INSECT ENEMIES OF WESTERN FORESTS 148 
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. 
b. 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 (52) 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, 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 orow 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 
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