CHAPTER XIII 



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 clone 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 Iowa, 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 Jose 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 is 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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