EXCLUSION AND RESTRICTION 327 



are now in evidence showing the possibihty of controUing 

 injurious, introduced species by means of the introduction of 

 the native enemies. The most conspicuous is that of the 

 cottony cushion scale, introduced into Cahfornia 'several 

 years ago, and in more recent years the very extensive intro- 

 duction of predaceous and parasitic enemies of the Gipsy 

 and brown-tail moths in the New England States for the 

 control of these very destructive imported pests. 



EXCLUSION AND RESTRICTION. 



These are most important means of controlling insect 

 depredations. Formerly the entomologist devoted his 

 entire attention and effort to the study of native species 

 but now his attention is largely directed toward exclusion 

 from and restriction in the United States of new insects. 

 Until recently in the introduction of new plants from foreign 

 countries, no attention has been paid to the new insects 

 introduced with them. An important part of the work of 

 the entomologist in the future will be to study the insects 

 of other countries — not only those that are now destructive 

 there but those that do no particular damage, yet when 

 the natural checks are removed, are likely to become 

 destructive. 



Special attention must be paid to those insects which are 

 native in those countries from which we import a greater 

 part of our plants. Some of the foundation principles in the 

 study are : 



1. An insect, coming from another country, is more likely 

 to become destructive here if it comes from a somewhat 

 similar climate, and if the food plants are somewhat closely 

 related to those of its native country. 



2. Insects coming from different climates may, if they have 

 a wide range of food plants, adapt themselves to the new 

 climate. It will then be proper to consider tropical species, 

 especially if their food plants are widely distributed and 

 have nearly related species in the country to which they are 

 brought. 



