76 
BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 
Table XXVI. — Measurements of the winged migrant of the grape phylloxera, 
Walnut Creek, Calif. 
1 
2 
3 
4 
5 
. 6 
8 
Length 
Mm. 
1.101 
.428 
.333 
Mm. 
Mm. 
Mm. 
Mm. 
0.906 
.317 
.309 
.0320 
.0366 
.1741 
.0536 
.0214 
.0250 
.1848 
. 2062 
.229 
Mm. 
Mm. 
Mm. 
0.900 
Width (abd. see. 3) 
.390 
Width (thorax) 
Ant ennal joints, length: 
0. 0384 
.0402 
.1902 
. 0562 
. 0268 
.0286 
.1901 
.2179 
0.0375 
.0393 
.1809 
. 0634 
. 0304 
.0269 
.1802 
.2250 
0.0321 
.0304 
.1777 
. 0241 
".'isoo' 
.1643 
0.0393 
.0384 
.1946 
.0589 
.0304 
.0277 
2 
0.063 
.0275 
.0297 
.033 
3 
.207 
Antenna! joint 3, base to apex of basal 
sensorium 
Antennal joint 3, length of basal sen- 
sorinm 
Antennal joint 3, length of apical sen- 
sorium . . . 
Hind femur, length 
Hind tibia, length 
Beak, length 
Wing expanse 
2.73 
The prenymphal instar is passed in three or four days, in the same 
time in which the corresponding instar of the wingless radicicole is 
passed. The nymphal instar, however, is relatively longer than the 
corresponding instar in the wingless form, and it is because of this 
fact that the migrant takes longer to mature than does the contempo- 
raneous wingless radicicole. The nymphal or pupal instar occupies 
from 5 to 12 days, the average being about 8 days. 
The nymphs take more food than does the corresponding wingless 
form, and after they have left a nodosity or tuberosity upon which 
they have been feeding, the lesion rapidly decays unless other in- 
dividuals are settled upon it. The nymphs do not usually move 
much during their period of growth, but if disturbed they move 
quickly and display a negative phototropism when suddenly exposed 
to light. The newly molted nymphs, however, often wander about 
with apparent aimlessness. The full-grown nymphs just before 
molting ascend the roots, seeking the surface, and transform on the 
trunk or else find their way along the root until they come to a crack 
in the soil, and crawling up the sides of the crack transform near the 
surface. In glass sections cages, wherein the glass plates did not fit 
very tightly to the soil, the nymphs were found sometimes crawling 
up to within 2 or 3 inches of the surface and sometimes transforming 
close by the roots as much as 17 inches below the soil surface, the 
resultant winged aphids being compelled to find their way to the 
surface. It was concluded that owing to the loosely fitted glass 
plates of the section cages, which allowed abnormal light to penetrate 
below the surface of the soil, the nymphs did not wait to ascend to- 
ward the surface, but transformed below, their transformation being 
governed by the strength of the light rays to which they were sub- 
jected. It may be said that these section cages measured 9 by 24 
inches, outside measurement, and allowed of a thickness of half an 
