INSECT ENEMIES OF WESTERN FORESTS 143 



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, page 161. 

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

 brown heads which usually leave many oblong im- 

 pressed excrement pellets termites, page 162. 



INSECTS WORKING IN UNSEASONED LOGS OR LUMBER 



THE AMBROSIA BEETLES OR PINHOLE BORERS 



Ambrosia beetles {S£) 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. Tlie beetles of this destructive group belong to the families 

 Scolytidae and Platypodidae, and although related to the bark 

 beetles, they have very distinctive habits. 



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

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

 logs, 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 different species. 

 Some construct an open, simple cavity; others a long, winding, cir- 

 cular gallery; while still others construct what is called a com- 

 pound tunnel in that small pockets or larval cradles are gnawed 

 along the main channel. Into the tunnels, either intentionally 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 at- 

 tack probably depends largely upon the requirements 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. The living require- 

 ments of these insects are very exacting. If moisture conditions 

 are not suitable the fungi fail to grow, and the beetles starve, or 

 if the fungi grow too abundantly, the beetles are unable to cope 

 with them and are smothered in their own food. For this reason 

 only moist, unseasoned wood is suitable for attack, and dried 

 seasoned lumber is immune. 



The shot holes and the accompanying stain are serious defects of 

 lumber and often render it worthless. In some seasons 30 percent 

 or more of the lumber from Douglas fir logs on the Pacific coast 

 has been ruined by the attacks of these beetles. Spruce airplane 

 stock has been badly damaged in this same region. Damage is 

 usually the greatest in the South or along the coast where mild 

 winters give favorable temperature and moisture conditions for a 

 long period of beetle activity. Where the winters are severe the 



