]^32 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 



trance chamber. In the smaller limbs the galleries extend obliquely 

 around the limbs and may completely encircle them. They are 

 frequently very abundant in ash corclwood. 



The oak bark beetles {Pseudopityophthorus spp.) in some instances 

 attack so heavily as to cause the death of weakened oak trees. 

 Usually, however, these beetles confine themselves to injured, felled, 

 or recently killed trees or to the dead branches and twigs of other- 

 wise healthy trees. The adults are tiny, cylindrical, brown bark 

 beetles. Their typical work consists of transverse ^gg galleries ex- 

 tending for a short distance on either side of the central entrance 

 tunnel and diverging larval mines running longitudinally with the 

 trunk or limb. 



The mountain mahogany bark beetle {Renocis heterodoxus Csy.) 

 is a small brown bark beetle that mines the limbs and trunks of 

 mountain mahogany in Oregon. Nevada, and California. 



The shrub bark beetle {Micracis hirteUus Lee.) is a secondary 

 species which mines the hard, dry wood of many flowering shrubs 

 and broadleaved trees including willow, alder, and laurel in Cali- 

 fornia. The adults are dark reddish brown and about one-eighth 

 inch long. They have been found boring into lead telephone cables. 



The birch bark beetle (BrijocoeteH hetulae Hopk.) is a secondary 

 enemy of birch throughout British Columbia, Canada, and the 

 northern part of the United States. 



FLATHEADED BORERS 



(Buprestidae) 



The flatheaded or metallic wood borers {12) comprise a large 

 family of beetles the larvae of which mine in the inner bark and 

 wood of many species of forest trees. Their activities are diversified. 

 A few species attack and kill healthy trees by mining under the bark; 

 others bore into the inner bark and sapwood of trunks, branches, and 

 twigs of weakened and dying trees ; while others breed only in dead 

 or recently felled trees and make flattened, winding wormholes 

 through the wood. A few species are leaf miners. In general, the 

 group is a destructive one in that they sometimes kill living trees 

 and often reduce the value of lumber by their attacks. Others assist 

 materially in the natural process of disintegrating deadwoocl in the 

 forest, and these are decidedly beneficial. 



The adults are flattened, frequently brightly colored beetles with 

 a metallic luster. They fly and mate and then lay their eggs in bark 

 crevices or on the outer surface of the bark, early in the spring or in 

 summer. \Ylien the eggs hatch the young grubs construct long, 

 winding, oval mines in either the bark or the wood, or in both (fig. 

 65). These mines gradually widen as the grubs increase in size 

 and end in elongatecl, oval pupal cells. The slender white grubs are 

 the stage usually found in trees, and they can be recognized by their 

 long, legless bodies, shaped like a horseshoe nail. The head is small, 

 and the first segment back of the head is much broader than the fol- 

 lowing body segments and has horny plates on the top and bottom. 

 Growth of the larvae continues until fall, when activity ceases with 

 the advent of cold weather. The winter usually is passed in the 

 larval stage, although some larvae may pupate in the fall and pass 



