OUR FORESTS 23 



from the attacks of insects than are broadleaf trees. This is espe- 

 cially true of some of the pines of the West and South which have 

 been greatly damaged by bark beetles. The western pine beetle is 

 to be found in the ponderosa pine forests of the Rocky Mountain 

 and Pacific Coast States. It generally attacks the trees in swarms 

 and burrows into the living bark. The female insects excavate gal- 

 leries in the inner layer of bark and deposit their eggs. After the 

 eggs hatch, the larvae in turn bore their way through the bark until 

 they have completed their growth. Their galleries serve to cut off the 

 natural movement of the sap and kill the treees by completely 

 girdling them. The larvae then bore into the outer corky bark, 

 where they make little cells in which to transform, first to the pupa 

 and later to the adult stage. The adults work their way out through 

 the bark and fly in swarms to living trees, there to continue their 

 depredations. The southern pine beetle, closely related to the western 

 pine beetle, works in much the same way. It attacks and kills 

 healthy pines of all species occurring within its range, which in- 

 cludes the Southeastern and Gulf States. 



Another extremely bad example of insect attack is that of the 

 gipsy moth, which many years ago became established in New Eng- 

 land. It attacks the oaks and several other broadleaf trees and 

 destroys mixed woodlands if not checked. The introduction into the 

 infested area of the Calosoma beetle and other insect enemies of the 

 gipsy moth has done much to lessen the ravages of this insect. 



FUNGOUS DISEASES 



Fungi attack the forest in many ways. Some kill the roots of 

 the trees; some grow upward from the ground into the trees and 

 change the sound wood of the trunks to a useless rotten mass. The 

 chestnut bark disease, or chestnut blight has ravaged the native 

 chestnut in this country. It is a parasitic fungus, introduced from 

 Asia on small nursery stock before this country had enacted plant 

 quarantine laws. Its minute spores float through the ail and spread 

 the disease. The spores find lodgment in the bark and the fungus 

 gradually grows down through it, eventually causing the death of 

 the tree. As yet no practicable means of controlling the chestnut 

 bark disease has been found but there is evidence that sprouts and 

 other young chestnuts are developing resistance to the disease. 



Another fungous disease is the white pine blister rust which, 

 strange as it may seem, lives alternately on the pine and on currant 

 and gooseberry plants. The disease enters the white pines through 

 the needles and grows into the bark. Diseased areas in the bark 

 are called cankers. About 3 years after a tree becomes infected 

 orange-yellow blisters break from the cankers. In the spring mil- 

 lions of spores from these blisters are scattered by the wind over 

 long distances, infecting the leaves of currant and gooseberry 

 bushes. The disease cannot go directly from one pine to another, 

 but must first go to currants or gooseberries. It is the spores 

 produced on the leaves of these plants that are dangerous to the 

 pine trees. Since these spores are delicate and short lived their 

 infecting range is limited to relatively short distances. Thus it is 

 possible to control the disease locally by destroying currants and 

 gooseberries in the vicinity of white pines. 



