October, ’23] 
FOREST ENTOMOLOGY IN UNITED STATES 
417 
sible areas of the country, control work against forest insects could never 
be undertaken. 
Artificial control embodying these principles has been carried on ex¬ 
tensively both in the east and in our western forests and has resulted in 
the saving of millions of feet of standing commercial timber from de¬ 
struction by insects. The control projects which have been instituted 
on these principles by the Forest Service, Park and Indian Services, 
state and private owners are too numerous to mention but the success 
of the methods has been well established. 
Removal of 50% to 75% of the infested timber brings about a re¬ 
duction in the loss of from 60% to 80% in the first year and, as has been 
recently demonstrated in Southern Oregon and Northern California on 
the largest project yet undertaken, at a cost which leaves a profit at 
the end of the first year’s work. 
On a project in Northeastern Oregon from 1910 to 1913, as a result 
of extensive and intensive investigations, Dr. Hopkins was able to 
prove that a case of long standing epidemic infestation of Dendroctonus 
monticolae Hopk. in inferior species of timber such as lodgepole pine will 
not migrate to any extent to another and more valuable host such as 
yellow pine, although the stands are adjacent and intermingled. This 
is extremely valuable data since control work in lodgepole pine, es¬ 
pecially in inaccessible areas, is often impractical. 
Contributions by Assistants of Dr. A. D. Hopkins 
Along the line of silvicultural control much important work has already 
been done. W. F. Fiske, a former assistant of Dr. Hopkins, in 1913, 
after a study of the favorable food plants of the gipsy moth, advocated 
pure stands of trees which were unfavorable to the gipsy moth larvae, 
or in association with less favored food plants. He also found that 
mixed stands of oak and white pine were only slightly less susceptible 
to serious damage than pure stands of oak which is the favorite food 
plant. This was the real beginning of silvicultural control work in this 
country, although it has long been known to foresters and forest ento¬ 
mologists that, in general, pure stands are more susceptible to their 
particular enemies than mixed stands. The main difficulties to be 
encountered in practices embodying pure stands or mixed stands are to 
be found in the fact that, while a pure stand of one forest tree will be 
practically immune to the insect for which one recommendation is made, 
it offers in its turn an exceptional opportunity for wholesale loss from 
another insect. Hence, it can be readily seen that studies over many 
years must be made before positive instructions regarding silvicultural 
