THE GRAPE PHYLLOXERA IN CALIFORNIA. 95 



the. existence of the gallicoles in Arizona under dry climatic condi- 

 tions appeared to disprove this theory. At present it is held that 

 the phylloxera in California is undergoing, and since it was first 

 introduced (about 60 years ago) has continuously undergone, a 

 marked change in habits resulting from variations in the character 

 of its food. Wherever the phylloxera is attacking vinifera vines its 

 habits are undergoing change. In many localities the production of 

 sexuals, winter eggs, and gallicoles proceeds simultaneously with 

 prolific agamous radicicole infestation, and in such places speedy 

 diffusion of the species obtains by reason of the winged insects and 

 gallicole in addition to the wanderers. In California and in certain 

 other localities the spread of the phylloxera has been slow, primarily 

 because the danger from the agencies of the migrants and gall in- 

 habitants has been very slight, and this notwithstanding the presence 

 of resistant vines, the type on which the gallicoles normally form the 

 galls and on which the " winter " eggs develop the more successfully. 

 Thus it appears that the phylloxera, since it has been in California, 

 has modified its habits to suit its environment, by exchanging the 

 complicated life cycle on its native plants (native vines of eastern 

 North America) for the more simplified life cycle upon Vitis vini- 

 fera. 



THE GALLICOLE AND ITS RELATION TO CALIFORNIA CONDITIONS. 



In the eastern United States, in Arizona, and in the majority of 

 the phylloxera districts in Europe the gall form or gallicole occurs. 

 This is most prevalent in the more humid districts, and occurs chiefly 

 on American vines and American hybrids and only rarely on Vitis 

 vinifera and its hybrids. Recent research in European countries, 

 especially in Italy by Grassi and his colleagues, has proved that 

 the original gallicole hatches from the winter egg deposited during 

 the previous autumn by the sexed female in a crevice in the bark. 

 This larva hatches with the appearance of the first leaves and 

 attaches itself to the surface of a young leaf, where its punctures 

 produce a "pocket" formation in the leaf tissue. In this pocket it 

 grows, matures, and deposits its eggs. Upon hatching, the resultant 

 larva? seek young leaves higher up on the growing cane, and, settling 

 on the surface, cause further pocket formations. Succeeding gen- 

 erations follow throughout the summer, the numbers being more and 

 more reduced by predacious enemies (Syrphidae, Agromyzidae, Coc- 

 cinellidae, etc.) , and also by a certain percentage of the newly hatched 

 larva? deserting the cane for the roots. Among the later genera- 

 tions the percentage of larva? that seek subterranean existence in- 

 creases, and such larva? may be differentiated by certain character- 

 istics, when newly hatched, from those destined to continue on the 

 foliage. They possess relatively longer beaks and a different anten- 



