INSECT INJURIES TO HARDWOOD FOREST TREES. 



315 



spines, which suggest its technical name. It appears on the wing from 

 Mav to August and hegin> its attack on the living trees at the base of 

 the luuls and leaves, apparently for the purpose of obtaining food; 

 later it enters the bark of the larger branches and top of the trunk and 

 excavates short longitudinal burrows (tig. 27, ,/) in the inner bark and 

 surface of the wood. The eggs, which are placed along the sides of this 

 primary gallery, hatch into small white grubs, or larva?, which burrow 

 at right angles through the inner bark and groove the surface of the 

 wood (fig. 27, It). The broods of larva* pass the winter in these brood gal- 

 leries, and the transforma- 

 tion to the adult takes place 

 in the spring in the outer 

 portion of the inner bark. 

 The adults emerge through 

 holes in the outer bark (fig. 

 2!) to continue their dep- 

 redations on the buds and 

 branches of other trees and 

 the remainder of the trunks 

 that were not killed by the 

 first attack. They com- 

 mence to emerge about 

 the middle of Ma}' in the 

 latitude of Morgan town, 

 W. Ya.. and two or three 

 weeks later in the latitude 

 of Detroit, Mich. Indi- 

 viduals of the hibernating 

 brood continue to emerge 

 until August, and may be 

 found excavating galleries 

 and depositing eggs as late 

 as September. Thus, they 

 will be found attacking 

 trees all through the sum- 

 mer, and all stages, from 

 very young to matured lar- 

 va 1 , will be found in the bark at the commencement of winter. In the 

 States north of Tennessee and North Carolina there is evidently but 

 one generation, while farther south there may be two. 



EXTERNAL CHARACTER OF THE IN.JTKY. 



The first indication of attack is shown by the leaves, some of which 

 die and remain on the twigs, while others fall earlv in the season. 

 Later, in July and August, the larger branches or the entire top may 



FIG. 27. Work of the hickory bark-beetle on surface of 

 wood beneath the bark: a, primary gallery; b, larval 

 mines. (Original.) 



