182 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



Key to Diagnosis of Insect Injury to Wood 

 and Wood Products (Cont,) 



C. Insects attacking sawed lumber, seasoned wood, or wood products. 



1. Small wormholes in wood, tightly packed with a very fine 



powder, powder sometimes pushed out through holes in 

 wood. Usually working in very dry wood. 



a. Small, nearly round tunnels in various hardwoods 



Powder-post beetles, p. 203 



b. Irregularly shaped tunnels in softwoods and hard- 



woods (see A, 3). 



2. Large cavities, lightly filled with excrement pellets or frass, 



not tightly packed with boring dust. Insects working in 

 either dry or moist wood. 



a. Made by big black ants which leave only chewed wood 



fibers in cavities or push these out of the tunnels, 

 leaving the same quite clean Carpenter ants, p. 206 



b. Made by soft, antlike insects with white bodies and 



brown heads which usually leave many oblong im- 

 pressed excrement pellets. .' Termites, p. 208 



1 Also from causes other than insects. 



INSECTS WORKING IN UNSEASONED LOGS OR LUMBER 



AMBROSIA BEETLES 



Ambrosia beetles (82) are important enemies of forest products 

 because of their ability to riddle the sapwood and even the heart- 

 wood, of unseasoned logs or poles with small round pinholes or 

 shot holes. These holes become surrounded with a dark-brown or 

 black stain. The beetles of this destructive group belong to the 

 families Scolytidae and Platypodidae. Although related to the 

 bark beetles, they have very different habits. 



The adults are small, reddish-brown to nearly black, cylindrical 

 beetles that select for their attack dying or freshly felled trees, 

 sawlogs, green lumber, or other unseasoned or moist wood such as 

 stave bolts, or wine, beer, or vinegar casks. Small round tunnels 

 are bored directly into the sapwood or heartwood; and since the 

 beetles do not feed on the wood, the borings are cast out of the 

 tunnels and collect on the surface of the bark or wood as a fine 

 light-colored powder. The character of the tunnels varies with dif- 

 ferent species. Some construct an open, simple cavity; others a 

 long, winding, circular gallery; while still others construct what 

 is called a compound tunnel, with small pockets or larval cradles 

 gnawed along the main channel. Into the tunnels, either intention- 

 ally or not, the adults carry the spores of certain fungi. These 

 become detached, and, if moisture conditions are suitable, the 

 fungi begin to grow along the walls of the galleries. Each species 

 of beetle has its own specific ambrosial fungus, and the selection 

 of trees for attack probably depends largely upon the require- 

 ments of the fungi. Some beetles specialize on certain species of 

 trees, while others are more general in their attacks. As the fungi 

 grow they are fed upon by the beetles and the developing larvae. 



