50 THE GKAPE ROOT-WOKM. 



vations with field conditions, and whenever differences have occurred 

 corrections in the summary (fig. 23) have been made to approximate 

 field conditions. 



SUMMARY OF LIFE-HISTORY STUDIES OF THE GRAPE ROOT-WORM. 



The life history of the beetle (see fig. 12, p. 23) may be briefly sum- 

 marized as follows: The grape root-worm produces only one genera- 

 tion a year;, the larva feeds on the roots of the grapevine, and in this 

 stage the insect is found in the ground for the greater part of the year. 

 In early June the full-grown larva makes an earthen cell a few inches 

 below the surface of the ground, within which it pupates about the 

 middle of June ; the pupal stage lasts generally twenty days, and the 

 beetle or adult begins to emerge from the ground in late June or early 

 July, while a few belated beetles continue to appear in the early part 

 of August. On an average the beetle feeds for from 10 to 13 days on 

 the grape foliage before ovipositing. The eggs are laid beneath the 

 loose bark on the canes of the vines, and hatch on an average in 12 

 days; the young larva drops to the ground and soon finds its way to 

 the roots of the vine ; generally the larva becomes three-fourths grown 

 and sometimes attains its full growth in the fall. Previous to win- 

 tering it penetrates deeper into the ground, below the roots, and there 

 constructs an earthen cell in which it passes the winter. 



The diagram (fig. 23) shows the relative occurrence and the time of 

 transformation of the grape root- worm in its various stages. It has 

 been prepared from field observations and rearing records of 1909 and 

 is a summary graphically presenting the life-history studies. 



Local variations in the times of development of the different stages 

 of the insect, as described in preceding pages, may be brought about 

 by various factors, such as differences in the texture of the soil, rela- 

 tive abundance of food, and altitude and exposure of vineyards. 

 The seasonal variations, as shown by the difference in the time of 

 emergence of beetles during 1907, 1908, and 1909, and also by the 

 occurrence of larvae that remained two winters in the soil, are the 

 direct results of climatic influences. The insect has a strong tendency, 

 however, to develop normally, even under adverse conditions. 



NATURAL ENEMIES. 



PREDACEOUS INSECTS. 



Several predaceous insects have been found feeding upon the larvae 

 of the grape root- worm. During the process of digging for larvae, 

 both in the spring and fall, various species of carabid beetles and their 

 larvae have been found in the ground. These insects are entirely pre- 

 daceous and probably feed upon the grubs of the grape root-worm 

 whenever the latter come within their reach. Dr. E. P. Felt recorded 



