1902.] INSECTS RELATION TO AGRICULTURE. I95 



Waite which showed that some of our common varieties of 

 pears are wholly unable to fertilize themselves and require 

 pollen not only from another tree, but from a different variety, 

 in order to become fruitful. Mr. Waite was working with 

 the "fire blight," a' well-known disease of pear orchards. 



He found that the germs were carried from flower to flower 

 by insects, whereupon insects were entirely excluded from 

 access to the tree, with the result that the tree set no fruit. 

 This revelation of the fact must be regarded at least to agri- 

 culture and horticulture as one of the most important dis- 

 coveries made during the latter part of the nineteenth century. 

 Later observations have shown that many varieties of apples, 

 pears, cherries, peaches, apricots, and nearly all the plums and 

 grapes are self-sterile. Even if not self-sterile, insects are 

 the principal agents in carrying pollen from one tree to an- 

 other, and the scarcity of apples this year is, I doubt not, due 

 in large measure to bad weather at blooming time, so that the 

 insects could not visit the flowers. 



The following figures based upon conservative estimates 

 will give us some idea of the great losses caused to agriculture 

 by injurious insects. In 1854 the wheat midge, in New York, 

 caused injury to the amount of $15,000,000. In 1874 the 

 ravages of the Rocky Mountain locust occasioned a loss of 

 $100,000,000 in the four states of Kansas, Nebraska, Iowa, 

 and Illinois, and the chinch bug caused a loss of $60,000,000 

 throughout the United States in 1877. 



Dr. Riley estimated that the total amount of damage to 

 the agricultural products of the United States aggregates 

 between $300,000,000 and $400,000,000 annually, caused by 

 the depredations of noxious insects. Even in 1899 the total 

 loss to farmers and truck gardeners along the Atlantic coast 

 caused by the destructive green pea louse was estimated at 

 $3,000,000. 



The first half of the nineteenth century produced several 

 students of insects in America, among which the names of 

 Thomas Say and Thaddeus William Harris were especially 

 prominent. The injurious insects were studied by Harris, 

 and his report on the " Insects Injurious to Vegetation," first 

 published in 1841, has passed through several editions and 

 still remains a classic, though many of our present methods 

 of combating insect pests were, in Harris' time, unknown. 



