234 



SCIENCE. 



[N. S. Vol. IX. No. 216. 



Insects are injurious : 



1. As destroyers of crops and other val- 

 uable plant life. 



2. As destroyers of stored foods, dwell- 

 ings, clothes, books, etc. 



3. As injuring live stock and other useful 

 animals. 



4. As annoying man. 



5. As carriers of disease. 

 Insects are beneficial : 



1. As destroyers of injurious insects. 



2. As destroyers of noxious plants. 



3. As pollenizers of plants. 



4. As scavengers. 



5. As makers of soil. 



6. As food (botli for man and for poultry, 

 song birds and food fishes) and as clothing, 

 and as used in the arts. 



DESTEOYBRS OF CEOPS AND OTHER USEFUL 

 PLANTS. 



"In 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 thous- 

 ands 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 al- 

 most as early as there is any record of agri- 

 culture 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 agricul- 

 tural pessimist. 



At the present time almost every culti- 

 vated 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 counti'y 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 

 startling figures. 



The actual damage which is done by in- 

 sects in this way is difiicult to express. 

 Many attempts have been made by writers 

 on economic entomology to expi-ess it in 

 money values. For example, it was esti- 

 mated by the late Professor Riley that the 

 average annual damage to cultivated crops 

 by injurious insects in the United States 

 amounted to three hundred millions of dol- 

 lars. The loss from the ravages of one 

 species alone, the chinch bug, during one 

 year was estimated at sixty millions of 

 dollars. 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 enhanced value of the portion of the 

 crop which remains. Even in the case of 

 an individual 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 successful 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 tlie grain crop of 

 the country was said to have been damaged 

 to the extent of sixty millions of dollars 

 it is safe to say that the total price gained 

 for the crop was as great as it would other- 

 wise have been. These estimates of dam- 

 age, therefore, would much better be ex- 

 pressed in terms of bushels, or some other 

 measure, than in money value. 



It is this aspect of our subject, the dam- 

 age done by injurious insects to agriculture, 

 that has given rise to the comparatively 

 new branch of applied science which we 



