34 SOME INSECTS INJURIOUS TO FORESTS. 



branches, and foliage of the locust, and during their principal period 

 of activity, from toward the last of August to the middle of Septem- 

 ber, they are especially common on the golden-rod flowers. Mr. 

 Fiske determined that they were also actively copulating and deposit- 

 ing eggs as late as 10 o'clock at night. 



The attack of this insect is apparently confined to the black or yellow 

 locust (Robinia pseudacacia). 



ECONOMIC FEATURES. 

 DESTRUCTIVE CHARACTER OF THE WORK. 



The destructive character of the work of the locust borer is a matter 

 of great economic importance. This insect attacks the otherwise 

 perfectly healthy trees, and in addition to causing the detrimental 

 wormhole defects in the wood it often kills the trees or renders an 

 otherwise valuable product worthless except for fuel. It is much 

 more destructive in some localities and sections than in others, and 

 also much more destruetwe to some trees in the same grove than it is 

 to others. It is more destructive also to young saplings and the 

 branches of medium-sized trees than to the larger trees. 



The death of a tree is caused principally by injuries to the inner 

 bark and cambium, resulting from repeated attacks. Injuries to the 

 wood alone do not result in the death of trees except when all of the 

 wood is practically destroyed or sufficiently injured to cause the tree 

 to fall or be broken down by the wind. 



The commercial value of the wood product is diminished or destined 

 by the wormhole defects, but for certain purposes, as, for instance, 

 fence posts, a limited number of such defects are not detrimental, 

 except so far as they ma} 7 contribute to decay. 



EVIDENCES OF ATTACK. 



The first evidence of attack is fine brownish boring dust and wet 

 spots on the bark, first observed in April, when the overwintered 

 larva? begin to enter the inner bark. As soon as the larvae begin to 

 groove the surface of the wood and enter the sapwood, their presence, 

 in addition to the wet spots, is indicated by yellowish boring dust 

 mixed with liquids and the gum-like exudations. After all of the 

 larvae have entered the wood their presence is plainly shown by 

 the quantities of yellowish boring dust lodged in the loose bark on the 

 trunk, in the forks of the tree or branches, and around the base. At this 

 stage, usually about the middle of May, the badly infested trees which 

 will die are plainly indicated by the failure of the leaf buds to open, 

 or by the dwarfed or faded and sickly appearance of the foliage, and 

 toward the last of the month and until the larvae have completed their 

 work in July, by the breaking down of the branches and small trees. 



