THE GRAPE PHYLLOXERA IN" CALIFORNIA. 29 



upper side of the leaf; (2) several parthenogenetic generations to 

 which the stem mother gives rise, some of which settle on the foliage 

 and produce new galls, as gallicoles, while others repair to the roots 

 and settle on them as radicicoles; (3) parthenogenetic generations 

 on the roots descended from the phylloxera? which went from the 

 foliage to the roots; (4) winged migratory forms, comprising a very 

 variable percentage of the root and gall forms, produced in summer 

 and autumn, which fly or are transported by wind to other vines and 

 oviposit either under the bark or on the leaves; (5) the true sexes, 

 which are wingless and beakless; (6) the winter egg, deposited under 

 the bark by the sexed female after coition; (7) radicicoles, born on 

 roots in the late autumn, which pass the winter thereon as small 

 hibernants, mature the spring following, and give rise to radicicole 

 generations which succeed one another during the summer and 

 autumn. This, briefly, is the life cycle that occurs in parts of 

 Europe where American vines are used for stock, and in the eastern 

 and southern United States on the wild grapes and on varieties de- 

 rived from them. 



It will be observed that the winter may be passed in two forms — 

 the winter egg and the hibernant, the former on the aerial and the 

 latter on the subterranean or root portion of the vine. On certain 

 wild grapes, as Vitis riparia, V. rupestris, and V. herlandieri, and on 

 hybrids from these species, the former is the normal form, and hiber- 

 nating larva? are rare. On species like Vitis labrusca, V. monticola, 

 and their derivatives, both forms may occur. On vinifera? (Vitis 

 vinifera) the latter form is by far the more common. In the 

 majority of European grape districts both forms occur, the former 

 on American resistant vines and the latter on vinifera?, but in other 

 localities, even where resistant vines are used, the winter egg is very 

 scarce. These include certain regions of France and California, and 

 it appears that in California the hibernant is normally the only form 

 that passes the winter. 



The suppression of the winter egg, and, therefore, of the succeeding 

 gall form, brings about a modified life cycle in the California vine- 

 yard which may be briefly described as follows: (1) The hibernant 

 radicicole passes the winter as a larva on the roots and occasionally 

 on the trunk beneath the bark. (2) The hibernant, when mature, 

 gives rise to generations of radicicoles, and the aphids that issue 

 from eggs in late autumn become hibernants. (3) A certain per- 

 centage of radicicoles, varying from causes such as humidity, tem- 

 perature, condition of food, and variety of vine, develop into winged 

 migrants and issue from the ground. (4) Radicicole larva? forsake 

 the roots and seek to reach other vines either by way of the soil 

 surface or through subterranean passages such as cracks. 



