552 THE ECONOMIC STATUS OF INSECTS AS A CLASS. 



DESTROYERS OF CROPS AND OTHER USEFUL PLANTS. 



Iii the present balance of nature one of the chief functions of insect 

 life is to keep down superabundant vegetation. Almost every kind of 

 plant has its insect enemies, and has had such enemies for many thou- 

 sands of years. So soon as man began to make an effort to upset 

 nature's balance by cultivating certain plants at the expense of others 

 he encountered nature's opposition by means of the increase of insect 

 enemies of the particular plant cultivated, and almost as early as there 

 is any record of agriculture in literature there is also mention of the 

 destruction to crops caused by insects. Witness the writings of the 

 prophet Joel, who might almost be termed an agricultural pessimist. 



At the present time almost every cultivated crop has not only its 

 thousands upon thousands of individual insect enemies, but it is affected 

 by scores and even hundreds of species. A mere tabulation of the 

 insect enemies of the apple already recognized in this country shows 

 281 species, of clover 82 species, and of so new a crop as the sugar 

 beet 70 species. The insects of the vine, of the orange, of the wheat 

 crop, and, in fact, of all of our prominent staples, show equally start- 

 ling figures. 



The actual damage which is done by insects in this way is difficult 

 to express. Mauy attempts have been made by writers on economic 

 entomology to express it in money values. For example, it was esti- 

 mated by the late Professor Riley that the average anuual damage to 

 cultivated crops by injurious insects in the United States amounted to 

 $300,000,000. The loss from the ravages of one species alone, the 

 chinch bug, during one year was estimated at $60,000,000. While it is 

 true that the combined losses of individual growers might reach such 

 enormous sums as these, there is an element in the total loss which we 

 must not fail to take into consideration, and that is the enchanced value 

 of the portion of the crop which remains. Even in the case of an indi- 

 vidual a man may lose, for example, half of his crop through the work 

 of the chinch bug, and yet, through widespread damage by this insect, 

 the money value of the portion harvested may reach an amount almost 

 as great as would have been gained through the low prices of a suc- 

 cessful year of no insect damage. As this applies to an individual, it 

 applies much more strongly to a State or to the country at large, so that 

 even in the year when the grain crop of the country was said to have 

 been damaged to the extent of $60,000,000 it is safe to say that the 

 total price gained for the crop was as great as it would otherwise have 

 been. These estimates of damage, therefore, would much better be 

 expressed in terms of bushels, or some other measure, than in money 

 value. 



It is this aspect of our subject, the damage done by injurious insects 



