THE GRAPE PHYLLOXERA 1ST 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 phylloxera? 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 



