THE GRAPE PHYLLOXERA IN CALIFORNIA. 
71 
age of 61.75° F. this period was 24.75 days, under 65° F. it was 
almost 22 days, and under 68° F. it was lowered to 20.3 days 
(individual on unthrifty root disregarded). Under the lower tem- 
peratures all the instars are correspondingly longer than under the 
highest midsummer temperature, but the first instar is proportion- 
ately less lengthened' than are those following it, a phenomenon 
that becomes quite apparent in the case of the hibernants, provided 
their first instar be considered in a restricted sense to cover only that 
period between the time when they commence feeding in spring and 
the date of the first molt. The hibernant feeds for two and one-half 
weeks before and for three weeks after its first molt, while in mid- 
summer the larva feeds for 13 days before and for 8 days after its 
first molt before it matures. 
MAXIMUM AND MINIMUM GENERATIONS YEARLY. 
In 1911 overwintered adult radicicoles matured at the end of 
April, throughout May and June, and as late as July 7. Eggs of 
the first generation were deposited from the end of April until 
October 1. From the earliest eggs there followed seven complete 
generations from hibernant to hibernant inside of the one year. No 
observations were taken of the hatching of the late eggs deposited 
by late first-generation phylloxera? in September, but in the light of 
contemporary observations on individuals of later generations there 
is no doubt that a certain percentage of these late eggs would have 
hatched into hibernants, thus giving a minimum of one generation 
per annum. In 1915, taking advantage of a hibernant which ma- 
tured exceptionally early in the spring, it was possible to secure 
eight complete generations within the year. Table XXIII records 
the development of these generations. 
Table XXIII. — Maximum series of generations of radicicoles of the grape 
phylloxera, reared under cellar conditions, Walnut Creek, Calif., 1915. 
Generation No. 
Date of egg 
deposition. 
Date of egg 
hatching. 
Date insect 
matured. 
Genera- 
tion 
cycle. 
Temper- 
ature 
(average). 
li 
—1914 
Feb. 26,1915 
Apr. 27,1915 
June 7,1915 
July 5, 1915 
July 28,1915 
Aug. 23,1915 
Sept. 25, 1915 
Oct. 27,1915 
—1914 
Mar. 19,1915 
May 11,1915 
June 16,1915 
July 14,1915 
Aug. 4, 1915 
Aug. 31,1915 
Oct. 7, 1915 
Nov. 10,1915 
Feb. 26,1915 
Apr. 22,1915 
June 5, 1915 
July 4, 1915 
July 28,1915 
Aug. 23,1915 
Sept. 23, 1915 
Oct. 27,1915 
—,1916 
Days. 
°F. 
2 
55 
39 
27 
23 
26 
31 
32 
58.25 
3 
61.20 
4 
64 50 
5 
69.50 
6 
68.50 
7 
67.00 
8 
62.50 
9 1 
Hibernant. 
In this experiment the food supplied to the phylloxeras was, as 
far as one could judge, of equal quality and very nourishing. The 
influence of temperature is noticeable. 
