416 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
ing aside appropriations by the states, $30,000 per year has been the 
average annual appropriation for the Division of Forest Insects of the 
Federal Bureau of Entomology and this, despite the fact that forest 
insects undoubtedly kill more merchantable timber in coniferous forests 
than does fire, for the control of which there are large annual appropri¬ 
ations by federal, state and private timber owners. 
Despite this shortage of funds, Dr. Hopkins and his assistants have 
given due attention to those phases of the subject which have been 
deemed most important, such as tree-killing barkbeetles and insects in¬ 
jurious to forest products, where there was most need and demand by 
owners for control methods. 
In addition, very complete biological investigations of the principal 
forest insects of the United States have been made by forest entomolo¬ 
gists of the federal and state governments and effective methods of con¬ 
trol have been determined for many of the most injurious species. 
Foremost, among the many notable contributions made by Dr. 
Hopkins to the science of forest entomology are the following broad 
principles regarding the work of combating forest insects in America: 
Economic Principles of Forest Entomology 
First, artificial methods of controlling destructive barkbeetles which include, (a) 
the percentage principle of control by which it is only necessary that enough of the 
depredating insects be destroyed to turn the balance in favor of their natural enemies; 
and (b) the host selection principle by which it is possible to control an insect attack¬ 
ing a valuable host tree without reference to those in a less valuable host, due to the 
adaptation of the insect to the host upon which it has fed for many years and the 
subsequent confinement of its attack to that host. 
Second, silvicultural control and business management , which will provide for the 
care of standing timber and the handling of crude and finished products in such a 
manner as to bring about unfavorable conditions for attack by the more destructive 
insects. This includes the use of pure stands to prevent the attacks of certain de¬ 
foliators and mixed stands in other cases; the removal of slash only where logging 
operations are sporadic or of short duration; and in the case of timber products the 
utilization of natural elements such as solar heat and water. 
Third, the Bioclimatic Law as a guide to (a) the proper dates and periods to apply 
a remedy in any given locality, (b) determine the natural distribution of an insect 
and (c) the sections of a state or country where artificial distribution from another 
country or an infested section in this country would be most dangerous as related to 
a destructive insect or most useful as related to a beneficial one. 
These principles which embody in part silvicultural and forest man¬ 
agement practices are being tried out on a large scale and if, after sufficient 
test, they prove true, they are the most important and economical 
principles ever advocated. Without such principles in certain inacces- 
