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 
larvae 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, Agromyziclae, Coc- 
cinellidae, etc.) , and also by a certain percentage of the newly hatched 
larvae deserting the cane for the roots. Among the later genera- 
tions the percentage of larvae that seek subterranean existence in- 
creases, and such larvae 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- 
