104 



BULLETIN 903, IT. S. DEPARTMENT OF AGRICULTURE. 



Wanderers were first caught on sticky papers July 21 and first ob- 

 served alive in the vineyard August 11. After August 18, no more 

 were caught on the sticky papers, and after August 25, no more were 

 observed alive. The weather during July and August was for the 

 most part bright and warm. In the vineyard the wanderers were 

 observed in by far the greatest abundance near the trunks of the 

 vines, and it appeared that they had reached the soil surface by fol- 

 lowing up the roots. No wanderers were observed on the aerial 

 portions of the vines themselves. They showed much activity, wan- 

 dering aimlessly around over the soil. They seemed to prefer the 

 shaded parts, but appeared also on ground surface exposed to the sun. 

 Large numbers were found dead close to the vine trunks, and these 

 occurred in places where the soil was very fine, indicating that the 

 phylloxeras were unable to progress in fine soil. Laboratory ex- 

 periments bore out this supposition. Many others became caught 

 in spider webs stretched over the soil surface. The character of the 

 soil in the vineyard in August, 1914, was such as to enable phylloxera? 

 to pass from one vine to another without necessarily encountering 

 very fine soil, as no cultivation had been practiced since May, 1914, 

 and the vineyard had been cultivated previously only in one direction. 



As regards the capture of wandering larvae upon sticky papers, 

 the data {riven j n Table XXXIV are of interest : 



Table XXXIV. — Wandering larvos of the grape phylloxera ; diffusion in vine- 

 yard: Walnut Creek, Calif., 191',. 



Date caught on paper. 



Number of ' 



wandering 



larvae caught. 



Distance 

 from nearest 

 vine trunk. 



Area of 



sticky paper 



on which 



phylloxera 



were caught. 



July 21-24 



3 

 1 



20 

 1 

 2 



i 



1 



Fee'. 



5 

 2 

 2 

 5 

 2 



2' 



Square inches. 

 135 



July24-2S 



135 



July 31- Aug. 3... 



135 



Do 



135 



Aug. 7-11 



135 





135 



Aug. 14-18 



135 







During the period from July 21 to August 18 many sheets of 

 sticky paper 135 square inches in area (9 by 15) were placed on the 

 surface of the ground, and wanderers were caught on 7 (see above) out 

 of 32 papers. In the majority of instances the individuals were caught 

 on the side of the paper tow T ard the nearest vines, Avhich would indi- 

 cate that they arrived there straight from the trunk of the vine. On 

 sides of the paper facing vines farther away it would be natural 

 to expect fewer wanderers when one considers how the circum- 

 ference of a circle increases in proportion to its radius, and also the 

 comparatively equal diffusion of wanderers in all radii, if the vine 



