 
ing 
period. 
Aver- 
age 
tem- 
pera- 
ture. 
1 
2 
3 
4 
July 22 
...do.. . 
July 23 
.do. . 
Aug. 6 
Aug. 7 
Aug. 6 
...do 
Days. 
15 
16 
14 
14 
14 
10 
10 
11 
11 
11 
12 
12 
11 
13 
14 
14 
15 
17 
19 
Aug. 9 
...do 
...do.... 
Days. 
3 
2 
3 
Aug. 11 
...do 
Aug. 13 
Days. 
2 
2 
4 
Aug. 14 
...do 
Aug. 16 
Days. 
3 
3 
3 
Days. 
23 
23 
24 
°F. 
68 
68 
68 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
July 24 
July 25 
...do 
...do.... 
...do.... 
...do 
...do.... 
...do.... 
...do.... 
...do.... 
...do.... 
...do.... 
...do.... 
...do.... 
...do.... 
...do 
Aug. 7 
Aug. 4 
...do 
Aug. 5 
...do 
...do.... 
Aug. 6 
...do 
Aug. 5 
Aug. 7 
Aug. 8 
...do 
Aug. 9 
Aug. 11 
Aug. 13 
Aug. 9 
Aug. 6 
...do 
Aug. 8 
...do 
Aug. 9 
Aug. 8 
...do 
...do.... 
Aug. 10 
...do 
...do.... 
Aug. 13 
Aug. 14 
Aug. 20 
2 
2 
2 
3 
3 
4 
2 
2 
3 
3 
2 
2 
4 
3 
7 
Aug. 11 
Aug. 8 
...do 
Aug. 9 
Aug. 11 
Aug. 12 
Aug. 11 
...do 
Aug. 9 
2 
2 
2 
1 
3 
3 
3 
3 
Aug. 14 
Aug. 9 
Aug. 11 
...do 
Aug. 13 
Aug. 14 
Aug. 13 
Aug. 14 
Aug. 11 
3 
1 
3 
2 
2 
2 
2 
3 
2 
21 
15 
17 
17 
19 
20 
19 
20 
17 
68 
68 
68 
68 
68 
68 
68 
68 
68 
15 
16 
17 
18 
19 
120 
Aug. 13 
Aug. 12 
Aug. 15 
Aug. 17 
Aug. 24 
3 
2 
2 
3 
4 
Aug. 15 
...do 
Aug. 18 
...do 
Aug. 28 
2 
3 
3 
1 
4 
21 
21 
24 
24 
34 
68 
68 
68 
68 
68 
1 Hibernant died unmolted Oct . 11. 
Table XXI. — Summary of Table XX. 
Average 
period. 
Maxi- 
mum 
period. 
Mini- 
mum 
period. 
Days. 
13.3 
2.9 
2.5 
2.5 
Days. 
19 
7 
4 
4 
Days. 
10 
2 
1 
1 
Developmental period, 1 7 individuals 
21.2 
34 
15 
