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



In the cellar and incubator during 1913 the phylloxerse developed, 

 on the average, more slowly than in the cellar during 1911 and 1912, 

 notwithstanding higher temperatures in 1913. This resulted from the 

 fact that the food supply was much more succulent in 1911 and 1912. 

 Likewise the phylloxerse developed much more rapidly in the cages 

 in 1913-1915 than in the cellar and incubator combined in 1913, 

 when the temperatures differed slightly (the difference in favor of 

 the cages being about 1° daily). This also was due to the superior 

 food of the living vines. In comparing the phylloxera development 

 in the cellar in 1911-12 with that in the cages in 1913-1915, it would 

 appear that both temperature and food influenced the more rapid 

 development observed in the cages. For 1911 alone the average grow- 

 ing period was 29.37 days. This growth took place on succulent roots, 

 to all appearances as succulent as the living roots upon which were 

 reared the 1913-1915 phylloxerse, which averaged about a 25-day 

 period, under a temperature averaging 4^° in excess of that obtain- 

 ing in the cellar in 1911. It would be natural to ascribe the faster 

 growth in the cages to the higher temperatures, but in view of the 

 discrepancies noted above in connection with the 1913 cellar and 

 incubator observations, the writers are inclined to believe that the 

 living roots afforded better nourishment to the phylloxerse than did 

 the severed roots of 1911 and that the higher temperatures of 1913 

 had less influence than might appear in bringing about such a dif- 

 ference in the growing periods. 



Excepting for a few isolated instances, the phylloxerse on living 

 roots developed more rapidly on nodosities and tuberosities than on 

 the normal surface of the root. On nodosities development was the 

 most rapid, noticeably more rapid than on tuberosities, and the more 

 fleshy the swelling the more rapid was the aphid's growth. 



DESCRIPTION OF STAGES. 



The egg. — When first laid, the radicicole egg (Pis. VIII, g ; IX, 

 k, I) is lemon yellow, about twice as long as wide, oval, both ends 

 rather bluntly, rounded, the micropylar end a little more abruptly 

 so. Thirty-six eggs laid by newly matured adults August 30 and 

 September 6, 1911, averaged 0.348 mm. in length and 0.173 mm. in 

 width, with maxima, respectively, of 0.36 and 0.18 mm., and minima, 

 respectively, of 0.34 and 0.17 mm. Of 25 eggs laid by overwintered 

 radicicoles near the end of their laying period, the maximum length 

 was 0.32 mm., the maximum width 0.18 mm., the minimum length 0.20 

 mm., and the minimum width 0.12 mm., the average length 0.26 mm., 

 and the average width 0.14 mm. Thus it appears that the size of the 

 eggs laid by individuals decreases toward the end of their egg-laying 



