In spite of these expenditures, however, the number of species of our insect foes is on the increase. One cause of this is the change of conditions due to cultivation of crops. Con spicuous among the innocuous insects that have developed destructive habits is the Colorado potato beetle which in its native condition fed upon nettles and other plants of no consequence to man, but transferred itsapetite to the Irish potato and the egg plant when these were introduced into its original habitat. Though now the principal insect enemy of these crops and though largely held in check by systematic spraying with poisons, it still costs the country millions of dollars in reduced and in expenditures for materials, machines and labor to keep it in check.
A more important factor than change of habit in the increase of our insect foes lies in commercial intercourse with foreign countries, more especially those of Europe, whose insect pests are thus accidentally imported or ex ported. Herrick is authority for the state ment that out of 73 of our worst insect pests 37 or more than half have been imported from foreign countries. Conspicuous among these are San Jose scale from Australia, cotton boll weevil from Mexico, gypsy moth, eurrant worm, wheat midge, clover midge and Hessian fly and many others from Europe. In similar manner, but to a much smaller extent, America has disseminated insects in foreign countries. Most conspicuous among these is probably the phylloxera or root louse, which for over 200 years, as discussed in 'Evolution of Our Native Fruits' by Bailey, was a leading agent in preventing the successful commercial culti vation of European grapes in the eastern half of the United States and thus indirectly led to the development of our native species of grapes, and which when accidentally exported to Europe wrought havoc among the established vineyards, particularly of France, and thus led to the practice of grafting Eilropean varieties on American stocks, thereby not only saving the French wine industry, but also making it possible to grow European varieties on a com mercial scale in the United States and perhaps in Canada. Such cases as these being possible of repetition at any time have led to the estab lishment of national and State regulations with respect to interstate and international trans portation of nursery stock and the employment of trained men to examine such stock where grown and at ports of entry. Not only have the United States and Canada passed such laws and appointed inspectors, but many other coun tries are now similarly provided.
Because insects in all these enumerated ways and many others profoundly affect human interests, especially those which relate to agriculture, to manufactured organic materials, to health and to the products of such species as bees and scale insects, it is but natural that the new branch of economic entomology should have been developed as probably the most important division of biology, certainly of the animal side of this great subject. In no
country of the world has the necessity for such development been so great as in America, es pecially in the United States. This is not only because of the enormous area of this nation, the great variety of products grown, nor the differences of climate, nor even a combination of all these factors, but also largely because the country is comparatively new, because the insect pests introduced from other countries have generally been brought in without the natural enemies that kept them more or less under control where they were indigenous, and finally because mady of our native species have left their original food and developed tastes for the new plants, animals or the products of such brought within tempting reach of them. While economic entomology had its inception in Europe, necessity and American progressiveness and inventiveness have so fostered and en couraged it on this side of the Atlantic that the United States not only leads the world in its insect investigations and successful methods of control, but it employs a larger force of official economic entomologists than do all other countries of the world put together.
Still further, economic is one of the leading subjects in the curriculum of all leading agricultural colleges and schools be cause it is required that all teachers and in vestigators of agriculture, all farm bureau or county agents, all agricultural extension specialists, and all inspectors of nursery stock, must have as thorough a grounding in this subject as in botany, and physics in order to hold staff positions in the National Department of Agriculture, those of the respec tive States, or in the colleges and schools which teach agriculture from the practical standpoint. Herein lies another item of expenditure that ag gregates millions of dollars annually and thereby increases the enormous figures pre sented. But all this expenditure and study is necessary and justified because it is essential to man's well being that these foes shall be destroyed in order that man may have his right ful dominion over the earth and its creatures.
For methods of controlling insects (see IN SECTICIDE) under which title will also be found a list of important books and other writings which deal with the control of these creatures by natural and artificial means.
M. G. !Canis, Horticultural Consultant.