46 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 



adults lived on a healthy Muscat root on tuberosities, their egg- 

 laying period being from August 28 to September 26, under an 

 average temperature of 64° F. One of them did not commence de- 

 positing eggs until the sixth day after it matured, having moved 

 about considerably meanwhile. The fourth-generation phylloxerse 

 wintered on the same root upon which their immediate progenitors 

 had oviposited and matured in the spring of 1914. Of these, 3 

 adults laid 79 eggs in 42 days (aggregated) or 1.9 eggs per diem per 

 adult. The maximum number for. one day for a single adult was 

 4 and the longest egg-laying period 24 days. In this period one 

 adult laid 56 eggs. The egg-laying period, toward the end of which 

 the root became lightly decayed, ran from April 6 to May 8, under 

 a temperature averaging 58° F. 



In the ensuing generations throughout 1914 and 1915, the egg- 

 laying records were mostly incomplete. Records of the fifth gen- 

 eration on Muscat in the period May 28 to June 11 show an average 

 number of eggs per diem per adult to be 2.8, the largest number 

 deposited in a single day by a single adult being 5. The average 

 temperature was 65° F. Records of the seventh generation on a 

 slightly decayed Grenache root, July 29 to August 8, show an av- 

 erage number of eggs per diem per adult to be 5.4, and the maximum 

 number of eggs laid in a single day to be 7. The temperature aver- 

 aged 71° F. The records of these two lots are much too meager for 

 comparisons. 



In comparing the egg production on the living vines with that on 

 root cuttings, it should be stated that during the summer and fall 

 months the aphids on the former enjoyed higher temperatures. This 

 advantage was somewhat counterbalanced by the greater daily 

 fluctuations in temperature which took place on caged living vines 

 and which frequently resulted in a daily minimum lower than that 

 simultaneously occurring in the laboratory cellar in which the root 

 cuttings were kept. 



As a general rule the egg-depositing capacity of the adult in- 

 creases rapidly after maturity, and after the zenith is reached de- 

 creases slowly, so that half the complement of eggs is deposited 

 before one-third of the egg-laying period is completed. 



The condition of the food is the chief factor in the production of 

 eggs, but there is also a meteorological control. Frequent fluctuations 

 in temperature and humidity adversely affect deposition. 



Extrusion of the egg. — During the process of egg extrusion, which 

 occupies from 20 to 40 minutes, the abdomen of the adult radicicole is 

 considerably distended. It is apparent, therefore, that when an 

 adult deposits 23 eggs within one day, extrusion will be taking place 

 intermittently for a very considerable part of the day. During the 



