February, ’23] graham & ruggles: economic entomology and forestry 51 
tinction of the host, so might an insect become numerically so abun¬ 
dant as to annihilate its food-plant. Before the latter contingency 
threatens, however, the background of entomophagous parasites comes 
to the fore and saves the day for the plants. 
Trees and other vegetation of slow growth, where the developmental 
cycle extends over a period of years, occupy a more insecure position 
than their annual or biennial relatives, and are unable to take the same 
advantage of any temporary reduction in the ranks of their insect enemies. 
Nevertheless here too, the quick response of parasites to an increased 
abundance of their phytophagous hosts ordinarily effects a readjust¬ 
ment in numerical abundance before an extensive depletion of food- 
plants takes place. Thus, in France Clement finds 450 insect enemies 
of the willows and Coulon 1,400 species affecting oaks, all so regulated 
by parasites that they do not crowd out one another, nor do they eliminate 
their food-plants during the twenty-odd years required for the individual 
oaks to attain sexual maturity. 
Excessive outbreaks of forest pests, however, do occur; witness the 
larch sawfly, spruce budworm and the Gipsy moth in their native habi¬ 
tats, resulting in a prolonged depletion of food-plants over wide areas. 
One of our lessons of early childhood attempted to teach us that 
“we cannot eat our cake and have it too.” This was necessarily im¬ 
pressed upon us by firm parental persuasion. A wider biological ap¬ 
plication of this adage must introduce the term “parasitic persuasion” 
to designate the Spartan method adopted by Nature to conserve the 
cake. 
President J. G. Sanders: We will now have a paper by Mr. A. G. 
Ruggles and S. A. Graham, entitled “The Obligation that Economic 
Entomology owes to Forestry.” 
THE OBLIGATION THAT ECONOMIC ENTOMOLOGY OWES 
TO FORESTRY 1 
By S. A. Graham and A. G. Ruggles, Division of Entomology , University Farm , 
St. Paul , Minn. 
Abstract 
Forest Entomology has been neglected as compared with insects affecting other crops, 
despite the enormous losses in our important forest areas. The entomologist has 
inclined to the belief that forest insects can not be controlled and the forester has 
Tublished with the approval of the Director as Paper No. 360 of the Journal 
Series of the Minnesota Agricultural Experiment Station. 
