Insects, Diseases, Parasites 



INSECTS IN THE FOREST: A SURVEY 



F. C. CRAIGHEAD, JOHN M. MILLER 



NATURE has always used insects 

 for her own purposes in forests. 

 Some insects are housekeepers. Some 

 are only incidental parts of the forest 

 environment. Some merely prune trees. 

 Others kill living trees, but even they 

 do not destroy the capacity of the forest 

 to restock and produce new stands of 

 trees. We have convincing evidence 

 that vast areas of mature timber were 

 demolished in the past by insect hordes, 

 only to regenerate after the epidemics 

 had run their course. This was nature's 

 way before man went into the woods. 

 Even primitive man could not have 

 been greatly worried by the insects that 

 killed the forests where he got shelter 

 and meat: Wood was plenty for all; 

 time was plenty for young trees to 

 grow up. 



But in modern civilization those 

 things have changed : Now the activity 

 of destructive insects upon the trees 

 and in the forests does matter; great 

 areas have been cleared of forest 

 growth for agriculture ; increasing pop- 



Above: Among enemies of forests are bark 

 beetles and dwarf mistletoe. 



ulations have increased the use of 

 wood. Now in his search for timber 

 stands to meet the need for sawlogs, 

 pulp, and box shocks, the lumberman 

 finds some areas where insects got there 

 first and harvested the pick of the crop. 

 For the forest resources and the com- 

 mercial and esthetic values involved, 

 we have joined battle, insects versus 

 man, and man, for all his science and 

 machines, is not yet the winner. 



A reason why that is so is to be found 

 in the nature of the insect infestations. 



Insect populations and the timber 

 losses they create fluctuate from year to 

 year; only sporadically do spectacular 

 outbreaks occur. The insects normally 

 are present in the forests in small num- 

 bers and only occasional trees are in- 

 jured or killed. A sort of natural bal- 

 ance seems to persist under which the 

 processes that permit forests to reach 

 maximum production go on uninter- 

 rupted. Then, all of a sudden, some- 

 thing happens to disturb this balance. 

 A destructive insect pest appears in 

 great numbers over wide areas and for 

 several years its ravages may continue 



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