THE MONTHLY BULLETIN. 



443 



the insects on a tiny fibrous root embedded within. It is this habit of 

 working on the fibrous roots and destroying the feeders that makes the 

 pest possibly more dangerous on pear than on apple, and also accounts 

 for the fact that it has been little observed. 



DEPTH IN SOIL. 



It is often claimed that woolly aphis of the apple affects only the 

 roots close to the surface. The writer's experience with the pest in 

 Colorado — partially at least — bears out this contention. With the pear 

 it had been found in a Placer County orchard at a depth of three feet 

 — in fact just as deep as any fibrous roots could be found in this case. 

 The soil in the particular orchard where this observation was made, 

 was quite heavy with a tendency to bake. The fact of its occurrence 



Fig. 95. — Bartlett pear tree in same row as Fig. 94, with a bad infesta- 

 tion of woolly aphis on the roots. (Original.) 



SO deep in the soil, coupled with the other important one mentioned, 

 viz : the general distribution throughout the soil area of orchards indi- 

 cates the impossibility of any soil treatment being made effective. 



AERIAL COLONIES. 



It is seldom that aerial colonies of woolly aphis are seen on pear 

 trees. These have been noticed by the writer in only three orchards — 

 one at Grand Junction, Colorado, and the other two in Santa Clara 



