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



METHODS OF REARING THE RADICICOLE LARV^. 



During 1911 and 1912 the radicicoles were reared exclusively, both 

 within and without an electric incubator, in the cellar. The roots 

 on which the phylloxerse were reared were kept in glass jars and in 

 petri dishes with moistened filter paper. This method was not always 

 satisfactory, since it was not easy to maintain an even humidity 

 similar to that existing under natural conditions. 



In 1913, 1914, and 1915 the insects were reared in the cellar and in 

 the cages described below. The jars in the cellar were moistened by 

 a layer of wet sand placed in the bottom. This method was more suc- 

 cessful than in the case where moistened paper was utilized ; the roots 

 did not decay or dry up so rapidly, and they remained in much bet- 

 ter condition through the winter. 



These cages (Pis. V; VI, fig. 1; VII), constructed to hold young 

 vines, may be described as follows: A trench 3 feet deep was dug 

 wide enough to hold the cages with a space about 1 inch wide on each 

 side. To prevent air passing down the cracks, small blankets were 

 laid across the spaces, and this resulted in a temperature inside the 

 cages of scarcely greater fluctuation than normally occurred 2 feet 

 underground. The cages themselves were made of paraffined pine 

 with an extra redwood bottom, and had two compartments, one above 

 the other (PI. VII). The upper compartment had on each side one, 

 and the lower two, detachable boards the whole length of the major 

 sides, and these boards were detachable to permit examination of 

 of the roots and the removal of the pots. The upper compartment 

 contained one and sometimes two pots (8 or 9 inches in diameter), 

 around the top of which was fitted the topmost board of the cage, the 

 outside measurements of which were 22 by 13 by 27 inches. The 

 lower compartment contained 9-inch pots in saucers. 



The method of planting the vines in the pots of the cages was as 

 follows : Into the middle board of the cages were fastened one or two 

 saucers having holes bored through them. A short piece of glass 

 tubing larger inside than the diameter of the roots was fixed into 

 these holes with a cone of paraffin. Two half pots, bottomless, were 

 bound together by wire or tin bands to make a single whole pot, and 

 placed to rest on the saucer. The vine was then put in place, certain 

 of its roots being passed through the holes in the saucer and protrud- 

 ing below. The upper pot was then filled with soil with a thin top 

 layer of fine sand. In the lower compartment, whole 9-inch pots, one 

 or two, as the case might be, were put in place in their saucers, and 

 the protruding roots planted in them, at the surface of the soil 

 passing through about 3 inches of glass cylinder. The surface of 

 the soil in the lower pots was covered in most cases with a thin 

 layer of fine sand. Fine sand was tamped into the glass cylinders, 



