32 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 
confusion, it is assumed that there are five generations annually, 
since this number is about the average in a vineyard in which the 
sap moves early, although there might be, under certain conditions, 
from one to eight or even nine generations within a single year. 
The hibernant generation having matured in April, the succeeding 
generation matures about the time the canes have ended their first 
rapid growth, approximately the end of May. Succeeding genera- 
tions mature on about the following average dates : Second, July 6 ; 
third, August 15 ; fourth, September 30 ; the fifth generation hiber- 
nating. 
A variable percentage of the larvae of generations 2, 3, and 4 
becomes nymphs, and these later emerge from the ground as winged 
insects and either fly away or are borne off on the wind. Large 
numbers of these are caught in spider webs. Many of the newly 
hatched larvae develop a wandering tendency just after they have 
issued from the eggshell and seek to emigrate to other vines either 
through the soil or over the surface of the ground. Large numbers 
of these migrating larvae are also caught in spider webs on the surface, 
and while only a small percentage reach their destination, a single 
individual may start a new infestation. Those of the larvae that suc- 
ceed in fastening upon a root or rootlet develop as radicicoles. 
The winged forms normally occur from June to October, and the 
wandering larvae are found from July to September. 
During July and August, when the adult radicicoles are most 
prolific, incubation and development proceed most rapidly, and the 
phylloxera may be said then to have reached its most active stage. 
It is at this stage that the greatest damage is done to the roots of the 
vines, although the effects are not generally apparent until the fall 
and winter following, when the lesions formed during the summer 
have decayed. 
At the end of September a few of the newly hatched larvae 
hibernate, and throughout October successive generations become 
hibernants, so that by the end of the month a large majority of the 
phylloxera have reached this stage. During November and the 
first half of December, a few mature radicicoles and growing larvae 
may be found, but after the middle of December, it is unusual to 
find any form but the hibernating larva. 
Under conditions of abundant food supply, the period of egg 
deposition of the radicicoles averages 45 days and may reach a 
maximum of 110 days. This average is nearly constant throughout 
the season. The average number of eggs deposited is about 117, 
but under certain conditions the number may be increased to 486. 
The daily average number is about 2J+ e ggs, and as many as 23 
eggs have been deposited in 24 hours by a single phylloxera. 
