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BULLETIN 234 



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. Kept. 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 ; now 

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

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



FlG. 33. Portion of trunk of infested white birch, showing no injury apparent until the 

 tark is removed and the numerous burrows of the borer revealed. Natural size. 



less than an inch in diameter. Another burrow was traced upwards in a 

 branch of about half an inch in diameter a distance of about 18 inches, then 

 doubling upon itself ran downwards parallel to the upward course ". I 

 followed the burrow shown in Fig. 32, from (he point where the grub had 

 formed its hibernating and transforming cell in the wood back to the starting 

 point on a branch about an inch in diameter and two feet long. The course 

 of the burrow is shown in the figure, but one can get from the picture but a 

 faint notion of the numerous turnings and zigzriggings of the burrow as it 

 extended along and around the branch. Eight times the borer tunneled its 

 way through the wood to the centre of the branch or farther, once working 

 along for about four inches near the centre-. This burrow, the work of a single 

 borer, measured a little over five feet in length, and it was evidently all made 

 between June ist and Oct. ist. Surely this is a remarkable piece of work 



