20 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



applied to the ground to prevent the larvae from entering, but knowing 

 the results of the New York experiments 1 along this line, we gave 

 little encouragement to the idea, and did not repeat the experiments. 

 Kerosene emulsion and crude petroleum were used in New York, but 

 neither proved of any practical value. The trouble with such sub- 

 stances is that they are too readily absorbed by the dry soil and too 

 quickly evaporated. Our California crude oil, which has an asphaltum 

 base (instead of paraffine, as is the case with eastern oils), would not 

 disappear so quickly, but few farmers would want such a substance 

 mixed with their soil. 



FIG. 15. At work digging out larvse of the California grape root-worm'two 

 and one half feet beneath the surface. 



Of the Pupa. As heretofore stated, the pupa? are found at a depth 

 of from four to eight inches below the surface. This, together with 

 the fact that any disturbance of the cell in which they are resting will 

 generally prove fatal, offers a chance of doing something in the way of 

 control while in this stage. While some of them are beyond the depth 

 of the plow as ordinarily used about the vine, yet probably the major- 

 ity will be found within about six inches from the surface. They do 

 not come up to the dry soil to pupate, but remain just below it. If 

 a shallow mulch of two or three inches can be kept immediately around 

 the vines until the insects are ready to pupate, this will conserve the 



-1 New York State Museum Bulletin 59, p. 77. 



