CIVILIZATION AND INSECTS — SMITH 259 



{Lipoptenu depressa) and the head maggot {Cephenemyia sp.) of 

 deer may be cited as examples. 



SOME SPECIES OF INSECTS HAVE INCREASED IN NUMBERS 



It is easier to cite examples of forms which have increased as a 

 consequence of the activities of civilization. In the days of the old 

 prairie, many species of insects subsisted on the perennial grasses, but 

 the food supply was not abundant enough to permit the great increase 

 of any one species."* Under farming conditions there is no longer a 

 great number of species generally intermixed, but a few species 

 present, sometimes in very large numbers, in the almost pure stand of 

 some crop. A very large group of insects has adopted as food plants 

 these new crops which have partly replaced the primitive flora. 

 When the potato was brought to North America and was carried to 

 the home of the Colorado potato beetle, there was provided a real 

 opportunity for expansion for these insects. The potato, being a 

 member of the same plant genus as the beetle's native food plant, 

 the buffalo bur, was promptly accepted, and between 1824 and 1893 

 the beetle had attacked the introduced potato plant from the Gulf 

 States to Canada. This potato beetle has accepted the eggplant and, 

 less commonly, the tomato, peppers, and tobacco for food plants 

 also, all of which belong to the nightshade family. 



The chinch bug, a native feeder on some wild grasses of the great 

 plains, did not become plentiful until acres of corn, oats, wheat, and 

 grain sorghums were provided by modern agriculture. The corn 

 ear worm must have had a discouraging time, if one can judge by 

 present field conditions, before corn, cotton, tomatoes, and the rest of 

 its adopted food plants were made available by civilization. 



The Hessian fly bred on some ancestor of modern wheat, or on 

 other wild grasses, including wild rye, before civilization provided 

 acres of wheat for it to feed upon. In North America, it has never 

 been abundant except on wheat, barley, and rye, but it is known to 

 I'un its life cycle in small numbers interchangeably with certain wild 

 grasses, particularly of the genera Agropyron and Elyirms? While 

 in its native European home the Hessian fly had only one or two 

 generations a year, in the central part of the United States it could 

 generally have three generations a year, and sometimes in southern 

 Nebraska, most of Kansas, and northern Oklahoma, it could have 

 four or five generations. This indicates how much more favorable 

 the climate and food conditions are in its adopted country. 



*Metcalf, C. L., and Flint, W. r. Fundamentals of insect life, pp. 412-416. New 

 York, McGraw-Hill, 1932. 



"Noble, W. B. Two wild grasses as hosts of the Hessian fly. Journ. Agr. Res, vol. 

 42, no. 9, pp. 589-592, 1931. 

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