Courtesy Pa. Bur. For., For. Pest 
Manage., Middletown 
Figure 119.—Galleries of the twolined chestnut borer, 
Agrilus bilineatus. 
larvae bore directly through the bark to the cambium area. There they excavate 
galleries between the bark and wood, with occasional side trips into the xylem to 
molt and then to spend the winter. The galleries wind back and forth, usually across 
the grain of the wood. Mature larvae construct oblong cells in the wood or thick 
bark in which they spend the winter and pupate in the spring. Larvae of all sizes and 
ages have been found in infested trees during the winter, but the only ones capable 
of developing to adults were those which became mature before winter set in and 
were later subjected to subfreezing temperatures. In the North, 2 years are required 
to complete the life cycle; in the South there 1s one generation per year. The biology 
of the bronze birch borer in New Brunswick has been reported (62). 
The bronze birch borer prefers weakened or injured trees (765). Damage may be 
extremely severe in stands of such trees. Weakened residual trees following log- 
ging, and individual shade and ornamental trees weakened by drought or other 
factors, are often seriously injured. Enormous volumes of birch suffering from 
dieback have been killed in the Northeastern States and Canada. 
278 
