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 wihoni 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 

 Aving covers, and broad heads. They construct round, winding 

 tunnels, of a few inches to a foot in length (fig. YO), into the sap- 

 AYOod a n cl heartwood of 

 dying, weakened, injured, 

 or recently dead or felled 

 balsam firs, Douglas fir. 

 spruce, and hemlock, and 

 sometimes other conifers. 

 x4.t intervals along the 

 main tunnel secondary 

 tunnels branch horizon- 

 tally. Eggs are deposited 

 loosely in small clusters 

 in the tunnels, each female 

 laying 100 or more. The 

 young larvae w a n cl e r 

 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 cells 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 North w^est, 

 where it is the only repre- 

 sentative of the family 

 Platypodidae. 



The wood stainers of the genus Gnathotrichus are small, cylindri- 

 cal, 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 

 \¥estern States, and one species w^orks in alder. Their work is dis- 

 tinguishable from that of other w^estern 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 : 



Figure 71. — Damage to sapwood ot wesrern white 

 pine log caused by an ambrosia beetle {Trypoden- 

 dron sp.). 



130643° — 39- 



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