68 
BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 
joint 1 wider than joint 2 : third joint about twice as long as the two basal 
combined and bearing a single oval sensorium near apex : ail three joints bearing 
hairs. Beak pale, base and tip shining and dusky, reaching to second or third 
abdominal tergite ; in specimens examined after they had transfixed the beak 
into the roots, this organ appears to be shorter, due to the telescoping of the 
sheath from the action of transfixing. 
Mesothorax largest segment of body, twice as long as prothorax, which is 
next largest ; mesothorax divided into two sections by transverse fold. Thoracic 
segments having median portions raised above lateral portions by means of 
two longitudinal curved folds. Aletathorax very similar above to any of first 
five abdominal segments. Legs in pale specimens slightly darker than abdomen. 
coxaB dusky. 
Sixth abdominal segment produced conically at each of its posterior angles 
and narrowed basally ; caudal segment twice as long as broad, bluntly rounded. 
with a small central emargination and fringed with a marginal row of pale 
weak hairs. 
The dorsum of the body bears six longitudinal rows of dusky circular tuber- 
cular areas, which under magnification appear as thickenings and roughen- 
ings of the epidermis, and each of these is surmounted by a single spine. 
Table XIX gives measurements of the adult radicicole. 
Table XIX. — Measurements of mature radicicole of the grape phylloxera, 
Walnut Creek, Calif. 
Individual Xo. 
Length 
of body. 
Maxi- 
mum 
width 
of body. 
Length 
of beak. 
Length 
of hind 
femur. 
Length 
of hind 
tibia. 
Length of antennal joints. 
Length 
of sen- 
sorium. 
1 
2 
3 
1 
Mm. 
0.854 
Mm. 
0.502 
Mm. 
Mm. 
0. 0795 
.0804 
.0839 
.0875 
Mm. 
0.07S6 
. 0759 
.0748 
.0768 
Mm. 
0.0223 
. 0252 
.0260 
.0197 
Mm. 
0. 0251 
. 0243 
.0230 
.0230 
Mm. 
0. 0661 
.0660 
.0673 
.0705 
Mm. 
0.0224 
.0195 
2 
.878 
1.011 
.997 
.942 
.783 
.778 
.763 
.734 
.714 
.712 
.686 
.631 
.582 
.549 
.584 
.558 
. 593 
507 
0.281 
.0196 
3 
4 
.0205 
5 
6 
.503 
.455 
.433 
.448 
8 .. 
1 

9 
10 
11 
.392 
.408 
.416 
.352 
12 
13 

14 
Measurements of beaks from nine adult hibernants were made 
March 18. 1915. Of these six. fixed in the root tissue, measured 0.276, 
0.243, 0.260. 0.252. 0.198. and 0.179 mm., respectively. The other 
three, not fixed since casting their last skin, measured 0.329. 0.317, 
and 0.299 mm., respectively. The basal joints of the rostrum, are 
telescoped when the beak is thrust into the root. 
It is obvious from an inspection of Table XIX that the adult 
radicicoles vary greatly in size. This variation occurs whatever kind 
of food supply the phylloxera? are getting, although the average size 
is larger on good succulent food than on that of poorer quality. Indi- 
viduals 5 to 14 in Table XIX were all taken the same day (Mar. 18) 
