APPLE INSECTS — BOEERS AND MISCELLANEOUS 189 



bark and it often accumulates in little piles at the base of the 

 tree. It is generally believed that it requires three years for 

 this apiDle-borer to complete its life-cycle. During the third 

 summer the grub sinks its tunnel deeper into the wood, enlarges 

 it and finally extends it outward to the bark. Behind itself 

 the grub packs the tunnel full of sawdust and coarse, woody 

 fibers, and the outward end near the bark is also similarly 



Fig. 183. — Round-headed apple-tree borer pupa in its burrow 



plugged. On smooth-barked trees a small, slightly sunken area 

 of dead bark often marks the end of this tunnel, and thus 

 enables one to locate the borer from the outside before it trans- 

 forms -and emerges. A small chamber an inch or more in 

 length is left near the end of the tunnel where the grub hiber- 

 nates practically secure from the entrance of enemies in either 

 direction. Doubtless some of the grubs do not make this final 

 preparation for their further development into the adult insect 

 until the third spring. Early the third spring, often in May, 



