118 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 



also to stand on the surface of the soil about its stem. Examination 

 of the piece of severed root after the experiment was concluded 

 showed that about 40 eggs and young had been washed off. Five of 

 the adults suffered no injury from exposure nor did most of the 

 remaining young and eggs. On July 12 the Catawba vine was found 

 to bear a strong nodositous infestation. On June 6, for eight hours, 

 two pieces of severed roots bearing a total of about 200 phylloxera? 

 were subjected to a similar stream of water which subsequently flowed 

 6 feet to a sound Mission vine. On- the severed roots the majority 

 of aphids were not washed off. In this instance the roots of the living 

 vine were not bared, and there were no cracks on the surface of the 

 soil around it. On July 27 this vine was examined and found to be 

 uninfested. The third experiment took place July 29. For eight 

 hours two pieces of severed roots bearing a total of about 250 phyl- 

 loxerse were subjected to a stream of water which subsequently flowed 



10 feet to a sound Feher Szagos vine growing in a pot. The surface 

 soil in this pot had been previously watered, and thus was cracked. 

 After the experiment was concluded, it was found that very few of the 

 phylloxera? had been carried off the severed roots. September 16 the 

 vine was examined, but it proved to be quite uninfested. In each of 

 these three experiments a fine stream of water was used and the angle 

 of declivity was slight. In the first experiment only, wherein the 

 roots of the living vine were actually exposed to the stream of water, 

 did an inoculation through water agency occur. It is evident, how- 

 ever, that diffusion may occur by means of water-borne phylloxera?.. 

 In the California vineyards such a condition could arise normally 

 only between November and May, for in the other months it is very 

 rare to have rain in any abundance. In April and May, however, 

 when the phylloxera? are active, heavy rains occasionally occur, and 

 sometimes on the hillside vineyards deep waterways are formed, 

 exposing the roots of vines to a depth of more than a foot. 



In this connection some laboratory experiments were made upon 

 the resistance of eggs and larva? to water exposure. For this pur- 

 pose small-sized glass vials and distilled water at about 64° F. were 

 used. In one instance, in a corked vial, 9 out of 12 eggs hatched 

 from 2 to 10 days after they were placed in the water. All those 

 that hatched remained on the surface, while those that failed to 

 hatch went to the bottom of the vial. In another instance eight 

 recently deposited eggs were placed on the surface of the water in 

 an uncorked vial. Six days later all had sunk to the bottom, but 

 subsequently hatched. In a third experiment 11 well-advanced eggs 

 were placed on the surface of the water in an uncorked vial. After 



11 days all the eggs had hatched, six having remained on the surface 

 and five having sunk to the bottom. In all three experiments the 

 hatched larva? failed to fasten to pieces of roots provided for them. 



