INTRODUCTION Xlll 



method of warfare against injurious insects in the future. It should be 

 termed "the biological method of fighting insects" and, looking at the 

 problem in a broad way, so far as this country is concerned, when we 

 consider that more than one-half of our principal crop pests have been 

 accidentally imported from other countries, there seems no reason why a 

 systematic study of a very large number of parasitic and predatory 

 insects native to the countries from which these pests were accidentally 

 imported should not be made with a view of ultimate importation of 

 all of them into the United States. In fact, since there exist all over 

 the world beneficial insects, many of which can undoubtedly be accli- 

 matized here, and some of which will undoubtedly prove of value to 

 American agriculture, carefully planned work should be begun looking 

 to the ultimate increase of our insect population by the addition of as 

 many of these beneficial forms as possible. Of course this would mean 

 a very great amount of careful biological study in the countries of origin 

 by men specially trained in this sort of work, if results of value are to be 

 obtained. Strikingly beneficial results could not be expected speedily, 

 and, in fact, we might not be able for many years to estimate the bene- 

 fits derived from such a service; but it seems clear that we should have 

 in this country as many of these surely beneficial forms as can be 

 acclimatized." 



The greatest impetus to the development of economic entomology 

 was perhaps the establishment of Experiment Stations and Agricultural 

 Colleges where courses of instruction were given in this branch of 

 zoology, and where hundreds of students have been trained to undertake 

 investigations of the many insect problems that were awaiting solution. 

 An interesting feature of the latest development in the study of inju- 

 rious insects is the method of investigation that has been adopted in 

 most entomological stations. "Field stations" where the insects are 

 studied under both field and laboratory conditions are established in 

 infested areas, each in charge of an expert and a staff of assistants. 

 These officers also keep in close touch with the insect conditions of the 

 district, and are often able to "test out" control measures at many 

 places by interesting the farmers and orchardists in the valuable work 

 they are conducting. 



Even in a sketch of the main features of the rise of American eco- 

 nomic entomology, such as this is, mention must be made of some of 

 the pioneer entomologists who laid firmly and well the foundations of 



