THE GRAPE PHYLLOXERA IN CALIFORNIA. 37 
period, varying from one to six weeks, ensues, and after this the first 
molt occurs. In the course of from two to six weeks after the first 
molt three additional molts take place, and at the conclusion of the 
fourth molt the phylloxera is mature. This spring growth and de- 
velopment, as observed in the vineyard and in cages, is extended over 
a period of about three and a half months, and usually occurs during 
the period from February 15 to April 15. The commencement of 
growth in phylloxera is noted to be coincident with the first move- 
ment of sap in the vine, and naturally both are influenced by pre- 
vailing meteorological conditions. Upon reaching the adult stage 
the hibernant immediately begins the deposition of its eggs, and in 
this manner the series of parthenogenetic generations destined to 
continue through the season is commenced. 
Measurements. — During the winter of 1913-14 hibernated larvae 
were measured at certain intervals to determine at what time the 
spring growth started. On October 27, 1913, seven individuals 
which had recently hibernated averaged 0.333 mm. in length and 
0.202 mm. in maximum width ; on January 6, 1914, four individuals 
which had hibernated in October, 1913, averaged 0.337 mm. in length 
and 0.198 mm. in maximum width; on February 23, 1914, four indi- 
viduals averaged 0.410 mm. in length and 0.217 mm. in maximum 
width; and on March 10, 1914, five individuals averaged 0.421 mm. 
and 0.241 mm., respectively. Between October and January there 
was no difference in size, but between January 6 and February 23 
there was a marked difference, both individually and collectively, 
showing that between these dates the hibernants had begun to feed. 
The measurements of the individuals taken on March 10 showed 
that considerable growth occurred between February 23 and that 
date. None of the insects measured had molted, and observations 
showed that perceptible growth did not begin before February 10. 
The average length of the beak of the newly hatched radicicole 
destined to hibernate is slightly over 0.2 mm., but after it has been 
inserted in the root it becomes somewhat telescoped and measures 
about 0.17 mm. 
The majority of the hibernants before they start to grow are 
smaller than the newly hatched radicicoles, and therefore they actu- 
ally shrink in size after they hatch from the egg and settle to 
hibernate. Those that feed before hibernating do not shrink to 
such a small size. 
Hibernation in vineyards. — In the vineyards it has been observed 
that the phylloxeras enter into hibernation as early as September 15 
and as late as December 15. Prior to October 1 only a small per- 
centage of hibernants have been found, and after November 20 
