Insects in the Forest: A Survey 



409 



and snags, which are thus returned to 

 the soil. They compete with man, 

 however, when he decides to utilize 

 the tree, and attack the wood both 

 during the process of manufacture and 

 after it is in the finished product. 



Termites and wood borers in their 

 concealed ways work along method- 

 ically year after year. Their destruc- 

 tion never flares up in spectacular 

 peaks, but the annual attrition is none- 

 theless disturbing and serious. Pin- 

 hole and worm-hole borers attacking 

 green logs lower grades of lumber; 

 powder-post beetles in tool handles, 

 furniture, and flooring render quanti- 

 ties of finished material worthless ; the 

 old-house borer in the rafters of barns 

 and houses and termites in telephone 

 poles and foundations of buildings 

 claim an annual depreciation requir- 

 ing c'onsfant vigilance and replace- 

 ment of the damaged wood products. 



ESTIMATES OF THE MONETARY VAL- 

 UE of wood material and esthetic values 

 that are destroyed annually by forest 

 insects are subject to many reserva- 

 tions. The money value of the forest 

 products varies like that of other com- 

 modities, according to demand, avail- 

 ability, and the buying power of the 

 dollar; and the esthetic value of trees 

 that are killed in parks and recrea- 

 tional areas can seldom be expressed in 

 terms of money. Although some esti- 

 mates have been made which indi- 

 cate that Nation-wide timber losses 

 run into millions of dollars annually, 

 they are based on too many assump- 

 tions to be of value in this discussion. 

 However, if we consider only the actual 

 board feet or cubic volume of timber 

 that is killed by insects, we find that 

 this can be measured with consider- 

 able accuracy for specific areas and 

 periods. Forest-insect surveys have 

 been made to compute the volume of 

 timber destroyed in many areas that 

 have suffered from bark beetle and de- 

 foliator epidemics. Such surveys have 

 been made in the New England States, 

 where the spruce budworm destroyed 

 250 million cords of fir and spruce, and 



in the Western States, where bark 

 beetles killed 45 billion board feet of 

 pine in recent epidemics. 



All in all, these varied insect activi- 

 ties, involving tree seeds, the natural 

 restocking of the forests, the forest 

 plantations, second-growth and mature 

 stands of timber, green logs and lum- 

 ber/ telephone and telegraph poles, 

 cross ties and buildings, create a sub- 

 stantial loss that must more and more 

 be reckoned with and prevented as our 

 timber resources become smaller. This 

 loss is often compared with that from 

 forest fires even though all such com- 

 parisons are difficult and incomplete. 



PREVENTION is the starting point. 

 If he is sufficiently interested and acts 

 in time, man can save for his own use 

 much of the timber that insects will 

 otherwise destroy. There are two ways 

 of going about it. 



One approach is to initiate repres- 

 sive measures against the insect popula- 

 tions that are causing the losses. In the 

 case of bark beetles, the broods are 

 destroyed by peeling and burning the 

 infested bark or by applying a toxic 

 penetrative spray to the bark surface. 

 In the case of defoliators, that usually 

 involves spraying the trees with chemi- 

 cals which will either kill the insects on 

 contact or poison them through their 

 food. These repressive measures have 

 been termed direct control. 



The second approach is to prevent 

 the build-up of destructive insect popu- 

 lations by preventing conditions in the 

 forest that are favorable to their in- 

 crease. Healthy, rapid-growing stands 

 of timber are less susceptible to in- 

 festations of the defoliators and bark 

 beetles than are the slow-growing ma- 

 ture stands. Logging out the more sus- 

 ceptible tree species in a mixed forest, 

 selective logging in pure stands to take 

 out the most susceptible trees, thin- 

 nings to encourage more rapid growth, 

 and regulation of slash conditions to 

 remove favorable breeding ground for 

 the insect populations, all reduce the 

 chances that insect populations will 

 become destructive. These are meas- 



