The Bronze Birch Borer. 



141 



The borer (Figs. 31 and 35) is a slender, 

 flattened, footless, creamy white grub about 

 three-fourths of an inch long when fully 

 grown. Its small head with dark brown mouth- 

 parts is retracted into the wide, flattened first 

 thoracic segment giving it a flat-headed ap- 

 pearance. The other segments of the body are 

 not so wide, the second and third thoracic 

 being the narrowest. The caudal end of the 

 body ends in two brown, horny, forceps-like 

 processes with bidentate inner margins. It is 

 this slender creature which is responsible for 

 the killing of the trees. It may be found in 

 autumn by cutting into the trees beneath the 

 rusty-colored spots described on page 140 as 

 occurring on the bark ( Fig. 30, fl ) . These grubs 

 make tortuous or zigzag burrows in the sap- 

 wood around and across the trunk and 

 branches of infested trees, as shown in Figs. 

 36, a and 32. 



Work of the Insect 



Fig. 31. — The Bronze 

 Birch Borer, a. female beetle; 

 b, first abdominal segtnents 

 of male from below; c, grub 

 or borer. All enlarged about 

 three and one-half times. 

 {From Bull. 18, U. S. Bu- 

 reau of Entomology) . 



This borer attacks white birches of all sizes 

 from nursery trees to stately monarchs more than a quarter of a century 

 old. All parts of the tree, from branches a quarter of an inch in diameter 

 to the main trunk, may be infested. The top branches are always first 



attacked and killed, 

 then the infestation 

 spreads into the 

 other branches and 

 trunk. 



The tiny borer, 

 hatching from an 

 egg laid by the adult 

 or beetle on the bark, 

 begins 



mine 

 through 



Fig. 32. — Tee burrow of a single borer as if zigzagged aroiuid 

 and through this 2-foot branch for a distance of^ovcr 5 feet. 

 Much reduced. 



a narrow 

 or burrow 

 the bark. 

 The burrow is ex- 

 tended in a tortuous 

 direction 

 the branch. 



or 



zigzag 



along 



getting wider as the 



borer grows, and running mostly in the sap-wood just beneath the bark. 



