36 



THE GRAPE ROOT-WOEM. 



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 iDose, porous soils, and especially on 

 exposed ridges in the vineyards. (Table XII; fig. 14.) 



Table XII. — Occurrence of larvse 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. 



1907.. 



1908. 



1909. 



fMav 13-June8. 

 [May 31 



rMay 18-June ' 

 [June 12 



fMay 24-June25. 

 |Mavl9-June25. 

 May27-Julyl0. 

 Uunel-July 10.. 



Total 



Number 





Number 



number 



of vines 



Soil. 



of larvae 



of larvae. 



examined. 





per vine. 



831 



66 



Gravel . . 



12 



1 



7 



Clay.... 



0.1 



96 



14 



Gravel.. 



6 



3 



3 



Clay.... 



1 



539 



88 



Silt a ,,. 



6 



439 



83 



Gravel.. 



5 



102 



37 



Loam... 



3 



20 



54 



Clay.... 



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. 



