468 



BULLETIN 388 



I 



As the larvae grow, the channels become larger and the amount of frass 



is greatly increased. In order to make room for the developing larva 



the frass is forced outside the channel, by 

 small openings cut through the outer bark. 

 This is well shown in figure 118. 



The larvae become nearly full-grown before 

 they leave the cambium layer. They then 

 burrow at an angle upward into the hard 

 wood of the tree. The beginning of this 

 burrow is easily recognized, as the character 

 and quantity of the frass suddenly changes. 

 It becomes white and much larger in quan- 

 tity, and consists of small particles of the 

 wood cut off by 

 the mandibles of 

 the larva? (fig. 

 119). In Xew 

 York the forma- 

 tion of the pupal 

 channel begins 

 about June i. 

 By the middle of 

 June the majority 

 of the larvae have 

 begun their pupal 

 burrows. At this 

 time, as one looks 

 down the rows of 

 BY poplars in the 

 nursery the white, 



sawdust-like frass can be seen distinctly on the 



infested trees and on the ground beneath them. 

 In the formation of the pupal chamber the 



larva bores upward and into the heart of the 



small nursery trees. This burrow varies from 



slightly over an inch to several inches in 



length. From three to four weeks are required 



for its completion. When ready for pupation 



the burrow is solidly packed with frass, the 



pupal chamber being formed at the upper end 



(figs. 120 and 121). The larva then places itself head downward in 



preparation for pupation. 



FlG. 1 1 8. FRASS FORCED OUT 

 THROUGH SMALL OPENINGS 

 MADE IN THE BARK 

 YOUNG LARVAE 



FlG. 119. CHARACTER OF THE 

 FRASS WHEN LARVA BE- 

 GINS TO BORE INTO HEART- 

 WOOD TO FORM PUPAL 

 CHAMBER 



