REPORT ON FORESTS. 217 



is held by a mere film of bark that will break in the first high 

 wind, carrying the borer to the ground in a shelter that remains 

 unchanged during the remainder of its larval and piipal life. 

 In the injured oak-shoots the larvae find ideal conditions for 

 their development, and they seem to realize that here there is 

 no necessity for girdling, because they make not the least attempt 

 in that direction. These borers remain in the trees one year 

 only, and after that the wood is no longer in the right condition 

 for them ; they leave it for others that delight in dead wood, and 

 of these there is no lack. There is another consequence, how- 

 ever : where so many beetles develop the}- are hard put to it to 

 find a place to breed, therefore they attack many trees that would, 

 under ordinary circumstances, escape. Hence apple trees are 

 frequently attacked and sometimes seriously injured, and large 

 shade trees in parks and gardens are subjected to a merciless 

 pruning. 



I think I have indicated sufficiently that the natural tendency 

 under normal forest condition is to eliminate the weakling and 

 the cripple, and that insects are among the chief agencies by 

 means of which this is accomplished. The hosts of species that 

 feed upon or in the foliage are comparatively of little importance 

 unless they strip the trees. This sometimes happens, and then 

 the proper conditions may be induced that result in a successful 

 borer attack. 



These borers are of three kinds, the bark or shot-hole borers, 

 Scolytids ; the flat and the round-headed borers, Buprestids and 

 Cerambycids respectively ; all of which have been already men- 

 tioned. 



The Scolytids are generally divisible into those that make gal- 

 leries under the bark and those that work in the solid wood. 

 The work of the former is most obvious, and their galleries, 

 radiating from a single central channel, are obvious when a flake 

 of bark is removed. Their method of causing injury is equally 

 obvious ; boring as they do between bark and wood, and partly 

 in each, they interrupt the flow of sap, and when many of them 

 are present, in effect, girdle the tree. These borers rarely attack 

 healthy trees ; but it does not need much to give them a foot- 

 hold. Trees in parks, without proper supply of nourishment or 

 in sod, on land too well drained, are often attacked and killed 



