44 



BULLETIN 903, V. S. DEPARTMENT OF AGFJCULTTTRE. 



these pots was about the same as that occurring 2 feet below the soil 

 surface. In the spring of 1915, on the Champion, Lenoir, Catawba, 

 and Isabella, the phylloxera began to grow about March 1. On the 

 first three the bulk of the hibernants were mature April 6, but on 

 the Isabella, which was moribund, more than half were unmolted. 

 This vine was not retained further, but, considering the condition 

 of its roots, it is not probable that any of the phylloxera? would 

 have matured. The vine was too weak to send out new rootlets, and 

 the roots showed much decay. The abundance of phylloxeras the 

 summer previous had doubtless caused this weakness. 



THE RADICICOLE. 



EGG DEPOSITION. 



The adult radicicole commences to deposit eggs within 48 hours 

 after the final molt. Occasionally there occur abnormal individuals 

 which delay deposition of eggs as much as two weeks, and again 

 there are others which fail to deposit eggs but continue alive for 

 some weeks. 



Egg deposition on severed roots.- — Table ITT gives the summarized 

 record of the egg deposition of radicicoles under cellar conditions 

 during the years 1911-12. 



Table TIL — Summarised record of egg deposition of radicicole& of the grape 

 phylloxera under cellar conditions during 1911-12, Walnut Creek, Calif. 



Gener- 

 ation. 



i 

 1 

 2 

 3 

 4 

 3 5-10 



Num- 

 ber of 

 adults. 



52 



45 

 57 

 17 



2 11 



27 



-laying period for gener- 

 ation. 



Apr. 21 to Oct. 1 



May 27 to Sept. 23 



June 29 to Nov. 6 



Aug. 4 to Dec. 7 



Sept. 5 to May 15, 1912. 

 Apr. 26 to Oct. 6 



Number of eggs per 



Days 



in period of 





adult. 





deposition. 



Maxi- 



Mini- 



Aver- 



Maxi- 



Mini- 



Aver- 



mum. 



mum. 



age. 



mum. 



mum. 



age. 



347 



4 



84.6 



110 



2 



55. 3 



486 



10 



192.0 



96 



5 



46.3 



287 



2 



102. 



106 



1 



48.5 



266 



3 



141.8 



96 



2 



44 



119 



31 



67.2 



& 



23 



41.7 



137 



4 



35.5 



47 



3 



21.5 



Aver- 

 age 

 num- 

 ber of 

 eggs 

 per 

 adult 

 per 

 day. 



1.53 



4.1 



2.1 



3.2 



1.6 



1.7 



1 Overwintered generation. 2 Including 3 individuals which matured in 1912. 3 Throughout 1912. 



Neglecting the series of generations 5 to 10, the individuals of which 

 suffered through abnormal food and other conditions, it is shown in 

 Table III that the aphids of the second generation were the most 

 prolific. One aphid deposited 486 eggs in 79 days, an average of 6.3 

 per diem. The greatest number of eggs laid within 24 hours by a 

 single adult was 23 and the longest laying period covered 110 days. A 

 true seasonal average of the number of eggs deposited by each aphid 

 was 117 for 1911 and a similar average of the number of eggs per 

 diem per aphid about 2|. 



