126 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 
The winged form is produced from the middle of June until No- 
vember. It is more abundant in the coastal districts than in the in- 
terior valleys. In their first two instars the larvae of the winged 
form do not differ from the corresponding stages of the wingless 
form, but in the third and fourth stages they differ structurally, and 
in these stages are termed, respectively, prenymph and nymph. Both 
these forms are elongate in shape and are light greenish-yellow or 
yellowish-brown. The nymphs have two pairs of grayish-black wing 
pads. The winged insect is orange in color with grayish-black head 
and thorax and two pairs of scantily veined wings. 
The nymphs transform in most instances near the surface of the 
soil and the winged migrants issue on the surface and fly about in 
the vineyard and neighboring regions. 
The winged insects deposit eggs of two kinds, viz. male and 
female, and the insects which mature from these eggs are the true 
sexes. These forms are unable to take food, and under normal con- 
ditions mate upon reaching maturity and the female forthwith de- 
posits a single egg under the bark of the vine. This egg hatches in 
spring and gives rise to a series of generations of gall-inhabiting and 
gall-making wingless aphids. A certain percentage of larvae born in 
the galls, however, migrate to the roots before taking food, and in 
this way the species returns to the soil. 
In California, under natural conditions, it is doubtful whether 
any sexes mature and still more doubtful whether any winter eggs 
hatch. Laboratory experiments indicate that the sexes mature in 
about 12 days. 
In the late autumn, along with the nymphs are found curious 
forms intermediate in appearance between adult radicicoles and 
nymphs. These are called intermediates or nymphicals. They are 
not abundant and all those whose progeny have been observed were 
parthenogenetic. 
The diffusion of the phylloxera is effected in nature by the wan- 
dering newly hatched larva? of the radicicoles during summer and 
autumn. These pass from vine to vine, either on the surface of the. 
soil or through subterranean cracks or pathways. They may also be 
borne by the wind or on vineyard material, such as picking boxes. 
Probably water is responsible for some diffusion in hilly or irrigated 
vineyards, and cultivating instruments by picking up pieces of in- 
fested roots may effect fresh infestations. The phylloxera is easily 
introduced into a vineyard or section by the practice of planting 
infested rooted vines to make up for cuttings which did not succeed 
in previous years. 
