THE GRAPE PHYLLOXERA IN CALIFORNIA. 



69 



from equally succulent pieces of severed roots. They show a con- 

 siderable variation in dimensions, but, being hibernants, their aver- 

 age dimensions are less than those of the summer generations under 

 equally favorable food-supply conditions; for among the hibernant 

 adults there always may be found a considerable number of small- 

 sized individuals which evidently owe their physical inferiority to 

 the vicissitudes of the long hibernation period. Radicicoles raised on 

 fleshy and succulent nodosities attain an average size of about 1 by 

 0.55 mm., those raised during the summer on other parts of the root 

 system average slightly less, and the hibernant individuals average 

 0.75 by 0.50 mm. 



Radicicole molts.— -The radicicole, in common with other forms of 

 the phylloxera, invariably molts four times. 



In 1914 and 1915 records of molts were taken, and Tables XX and 

 XXI indicate molting records of 20 individuals reared on severed 

 roots in the laboratory cellar during the summer of 1914. 



Table XX. — Molting records of 20 radicicoles of the grape phylloxera, summer 

 of 191J h Walnut Creek, Calif. 



Indi- 

 vidual 

 No. 



Date egg 

 batched. 



Date of 

 first 

 molt. 



First 

 instar. 



Date of 

 second 

 molt. 



Second 

 instar. 



Date of 

 third 

 molt. 



Third 

 instar. 



Date of 

 fourth 

 molt. 



Fourth 

 instar. 



Total 

 grow- 

 ing 

 period. 



Aver- 

 age 

 tem- 

 pera- 

 ture. 



1 

 2 



3 



4 



July 22 



...do.. . 



July 23 



.do. . . 



Aug. 6 

 Aug. 7 

 Aug. 6 

 ...do 



Days. 

 15 

 16 

 14 

 14 

 14 

 10 

 10 

 11 

 11 

 11 

 12 

 12 

 11 

 13 

 14 

 14 

 15 

 17 

 19 



Aug. 9 



...do 



...do.... 



Days. 

 3 

 2 

 3 



Aug. 11 

 ...do.... 

 Aug. 13 



Days. 

 2 

 2 

 4 



Aug. 14 



...do 



Aug. 16 



Days. 

 3 

 3 

 3 



Days. 

 23 

 23 

 24 



°F. 



68 

 68 

 68 



5 

 6 

 7 

 8 

 9 

 10 

 11 

 12 

 13 

 14 



July 24 

 July 25 



...do.... 



...do.... 



...do.... 



...do 



...do.... 



...do.... 



...do.... 



...do.... 



...do 



...do.... 



...do.... 



...do.... 



...do.... 



...do 



Aug. 7 

 Aug. 4 



...do.... 

 Aug. 5 



...do.... 



...do.... 

 Aug. 6 



...do.... 

 Aug. 5 

 Aug. 7 

 Aug. 8 



...do.... 

 Aug. 9 

 Aug. 11 

 Aug. 13 



Aug. 9 

 Aug. 6 



...do 



Aug. 8 



...do.... 

 Aug. 9 

 Aug. 8 



...do.... 



...do 



Aug. 10 



...do.... 



...do.... 

 Aug. 13 

 Aug. 14 

 Aug. 20 



2 



2 

 2 

 3 

 3 

 4 

 2 

 2 

 3 

 3 

 2 

 2 

 4 

 3 

 7 



Aug. 11 

 Aug. 8 



...do 



Aug. 9 

 Aug. 11 

 Aug. 12 

 Aug. 11 



...do 



Aug. 9 



2 



2 

 2 

 1 



3 

 3 

 3 

 3 

 1 



Aug. 14 

 Aug. 9 

 Aug. 11 



...do 



Aug. 13 

 Aug. 14 

 Aug. 13 

 Aug. 14 

 Aug. 11 



3 

 1 



3 

 2 

 2 

 2 

 2 

 3 

 2 



21 

 15 



17 

 17 

 19 

 20 

 19 

 20 

 17 



68 

 68 

 68 

 68 

 68 

 68 

 68 

 68 

 68 



15 

 16 

 17 



18 



19 



120 



Aug. 13 

 Aug. 12 

 Aug. 15 

 Aug. 17 

 Aug. 24 



3 

 2 

 2 

 3 

 4 



Aug. 15 

 ...do 



Aug. 18 

 ...do.:.. 



Aug. 28 



2 

 3 

 3 

 1 



4 



21 

 21 



24 

 24 

 34 



68 

 68 



68 

 68 

 68 



























1 Hibernant died unmolted Oct . 11. 

 Table XXI. — Summary of Table XX. 



Average 

 period. 



Maxi- 

 mum 

 period. 



Mini- 

 mum 

 period. 



First instar, 19 individuals 



Second instar, 18 individuals 



Third instar, 17 individuals 



Fourth instar, 17 individuals 



Developmental period, 17 individuals 



Days. 

 13.3 

 2.9 

 2.5 

 2.5 



Days. 

 19 



7 

 4 

 4 



21. 2 



34 



Days. 



