INSECT ENEMIES 

 OF WESTERN FORESTS 



By F. P. Keen, entomologist, Division of Forest Insect Investigations, Bureau 

 of Entomology and Plant Quarantine, Agricultural Research Administration 



The protection of forests from destruction is the first require- 

 ment in the practice of forestry. Insect pests rank high among 

 the important destructive agents. Although the damage they cause 

 is less spectacular than that done by fire or wind, it may result 

 in great losses of timber. Insects are constantly at work in the 

 forest and cause a steady drain on timber supplies. To allow them 

 to run unchecked through our forests is to invite disaster and 

 threaten present and future supplies of timber. 



Injurious insects may be encountered in every forest operation, 

 from the collection of seed through the planting, growing, and 

 harvesting of the trees, in the handling and protection of wood 

 products, and even in the management of grazing lands. It is 

 hoped that the information assembled in this handbook will aid 

 timber owners and foresters in recognizing the work of important 

 western forest insects, in applying suitable control measures, or in 

 adjusting forest practices so as to reduce losses from this source 

 to the lowest possible point. 



KINDS OF FOREST INSECTS AND 

 THE LOSSES THEY CAUSE 



All forests are swarming with insect life. This insect population 

 serves many functions and is as much an essential part of the 

 complex association of living, growing, and dying organisms which 

 we call the forest as are the trees themselves. 



Of the thousands of insect species found within our forests, 

 many are harmless, or even beneficial. A great many feed on dead 

 trees and on fallen limbs and other debris upon the forest floor, 

 and thus hasten the disintegration of dead material and make 

 room for new growth. Many others prey upon destructive insects 

 and hold them in check. 



A certain proportion of the insect species, however, are dis- 

 tinctly harmful, as they attack healthy or partially weakened trees 

 and impair their vitality or even kill them. Of this group, bark 

 beetles destroy more standing timber in our western forests than 

 all other insects combined. Defoliators — insects that feed directly 

 on the foliage — are the next greatest destroyers of standing tim- 

 ber. Other insects, such as weevils, tip moths, pitch moths, and 

 cone beetles, attack various portions of the green trees, often with 

 serious results. In spite of the large number of insect species that 

 prey upon the forests, comparatively few cause damage of eco- 

 nomic importance. 



Injurious insects may be roughly classed as primary or sec- 

 ondary, depending on the health of the trees they normally attack. 



