132 Control of Parasites 
indifferent to such efforts, and as long as a few breeding 
places are maintained by private indifference or lack of 
public spirit, all efforts can be only partially successful. 
Unless laws and ordinances compelling everybody to keep 
his premises free from these nuisances are passed and en- 
forced by fines and otherwise, we shall always have these 
pests with us. 
In Germany, such laws of general application and ordi- 
nances for given localities, especially for combating insect 
pests in forests, have been in vogue for a long time. It is 
only by constant vigilance and by the absolute enforcement 
of such laws that the Colorado potato-beetle, again and 
again imported, has been kept out of Prussia. 
Although in street and ornamental plantings the methods 
of combating insects are naturally different from those 
which are employed by the forester, the tree-warden can, 
nevertheless, be greatly benefited by knowing those of his 
brother arboriculturist in the forest. 
The forester, being chiefly concerned in economic prob- 
lems, considers first the question of economy and of rela- 
tive cost; he must balance the advantage in expenditure for 
combating an enemy with the saving in ultimate revenue 
resulting therefrom: he will, therefore, often let matters 
take care of themselves and suffer the damage, if he can sce 
that it is not too serious. The tree-warden, who has no 
economic object to attain, has no basis for calculating what 
he can afford to pay for the luxury of shade and beauty. 
Yet as he will want to avoid any unnecessary expense, he 
should follow the same line of reasoning as the forester in 
judging of the necessity and method of combating a pest, 
although he may come to a different decision. Especially 
in parks and large country estates the question of practi- 
cability may become serious. 
