72 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 
In observations with phylloxerae developing on living vines there 
were secured in a period of three years 13 generations, an average of a 
little over four generations a year, but had the earliest eggs of each 
generation been successfully utilized, and had it been possible to 
start the first of the three seasons with the earliest eggs procurable 
in the vineyards, there is no doubt that six, and possibly seven, gen- 
erations could have been developed each year. 
Considering that the hibernant generation occupies a period of 
half a year, it is apparent that if seven generations are to be pro- 
duced in a year, the other six must be passed in an average maximum 
of one month apiece. In summer phylloxerae have been reared from 
egg deposition to maturity in 21 days, but in April, May, and Oc- 
tober the cycle rarely falls below 35 days, so that in the six-month 
period, April 15 to October 15, the average maximum cycle is roughly 
30 days. Thus, in the vineyard, even on vines that move early in 
spring, it is probable that more than seven generations rarely take 
place in 12 months. The period, October 15 to April 15, best rep- 
resents the cycle of the wintering generation, although these dates 
are somewhat arbitrary. 
Under vineyard conditions it is always possible to find hibernant 
phylloxerae as late as the beginning of June. It is also possible 
to find insects going into hibernation as early as September 20. Since 
the mature radicicoles deposit eggs for periods exceeding three 
months, it can be seen readily that the latest eggs of a radicicole 
hibernant maturing in June may develop larvae which proceed to 
hibernate. A minimum of one generation a year thus may occur. 
Observations indicate that this minimum of one generation is not 
common, even on moribund vines with innutritious roots. 
WANDERING RADICICOLE LARVAE OR " WANDERERS." 
By the term " wanderers " are designated those forms (almost all 
newly hatched larvae) which forsake the root on which they issued 
from the egg and seek to reach the surface of the soil or to pass 
through the soil itself, with the object of finding new food. Those 
that strive to reach the surface exhibit in their efforts a very marked 
positive phototropism. It would appear that their first movement 
is simply one of ascending the root and that as soon as they are 
brought into the focus of a ray of light they immediately make it 
their goal, and thus finally ascend to the surface. The initial wan- 
dering movement comes irrespective of light rays, but as soon as 
these rays are brought to bear the activity is very pronounced. The 
conclusion is that the production of individuals destined to wander 
is due to a combination of influences more than to any single influ- 
ence — the crowded condition of the phylloxeras in summer, the decay- 
ing of the roots, especially the fleshy surface rootlets, found on 
