INSECT ENEMIES OF WESTERN FORESTS 145 
in studies connected with the work of these beetles in seasoned prod- 
ucts, but it is of insufficient importance to reduce appreciably the 
number of beetles and the injury they cause. 
Wilson’s wide-headed ambrosia beetle (Platypus wilsonit Sw.) is 
very different from the other species in that the adults are long, 
slender, somewhat flattened, reddish-brown, shining beetles about 
one-fourth inch in length, with a few long yellow hairs, projecting 
wing covers, and broad heads. They construct round, winding 
tunnels, of a few inches to a foot in length (fig. 70), into the sap- 
wood and heartwood of 
dying, weakened, injured, 
or recently dead or felled 
balsam firs, Douglas fir, 
spruce, and hemlock, and 
sometimes other conifers. 
At intervals along the 
main tunnel secondary 
tunnels branch horizon- 
tally. Kggs are deposited 
loosely in small clusters 
in the tunnels, each female 
laying 100 or more. The 
young larvae wander 
freely about in the mines, 
feeding on the ambrosial 
fungus, and reach matur- 
ity In 5 or 6 weeks. When 
full grown they excavate 
cells at right angles to the 
main gallery in which to 
transform to pupae and 
adults. These eells are 
parallel to the grain of 
the wood and are often 
arranged in groups of 8 
to 10 or more. The insect 
is distributed over the en- 
tire Pacific Northwest, 
where it is the only repre- = Ficure 71.—Damage to sapwood of western white 
sentative o f the family pine. Riya by an ambrosia beetle (Trypoden- 
. Platypodidae. 
The wood stainers of the genus Gnathotrichus are small, cylindri- 
eal, dark-brown or black beetles of the size and appearance of a short 
piece of pencil lead. They attack nearly all species of conifers in the 
Western States, and one species works in alder. Their work is dis- 
tinguishable from that of other western ambrosia beetles in that a 
primary tunnel penetrates the sapwood, and at intervals along this 
tunnel secondary tunnels branch horizontally, the branches more or 
less following the annual rings. The tunnels are of the compound 
type, in that larval cradles are constructed at regular intervals, both 
above and below the primary and secondary galleries. ‘The species 
so far recorded in the West are as follows: 
136650°—38——10 
, les 
Fie - ——- ia 
Qn 7 & + |» sR 38 
4) at 
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