THE GKAPE PHYLLOXERA IN CALIFORNIA. 113 



from which wanderers were issuing. It is true that the soil surface 

 inside the cans was a small area — 126 square inches — and that the 

 soil itself was not as thoroughly cracked as it might have been ; but 

 in many instances the cans were not more than 1 foot from the 

 trunks of the infested vines, therefore, from the wanderers when 

 they issued, whereas in vineyards vines are set 6 or more feet apart. 

 (2) The presence of cracks in the soil leading directly to roots is 

 necessary to permit the wandering larvae to descend to roots, for the 

 larvae can not dig their way through the soil, and during the period 

 when they are issuing, rain, which might provide moisture to draw 

 them into the soil or wash them onto exposed roots, is lacking. 



The writers are of the opinion that wandering larvae are the cause 

 of considerable local spread of phylloxera, that is, within the vine- 

 yard or district; and that they are instrumental in causing the 

 formation of new phylloxera " spots " or foci. Under favorable 

 conditions it has been proved that they may live for at least three 

 days above the surface of the soil, and thus may be transported 

 from place to place with the possibility of finally becoming located 

 on a vine root. There is no reason why wanderers may not live for 

 as long as two weeks on the soil surface without feeding, provided 

 this surface is not heated by the sun. In one instance, after being 

 placed on a piece of root, several of them wandered for as many as 

 five days before settling down to feed. It may be said also that 

 larvae have been found to live in water as long as nine days without 

 food, and it may thus be assumed that they might remain as long in 

 the open air under average conditions of temperature and humidity. 

 This fact would explain how the insect may be spread from one 

 locality to another by wandering larvae that lodge in such vine 

 material as picking boxes (see following under " Casual agencies of 

 diffusion," p. 115). 



There are certain marked instances in California vineyard dis- 

 tricts where phylloxeration has developed " with the prevailing 

 winds." The only wind-borne forms of the phylloxera in California 

 are the winged migrants and the wandering larvae. The California 

 biology indicates that the migrant has no bearing on the preserva- 

 tion of the species, and therefore such phylloxeration has resulted 

 from wind-borne wandering larvae. 



DIFFUSION BY NEWLY HATCHED RADICICOLES TRAVELING THROUGH THE SOIL. 



In 1914, experiments on subterranean diffusion were conducted. 

 In April three Muscat rooted vines were planted in a 4-foot square box 

 containing heavy loam covered with a 3-inch layer of fine sand. The 

 sand was used for the purpose of preventing wandering larvae from 

 emerging upon the surface and reaching the sound vines. May 20, 

 1900°— 21 8 



