36 
THE GRAPE ROOT-WORM. 
feeding may even extend to the underground portion of the stem. 
Most of the larvae are found within a distance of from 2 to 3 feet of 
the crown of the vine, and at a depth varying with the root system 
of the vines and the character of the soil. 
The rate of growth of the larva varies under different conditions. 
The time of hatching, the abundance of food, and the ease with which 
food can be obtained are determining factors. As a rule the larvae 
are found more abundantly in loose,- porous soils, and especially on 
exposed ridges in the vineyards. (Table XII; fig. 14.) 
Table XII. — Occurrence of larvae of the grape root-worm in different soils. Summary 
of field diggings for 1907, 1908, and 1909, at North East, Pa. 
Year. 
Date of digging. 
Total 
number 
of larvae. 
1909. 
|/May 13-Jurie 8 ! 831 
\May31 1 1 
fMavl8-June9 96 
\Junel2 3 
(May 24-June 25 1 539 
I May 19-June 25 439 
May 27-JuIy 10 102 
June 1- Jul v 10 ' 20 
Number 
of vines 
examined. 
Gravel. . 
Clay 
Gravel. . 
Clay 
Silt a ... 
Gravel. . 
Loam . . . 
Clay 
Number 
of larvae 
per vine. 
6 
1 
6 
5 
3 
0.4 
a Very light porous soil. 
From rearing and field observations we have found that the larvae 
are less abundant and slightly retarded in their development in clay 
soils. This is natural in that the larvae can not move about to obtain 
food in this soil so readily as in soils of looser texture. 
The growth of some larvae is sometimes delayed to such an extent 
as to hinder them from transforming at the normal period in the 
spring. Hence these belated larvae remain an additional year in the 
ground and transform in the spring of the second year. The causes 
of delay in the development and the percentage of belated larvae 
have been described in detail on pages 41-44. 
WINTERING OF THE LARVA IN AN EARTHEN CELL. 
As the time for hibernation approaches the grubs penetrate deeper 
into the ground, generally slightly below the roots of the vines. An 
earthen cell is made in which the larva spends the winter. It was 
observed in the field in the fall of 1909 that the 2-year-old larvae, 
referred to above, were the first to hibernate. Some of these were 
already in the wintering cells by the middle of August, when most 
of the larvae of the new brood were still extremely small or had not 
yet hatched. In Table XIII is shown the relative occurrence of 
larvae in wintering cells in the different vineyards. The actual 
percentage is higher than given, because in the process of digging 
many cells were broken, and thus escaped being noticed. 
