THE HOMOPTERA 203 



During the latter part of this second season some winged forms (Fig. 194) 

 are produced and these make their way up to the surface of the ground and 

 migrate to other vines where they lay eggs. These produce both male and 

 female plant lice and each female lays a single fertilized egg which winters over. 



This 2 -year life and the production of leaf galls is not always necessary to 

 the continued existence of the insect however. The root form generally goes on, 

 brood after brood, particularly on the European grape, without the formation 

 of leaf galls, and while young from the leaves may probably pass to the roots 

 at any time during the summer, the migration of root forms to the leaves is 

 unknown. Apparently then, the life history just outlined applies to American 

 varieties of the vine, but in the case of the European species, while the lice may 

 pass to the roots they do not usually, at least, seem to migrate in the reverse 

 direction, the insects coming from fertilized eggs passing directly to the roots. 

 Root forms may spread to other plants through the soil. 



Control. Four methods of control have been made use of for this pest, viz., 

 the injection of Carbon disulfid into the soil close to the roots; flooding the vine- 

 yard with water; planting in very sandy soils; and the selection of resistant 

 varieties. The first of these has given fair results where the soil is loose, deep and 

 rich, but is most successful in cooler locations, and here the insect is least abun- 

 dant. It is also rather expensive and has therefore largely been replaced by other 

 treatments. 



Submersion of the ground under water is a better method, but obviously 

 cannot be made use of in most cases. The vineyard must be kept covered with 

 at least six inches of water in order to drown the lice and unfortunately the best 

 time to do this is during the summer when the vines are most liable to be injured 

 by this treatment. The time chosen therefore, is after the vines have stopped 

 active growth but before the lice have become dormant. In California this is 

 generally some time in October. Flooding then should last from a week to 

 10 days: later in the season it must be extended and in the winter months 35 

 to 40 days of treatment is necessary. 



Planting in sandy soil is, for some reason not understood, a protection of the 

 vines against Phylloxera, particularly where it contains a high percentage of 

 siliceous sand. It is not always possible to locate vineyards on such soil however. 



The selection of resistant varieties of the grape is now the favored method of 

 control. With such varieties the insects when present on the roots do not in- 

 crease rapidly and the diseased tissue of the swellings on the roots does not go 

 deeper than the bark, leaving the roots proper quite healthy. At the present 

 time the grafting of vinifera varieties on resistant stalks which preserves the 

 resistant properties of the roots while producing the vinifera quality of grapes 

 so much desired, seems to give the best results in vineyards, though the proper 

 combination of different varieties of the two calls for a detailed knowledge of 

 the subject in actual practice. 



The Corn Root Aphis (Aphis maidi-radicis Forbes). This insect, though it 

 can hardly be regarded as universally distributed through the United States, 

 is both a serious pest of corn over a large area and because of its interesting rela- 

 tion with ants, an interesting species. It appears to occur throughout the 

 eastern United States as far west as South Dakota and Colorado and south to 

 South Carolina, Louisiana and Texas, but its destructive work mainly covers the 

 territory from New Jersey to South Carolina and west to the Mississippi River. 



