DEFECTS IN TIMBER CAUSED BY INSECTS 43 



More general and excessive bluing by stain fungi in green lumber 

 after it has been sawn causes a sound defect and is also called " sap 

 stain." Rapid handling of the logs, kiln-drying the lumber, steam- 

 ing it in a kiln, and air-seasoning are preventive measures. Dipping 

 the lumber in chemical solutions is effective under certain conditions, 

 but this method of prevention has not been entirely satisfactory (37, 

 38,^0). 



DEFECTS CLASSED AS PITH FLECKS 

 PITH-FLECK INJITEY CAUSED BY THE LARVAE OF FLIES 



Birch, cherry, maple, oak, poplar, and many other less commonly 

 used hardwood trees have small " pith flecks," i. e., yellow-brown 

 spots or narrow streaks in the sapwood and heartwood, due to the 

 burrows made by larvae of flies 43 in the cambium of living trees 

 (fig. 45) (2, 21, 22). This is a very common and widespread defect, 

 more common in soft than in hard maples, and more common in 

 river birch (Betula nigra) than in the other birches. Where clear 

 birch is used, as for spool stock, it throws out considerable material. 

 However, this is merely a trade prejudice and should be overcome 

 by educational propaganda, in accordance with the move for closer 

 utilization. This is a sound defect caused in the living tree, the 

 flies laying their eggs in young branches and burrowing down the 

 trunk through the cambium long distances to the roots, where they 

 emerge and pupate. There is no known remedy to prevent the insect 

 injury to the living tree, and hence there is greater need for closer 

 utilization of the product. 



PITH-FLECK INJURY CAUSED BY THE FEEDING OF ADULT WEEVILS 



Another pith-fleck defect is that caused by the feeding of adult 

 weevils. 44 This defect has been described (If.8) as occurring in fir. 

 The adults puncture the bark to feed on the inner phloem, removing 

 a small circular or oval disk one-fourth inch in diameter to one- 

 fourth by 1 inch. This cavity fills with scar tissue and some gum 

 and later heals over. It is very common in fir, but is not of much 

 commercial importance. No doubt this defect occurs in other trees, 

 as pine and spruce, which are attacked by species of this genus of 

 weevils. 



SUMMARY 



Defects in timber caused by wood-boring beetles and grubs cause 

 serious losses either by rendering the affected material unfit for use 

 or by reducing it to lower grades. 



Much of this loss can be prevented through proper methods of 

 lumbering and management, usually involving but slight changes 

 or modifications in present handling of the timber. 



Some of the damage can not be avoided, but in such cases con- 

 siderable loss can be prevented by periodical inspection and proper 

 classification, piling, and handling of stock. More rapid and closer 

 utilization of the material can often be attained. 



i3 Agromyza spp. ** Pissodes dubius Rand. 



