588 MAN AS A CONQUEROR 



will not feed, or else to plant a given crop earlier or later so it will 

 mature a little ahead or behind the ai)pearance of the insect enemy. 

 Such, for example, is the early planting of cotton in the southern 

 areas where the boll-weevil is a pest, or the late planting of spring 

 wheat in order to escape damage from the Hessian fly. 



(3) A third method of fighting insects comes through a study of 

 their feeding habits. Beetles, caterpillars, and locusts bite holes in 

 plants and chew their food, whereas bugs suck the juices of plants. 

 In the case of the former, poisons are sprayed on the leaves which are 

 eaten by the insect. Such poisons as lead arsenate or Paris green 

 are used against the potato beetle and cabbage moths. In the case of 

 the sucking insects, an oil spray or emulsion, that clogs up the spiracles 

 and eventually kills them, is used. Mixtures containing nicotine, oil, 

 soap, or kerosene are called contact poisons. In addition to these 

 methods, picking off or shaking the insects into pans and then de- 

 stroying them, drenching planted areas with creosote or other sub- 

 stances, or banding tree trunks with tar are employed. 



The battle between man and his insect foes has only begun. Each 

 year sees new developments in both agriculture and animal husbandry, 

 and each year, with an increase of food plants and new strains of food 

 animals, new species of plant and animal parasites as well as of pests 

 are appearing, either introduced from other countries or developed 

 in nature's own way from mutants or crosses. Will man ultimately 

 win the battle ? Who knows ? 



SUGGESTED READINGS 



East, E. M., Biology in Human Affairs, McGraw-Hill Book Co., 1931. 



An interesting and authentic survey of biological knowledge as it is ap- 

 plied for the benefit of mankind. Written by a dozen leading specialists 

 in the fields of genetics, medicine, foods, public health, and psychology. 



Gager, C. S., General Botany, P. Blakiston's Son & Co., 1926. 



A general botany with much economic material included. Valuable for 

 reference. 



Henderson, J., The Practical Value of Birds, The Macmillan Co., 1927. 

 Useful for reference. 



Howard, L. 0., The Insect Menace, Century Co., 1934. 



The title suggests the contents. An interesting discussion of a timely 

 subject by an eminent authority. 



Metcalf, C. L., and Flint, W. P., Insects, Man's Chief Competitors, Williams 

 and Wilkins, 1932. 

 The title explains the point of view. 



