22 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



found that the beetles were unable to force their way out of the ground 

 when it was covered with a hard, uncultivated crust, such as is left 

 after rain on clayey soils. Each of six vines was covered on May 4th 

 with a cage of mosquito netting. In three of these cases the netting 

 was tied tightly around the lower part of the stem, as shown in figure 16, 

 in order to prevent the possibility of any beetles getting on to the 

 above-ground portion of the vine. In the other three cases the netting 



was brought down 

 to the ground, 

 enclosing about 

 three square feet 

 of soil surface in- 

 side the cage, as 

 also shown in 

 figure 16. This 

 enclosed surface 

 remained unculti- 

 vated until about 

 the middle of 

 July, when the 

 cages were re- 

 moved. 



No beetles were 

 found at any time 

 on any of the 

 six enclosed vines, 

 and no signs of 

 their attacks on 

 leaves, fruit or 

 other above- 

 ground portions. 

 This is easily ex- 

 plained in the 

 case of the vines 

 which were com- 



FIG. 17. A single vine as shown in figure 16. 



pletely shielded from attack by tying the netting around the stump ; 

 but in the case of the other vines which were exposed to any beetles 

 which might emerge from the soil within eighteen inches from the 

 stump, the only explanation seems to be that the beetles were unable to 

 force their way through the compacted surface crust. That the pupa^ 

 and beetles were abundant in the ground was shown by the fact that 

 all the uncovered vines next to those which were covered were badly 

 infested by the beetles and showed abundant evidences of their attack 

 on all parts. 



