INSECT INJURIES TO FOREST PRODUCTS. 391 



eggs are deposited in the young pods, so that the entrance burrows 

 made by the minute young larvrc are completely hidden before the 

 nuts are matured. After the larvae in nuts complete their growth 

 they bore their way out and enter the ground to pass the winter, and 

 transform to the adult the next season. In certain kinds of seeds the 

 transformation to the adult takes place within. a 



DRUG 1JRETLE8. 



Injury by this class of enemies to certain medicinal products of the 

 forest consists of the honeycombed, sieve-like, or powdered condition 

 of certain kinds of barks, roots, stems, leaves, and seeds. The insects 

 responsible for the work belong to the class of true powder post borers, 

 and have similar habits. 



CONDITIONS FAVORABLE FOR INSECT INJURY. 



CRUDE PRODUCTS. 



ROUND TIMBER WITH BARK ON-. Newly felled trees, sawlogs, tele^ 

 graph poles, posts, and like material, cut in the fall and winter and 

 left on the ground or in close piles during a few weeks or months in 

 the spring and summer, are especial^ liable to injury by ambrosia 

 beetles (figs. 43, 44, and 45), round and flat-headed borers (fig. 46), 

 and timber worms (fig. 47), as are also trees felled in the warm 

 season and left for a time before working up into lumber. The proper 

 degree of moisture found in freshly cut living or dying wood, and the 

 period when the insects are flying, are the conditions most favorable 

 for attack. This period of danger varies with the time of the year the 

 timber is felled and with different kinds of trees. Those felled in late 

 fall and winter will generally remain attractive to ambrosia beetles 

 and the adults of round and flat-headed borers during March, April, 

 and May. Those felled in April to September may be attacked in a 

 few days after they are felled, and the period of danger may not 

 extend over more than a few weeks. Certain kinds of trees felled 

 during certain months and seasons are never attacked, because the 

 danger period prevails only when the insects are flying; on the other 

 , hand, if the same kinds of trees are felled at a different time, the con- 

 i ditions maj T be most attractive when the insects are active, and they 

 will be thickly infested and ruined. 



The presence of bark is absolutely necessary for infestation by most 

 | of the wood-boring grubs, since the eggs and young stages must 

 ; occupy the outer and inner portions before they can enter the wood. 

 Some ambrosia beetles and timber worms will, however, attack barked 

 logs, especially those in close piles and otherwise shaded and pro- 

 tected from rapid drying. The sapwood of pine, spruce, fir, cedar, 



For further information on these insects, see article by F. H. Chittenden, Bulle- 

 tin No. 44, Bureau of Entomology, pp. 24-43. 



