CHAPTER XTi 
INSECTS IN RELATION TO MAN 
A great many insects, eminently successful from their own 
standpoint, so to speak, nevertheless interfere seriously with 
the interests of man. On the other hand, many insects are 
directly or indirectly so useful to man that their services form 
no small compensation for the damage done by other species. 
Injurious Insects.—Insects destroy cultivated plants, infest 
domestic animals, injure food, manufactured articles, etc., and 
molest or harm man himself. 
The cultivation of a plant in great quantity offers an un- 
usual opportunity for the increase of its insect inhabitants. 
The number of species affecting one kind of plant—to say 
nothing of the number of individuals—is often great. Thus 
about 200 species attack Indian corn, 50 of them doing notable 
injury; 200 affect clover, directly or indirectly; and 400 the 
apple; while the oaks harbor probably 1,000 species. 
The average annual loss through the cotton worm, 1860 to 
1874, was $15,000,000, according to Packard; the loss from 
the Rocky Mountain locust, in 1874, in lowa, Missouri, Kan- 
sas and Nebraska, $40,000,000 (Thomas) ; and the total loss 
from this pest, 1874 to 1877, $200,000,000. The loss through 
the chinch bug, in 1864, was $73,000,000 in Illinois alone, as 
estimated by Riley. The ravages of the Hessian fly, fluted 
scale, San José scale, gypsy moth and cotton boll weevil need 
only be mentioned. 
At times, an insect has been the source of a national calam- 
ity, as was the case for forty years in France, when Phylloxera 
threatened to exterminate the vine. In Africa the migratory 
locust 1s an unmitigated evil. 
Probably at least ten per cent. of every crop is lost through 
the attacks of insects, though the loss is often so constant as 
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