THE GRAPE PHYLLOXERA IN CALIFORNIA. 
73 
phylloxera ted vines, the rising temperature, and the intrinsic vigor 
of the vine encouraging emigration. 
Apparently the young produced from the eggs deposited by over- 
Avintered females do not become wanderers, but those of later gen- 
erations may, and many wandering larvae produced late in the au- 
tumn settle on roots and hibernate. 
Wandering larvae play an important part in the diffusion of phyl- 
loxera. 
THE NYMPH AND WINGED FORM. 
DEVELOPMENT. 
The individuals which are destined to become winged are termed 
in their third instar " prenymphs " and in their fourth instar 
"nymphs." They are produced from eggs deposited by adult radi- 
cicoles, and until after their second molt differ in nowise from the 
individuals destined to remain wingless; neither is there any dif- 
ference in the eggs from which the two types hatch. In their third 
instar the prenymphs (PL X, d, e, f) differ from the radicicoles of 
that instar in that the former have more elongate and narrower bod- 
ies and longer antennae and legs. The prenymphs are generally pale 
greenish yellow, and their appendages appear quite dusky in com- 
parison. Table XXIV gives measurements of four prenymphs. 
Table XXIV. — Measurements of prenymphs of the grape phylloxera, Walnut 
Creek, Calif. 
Individual No. 1 
Length 
ofbody. 
Maxi- 
mum 
width 
ofbody. 
Length 
of beak. 
Length 
of hind 
femur. 
Length 
of hind 
tibia. 
Length of antennal joints. 
Length 
ofsen- 
sorium. 
1 
2 
3 
1 
Mm. 
0.805 
Mm. 
0.405 
Mm. 
0.357 
Mm. 
0.0948 
.0939 
.0946 
Mm. 
0. 0821 
.0839 
.0713 
Mm. 
0. 0330 
.0321 
.0306 
.0306 
Mm. 
0. 0268 
.0277 
.0279 
.0279 
Mm. 
0.0839 
.0889 
.0973 
.0919 
Mm. 
0. 0196 
.0193 
2 
.660 
.325 
.193 
3 
.541 
.555 
.300 
.284 
.186 
4 
1 Individual 1, just before molting into nymph; individuals 2 to 4, very shortly after molting into pre 
nymphs. 
The prenymph molts into the nymph or pupa. The pupa is the 
longest of all forms of the insect and is easily discernible on the 
root by the presence of wing pads, even just after it has molted from 
the prenymphal form, and has a greenish color. Immediately after 
the skin is shed, these wing pads are yellow, but very quickly they 
become gray or blackish. During the first few days of the nymphal 
instar the insect is green or greenish yellow, and the compound eyes 
are indiscernible, but as it grows it lengthens, becomes constricted in 
the region of the metathorax, and turns orange, the mesothorax, how- 
ever, remaining paler than the rest of the body. The compound 
