INSECT ENEMIES OF WESTERN FORESTS 183 



The living requirements 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, or pin holes, and accompanying stain are serious 

 defects of high-grade lumber. In certain seasons ambrosia beetles 

 on some Pacific coast logging operations have degraded 30 percent 

 or more of the sapwood of Douglas-fir, Sitka spruce, and western 

 hemlock, rendering it valueless for such uses as rayon pulp, air- 

 plane stock, and finishing lumber. Damage is usually greatest 

 where mild winters give favorable temperature and moisture con- 

 ditions for a long period of beetle activity. Where the winters are 

 severe the beetles become inactive and thus a longer period may 

 elapse between the time of cutting and the removal of logs, before 

 damage becomes important. 



The control of ambrosia beetles is largely a matter of preven- 

 tion of damage through the regulation of woods practice and 

 proper handling of the products from the mill. Logs cut in the 

 summer or fall should be removed from the woods within a week 

 or two after cutting and either placed in water or run through 

 the mill (109) . Logs cut late in the fall, in midwinter, or early in 

 the spring will be reasonably safe until the approach of warm 

 weather but often cannot be removed before damage has occurred. 

 Freshly sawed lumber will be safe from attack if it is dried 

 quickly, but some damage may occur in storage if the lumber is 

 piled so as to remain or become moist. Logs or wood either heavily 

 soaked with water or quite dry are not suitable for attack, but 

 the exposed parts of logs left floating in ponds are very likely to 

 become infested. In general, the control of these beetles is very 

 difficult, and prompt utilization or kiln drying of the lumber is 

 about the only satisfactory solution (79). A small amount of para- 

 sitism has been noted in studies connected with the work of these 

 beetles in seasoned products, 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 wilsoni Sw.) is 

 very different from the other species in that the adults are long, 

 slender, somewhat flattened, reddish-brown, shining beetles about 

 % 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. 83,A), into the sapwood 

 and heartwood of dying, weakened, injured, or recently dead or 

 felled true firs, Douglas-fir, spruce, and hemlock, and sometimes 

 other conifers. At intervals along the main tunnel secondary tun- 

 nels branch horizontally. Eggs are deposited loosely in small clus- 



