INSECT ENEMIES OF EASTERN FORESTS 3 
RELATION OF INSECTS TO FOREST AND 
ORNAMENTAL TREES 
Insects are among the most abundant forms of hfe in the forest. 
They exert a continuous influence through all stages of the growing 
and mature forest. For ee some attack the fruit or seed, often 
limiting reproduction of certain species; some injure or kill seedlings 
and young trees, thus exerting an important influence on the compo- 
sition of the young forest ; others frequently harvest, so to speak, the 
mature forest and set the stage for the development of a new stand; 
and some even play a large part with their allies, the fungi, in the 
decomposition of the dead frees that otherwise would litter the eround. 
The manner in which the entomological factors operate in any for- 
est is extremely complex, depending on such things as the proportion 
of certain species of trees in the forest at any given time, the relative 
abundance of the numerous species of insects, the presence and abund- 
ance of parasites and predators of the injurious insects, and weather 
conditions. In virgin timber stands, particularly those that are over- 
mature, a normal loss is going on steadily as the result of insect activity 
and other factors, but such loss for the most part is offset by growth. 
The wonderful forests that the white man found in this country were 
not static but continually dying and re-forming. Insects, disease, and 
fire are nature’s chief tools in removing the old and weakened trees 
in this process of renewal. 
On the Kaibab National Forest, Ariz., there are reliable records in 
the trees themselves, going back nearly 400 years, of repeated insect 
outbreaks. Large blocks of timber were killed by the Black Hills 
beetle, but these areas were later reseeded and restocked. In more 
recent times extensive areas of lodgepole pine in the northern Rocky 
Mountain region have been devastated by the mountain pine beetle ; 
and in those sections where the outbreak passed some 20 or 25 years 
ago, a new stand is forming from the remnants left by the beetles. 
Should fire sweep through the dead debris, it would destr oy everything 
and necessitate a new start from seed. The great majority of insect 
species are neutral or even beneficial in that ‘they play a role in the 
eradual disintegration of the dead and dying trees and help make 
way for new growth. 
There are no species of trees that are not fed on by some insects, 
although several kinds are relatively free from serious injury. 
Usually those species of trees that are most abundant or most prolific 
suffer the greatest losses. 
The question is frequently asked, “Where did these destructive 
forest insects come from?” Most of them have been here as long as 
the trees on which they feed. Most species of forest insects, both in- 
jurious and beneficial, are native to these forests and are usually dis- 
tributed throughout the range of their favorite host. Given favor- 
able conditions for their increase, their populations can suddenly build 
up from the few individuals normally present to epidemic numbers. 
On the other hand, a number of foreign pests have been introduced 
and have become established in the eastern part of the United States, 
where the food supply and climatic conditions are favorable for them. 
