CIVILIZATION AND INSECTS SMITH 263 



plant. A similar trend is shown in the shift of grass insects to corn 

 and to the many kinds of feterita and sorghums. The papaya, avo- 

 cado, date palm, and similar lately commercialized fruits in the 

 United States, not yet severely attacked, may be expected to serve as 

 hosts to some serious insect pests before many years. 



The introduction of new crops into North America is likely to 

 continue indefinitely. These new crops probably will be free of 

 severe insect damage at first, but soon pests, by transfer or importa- 

 tion, will harass them. This has been the course of events in the 

 past. It will be interesting to observe the building up of the list of 

 pests of such new crops as the tung-oil tree in Florida, and the pine- 

 apple in the West Indies, lespedeza and the Chinese elm in the 

 Great Plains. 



INFLUENCE OF MODERN TRANSPORTATION 



In the last century, civilization has become increasingly in a hurry 

 to go places. Consequently, means of transportation have become 

 more varied and speedy. The excellent transportation facilities 

 provided since the first railroad in 1829 have been a great aid to 

 insects in extending their domain. Gypsy and brown-tail moth 

 larvae have been noted to drop on automobiles and be whisked off to 

 new feeding grounds. Egg masses of the gypsy moth were shipped 

 to Cleveland from New England on stone intended for building con- 

 struction. Quarantine officers during the summer stop automobiles 

 in certain sections in search of European corn borer stowaways on 

 green corn. The possibility of importing, in airplanes, infected 

 yellow fever or malarial mosquitoes from Central American coun- 

 tries to the shores of the United States has received consideration. 

 Likewise, the danger of spreading the West Indian, Mexican, and 

 the Mediterranean fruit flies in fruits carried by passengers who 

 may discard them, innocent of possible consequences, has been pointed 

 out repeatedly. So by railroad, steamboat, automobile, airplane, zep- 

 pelin, and all other transportation devices, insects spread their rav- 

 ages much faster than by the legs and wings provided by Mother 

 Nature. 



PHYSIOLOGICAL STRAINS OR VARIETIES 



Plant breeding and exploration have resulted in great assemblages 

 of not only many kinds of plants, but also of many strains of these 

 plants. One needs only to think of the many kinds of apples, peaches, 

 plums, and cherries; of the many kinds of wheat, corn, grain 

 sorghums, and of most every other variety of crop grown. It has 

 been found that there are different strains of the insects, which 

 strains are geographically distributed according to the crop. 



