THE GRAPE PHYLLOXERA IN CALIFORNIA. 
67 
Table XVIII. — Measurements of fourth-instar radicicoles of the grape phyl- 
loxera, Walnut Creek, Calif. 
Individual No. 1 
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- 
sor ium. 
1 
2 
3 
1. .. 
Mm. 
0.919 
.851 
.824 
.615 
Mm. 
0.517 
.528 
.579 
.500 
Mm. 
Mm. 
0. 0848 
Mm. 
0. 0687 
Mm. 
0. 0321 
.0321 
.0276 
. 0306 
.0297 
Mm. 
0. 0259 
.0277 
.0241 
.0261 
.0248 
Mm. 
0. 0669 
.0571 
.0768 
.0748 
.0721 
Mm. 
2. .. 
3... 
.0830 
.0749 
0. 0212 
4 
0.172 
.162 
.160 
.0167 
5... . 
.0162 
6... 
.753 
.700 
.426 
.0802 
.0671 
7 2 
1 Individuals 1-3 were measured toward the end of the instar, and individuals 4-7 very shortly after 
molting. 
2 Maximum height, 0.3 mm. 
A very obvious growth takes place during the fourth instar (PL X, 
g-j). At the end of this instar the phylloxera casts its last skin 
and issues therefrom as an adult. The adults, except immediately 
following the molt, are never as pale as the immature forms. They 
may be distinguished from fourth-instar individuals by two longi- 
tudinal furrows on the thorax and by the relatively larger dorsal 
tubercular areas. The color varies from a light green to a dark 
purplish brown in living specimens. This variation is to a great 
degree dependent on the food supply. On fresh, fleshy nodosities 
the insects mostly are pale green with the tubercular areas very 
noticeable. On tuberosities, or on the normal surface of a vigorous 
root, the color is yellowish green, olive green, or light brown, with 
the tubercular areas often less evident. 
On roots of poor quality the adults are brown or orange and the 
tubercular areas hardly perceptible to the naked eye. After weeks 
of egg production old adults become brown or purplish brown. In 
shape the adults while not engaged in egg laying are hemispherical 
or short oval, about equally rounded at either extremity, but while an 
egg is being passed the insect assumes a pyriform shape and the 
caudal end is much tapered and extended. 
Mature radicicole. 
PI. IX, a, b, c. 
Color varying: from pale green and pale yellow to deep purplish brown, de- 
pendent on character of food and age of individual; shape hemispherical, 
short oval, pyriform while passing the ova; body obscurely glabrous, often 
appearing to be coated on the dorsum with a very fine whitish powder; under 
side of abdomen paler than upper. Body about twice as long as wide, widest 
at middle of mesothorax ; highest at about cephalic third ; body flattening both 
cephalad and caudad from this point. Head with dusky central area; eyes 
dark red, each composed of three circular facets, arranged in form of an equi- 
lateral triangle; antennae pale, not quite reaching posterior margin of head, 
composed of three joints, of which the two basal are subequal in length but 
