142 



Bulletin 234. 



but sometimes going for a short distance deeper into the wood, even to 

 the center of the branch. The borer packs the burrow behind it with its 

 excrement and wood particles which turn dark brown in the first or 

 smaller portion of the mine. The flattened grub makes a shallow burrow 

 that gradually widens to an eighth of an inch. Many of these zigzag, 

 packed burrows are shown at a in Fig. 36. 



It is difficult to follow a burrow throughout its whole length. Larsen 

 (Mich. Acad. Sci., 3rd Rept. 1902, p. 48) states that he followed one 

 " through its winding course a distance of I foot and 7 inches in a length 

 of branch of 4 inches, now near the bark, now deep down in the wood; 



Fig. Ti3- — Portion of trunk of infested white birch, showing no injury apparent 

 imLil the bark is removed and the numerous burrovas of the borer revealed. 

 Natural sise. 



now running upwards in the branch, now running downwards. Neither 

 the beginning nor the end of this burrow was found. The branch was 

 somewhat less than an inch in diameter. Another burrow was traced 

 upwarfls in a branch of about half an inch in diameter a distance of 

 aljout 18 inches, then doubling upon itself ran downwards parallel to 

 the upward course." I followed the burrow shown in Fig. 32, from the 

 ])oint where the grub had formed its hibernating and transforming cell 

 in tlic wood back to the starting point on a branch about an inch in diame- 

 ter and two feet long. The course of the l)urr()W is slitiwii in the figure. 

 1)nt one can get from the picture but a faint notion of the numerous 



