EEPFECT. OF PHYSIGAL FACTORS ING DHE COEOGX= Oe 
CERTAIN INSECES IN=LOGS* 
By S. A. GRAHAM 
The study of forest entomology, like that of almost every branch 
of the biological sciences, was first based upon purely empirical knowl- 
edge of the insects concerned. The forester learned by experience 
and superficial experimentation how the pests of trees lived and repro- 
duced, and how they could be controlled. 
In Europe, where labor was cheap, there were developed many 
mechanical methods of forest insect control such as trapping and other 
devices for collecting injurious species, poisoning, and banding. In 
America such means as these have proved too expensive and difficult 
of application for general use, since the margin of profit in growing 
trees for market is small and requires that the expense of all the 
operations involved in producing a crop of timber be reduced to the 
minimum. 
For this reason we must turn our attention to the development 
of natural methods, where the elements of the environment are so 
balanced as to reduce the probability of extensive outbreaks of injurious 
pests. The working out of natural control methods is much more 
difficult than the more obvious artificial methods, but it has the decided 
advantage of reducing the danger of insect loss to a minimum without 
materially increasing the cost of producing timber. The insect control 
plan will, under this system, be included in the silvicultural procedure 
set forth in the working plan. 
When we come to formulate satisfactory methods for the silvi- 
cultural control of forest insects, we soon find that empirical knowledge, 
superficial experimentation, and general observation do not form an 
adequate foundation upon which to build. We can not construct a 
substantial superstructure upon a foundation not based upon the funda- 
mental laws which govern insects activities. We must not only know 
the life cycle of the insects, as it is ordinarily determined by cage 
experiments, but we must also know how they react to the varying 
conditions of their environment and how they are affected by the 
other living organisms with which they come in contact. Thus the 
* This paper is a summary of a thesis presented in partial fulfilment’ of the requirements 
for the Degree of Doctor of Philosophy, University of Minnesota. The original thesis is 
filed in the Library of the University. 
Published with the approval of the Director as Paper No. 389 of the Journal Series of 
the Minnesota Agricultural Experiment Station. 
