BULLETIN 198. THE GRAPE LEAP-HOPPER. 213 



most of the hoppers came out on the open side toward the light, and 

 it was with difficulty that they could be caught on the black oiled 

 canvas. The canvas also absorbs more of the oil than the screen and 

 makes a drier surface for the hoppers to light upon, thus failing to 

 hold them as well as the free oil on the wire of the screen. 



Kerosene may be used on the screen as well as crude oil, but it 

 evaporates more rapidly and more frequent applications are necessary. 

 For a fine mesh screen, however, the kerosene works very well, since 

 it does not darken the sides so much as the black crude oil. 



The time to use this screen cage is in the early spring when the 

 shoots of the vine are not more than four or five inches long. At this 

 time all the hoppers have left their winter food plants and have begun 

 to feed upon the vines, and none have yet laid eggs. This method, 

 therefore, captures them at a critical time before they have begun to 

 breed, and thus greatly reduces the numbers of the succeeding gen- 

 erations. 



The work may also be done more easily and effectively at this time, 

 since there is not the excessive foliage that appears as the season 

 advances. The size of the vines to be treated will determine the size 

 of the cage. Ordinarily, the cage need be but very little larger than 

 the diameter of the vines after pruning. In -one young vineyard, two 

 years old, the hoppers were kept down successfully by a small cage 

 about one foot square, which was easily handled by one man. With the 

 larger cages three feet square, handles are attached to each side and 

 the cage manipulated by two men. One of these cages with two men 

 will go over four or five acres a day. There is practically no expense 

 for materials and the time of the men is the chief outlay. 



If this screen cage is conscientiously used it will capture from 85% 

 to 95% of the hoppers, and at a time in the life-history of the insect 

 when for each hopper taken it means a hundred or so less later in the 

 summer. 



This method of capturing the hoppers with the screen cage was 

 developed for vines that are headed some little distance above the 

 surface of the ground. There are many vineyards in the State, however, 

 that have not been so pruned. Some are headed directly at the surface, 

 and in some even the canes come out from the stump beneath the 

 surface, and a cone-shaped area is scooped away to make room for the 

 growth of the canes. This form, in some cases, is given to the vine 

 by frost; but where the pruning is responsible, it is generally considered 

 now to be a bad system. 



If the cage is to be used on such vines, it must be done with some 

 modification of the bottom or the bottom dispensed with entirely, though 

 this is an important part of the apparatus. 



