6 



BULLETIN 111, U. S. DEPARTMENT OF AGRICULTURE. 



It is evident that the entire girdling of about 0.5 per cent of the 

 older infested trees is accomplished by more than one larva which 

 happen to infest these trees at one and the same time. Each larva 

 evidently tries to get as far away from its neighbor as it can, and 

 thus the tree is girdled. But, as indicated, plural infestation is rare. 

 To test this point experimentally the writer has several times planted 

 in captivity two larvae on one piece of wood, and invariably one of 

 them left the sustaining slab. On a few occasions when, because 







Hiii 



.Fig. 3. — A lodgepole pine tree infested by the sequoia pitch moth. The new , flowerlike exudation 

 indicates present infestation. (Original. ) 



none vacated, the writer supposed he had made a success of "double 

 planting," he found later that one of the larvae was dead. 



Tunnels in trees infested only the second year, as well as those in 

 trees that have been infested by several successive generations of the 

 insect, look as if they had been engraved by the larvae eating the 

 wood, but such is not the case. The appearance is caused by the 

 larvae preventing the wood from forming a new layer across the 

 tunnel. Thus the tunnel, in the course of many seasons, gradually 

 becomes deeply embedded in the wood tissues. 



In rare cases the tunnel is slightly slanting, running on one side of 

 the center, a few inches below the surface of the ground, while the end 



