106 BULLETIN" 903, U. S. DEPARTMENT OF AGRICULTURE. 



the end of the third week in August. The condition of the soil was 

 about the same in both years, moisture being somewhat higher than 

 usual because of extra heavy precipitation each spring. The reten- 

 tion of moisture near the soil surface tends to produce many fleshy 

 rootlets, and these in turn produce abundant nymphs and wandering 

 larvae. Thus a wet spring results in the early production of migrants 

 and wandering larvae. 



A number of laboratory observations were made on the wandering 

 larvse. From these it appeared that the insects were capable of 

 walking as much as 14 feet on a smooth surface, provided a strong 

 light attraction was present. On fine soil their appendages became 

 clogged very soon, and prevented further locomotion, but on hard 

 surfaces, they progressed successfully. On warm surfaces they easily 

 became " baked " to death, and in fact always lived the longest when 

 least exposed to the sun, as the heating of the surface soil killed the 

 aphids. Larvae easily passed over wet sand and were able to make 

 headway on dry sand, but could not penetrate sand. It was found 

 that the larvse could remain alive at least for three days, wandering 

 around partly upon the soil and partly in cracks in the soil in a 

 flowerpot subjected to an average amount of direct sunlight. 



During the summer and autumn of 1914 a number of young rooted 

 vines were planted in 9-inch pots, and these were inoculated during 

 May and June by burying phylloxerated roots around the stalk or by 

 transferring eggs to the larger roots. These vines included viniferae, 

 American nonresistants, and resistants. On the top of these pots 

 and resting on the earth were fitted tightly circular pieces of wood 

 with a hole in the center, through which passed the stalk of the 

 vine. The whole aerial portion of the vine was inclosed in a muslin 

 cage. This construction was designed to compel phylloxerae ascend- 

 ing to the soil surface to make their way through the hole around, 

 the stalk; and having done so, they would be unable to escape by 

 reason of the white muslin cage and would soon die. In October 

 and November these cages were examined, and in some of them 

 small numbers of dead wanderers were found, in others none, and 

 in still others very large numbers. Those containing dead wan- 

 derers in abundance were the ones in which the vines had been fer- 

 tilized with chemical fertilizers, and there was also a corresponding 

 abundance of winged migrants from such vines. The action of the 

 fertilizers produced many migrants and many wanderers and in- 

 vigorated the vines, yet in all cases a large root infestation by wing- 

 less forms persisted through the winter following. In the cages 

 above mentioned fertilizers, in liquid form, were applied periodically 

 during the summer. In 1915 a similar series of vines were fertilized 

 with solid fertilizers at the time of planting in early spring, and 



