MAN'S CONQUEST OF NATURE SSI 



Methods of Control 



It might seem a hopeless fio-ht that man is waging with his insect 

 foes, especially as he is constantly introducing new species and just 

 as constantly providing more food for them. It seems, indeed, like 

 an endless chain of difficulty. Nevertheless, man has his brains and 

 his social inheritance to aid in the fight. He has organized liis 

 forces through such agencies as the United States Department of 

 Agriculture and its various bureaus, state agricultural agencies, 

 public and private research laboratories, as well as control and quaran- 

 tine offices in various parts of the country. A very large number of 

 highly trained scientists are at work, both in this country and abroad, 

 studying life histories, looking u}) plants fitted to withstand insect 

 attacks, and running down parasitic enemies of harmful insects. 



Methods of control have been worked out along several lines. 



(1) Natural enemies of insects which do harm are found and 

 encouraged. Many of these enemies are already "on the job." 

 Insect-eating birds, toads, frogs, and snakes, as well as insect- 

 feeding mammals, are examples. Many insects are attacked by 

 parasitic fungi. To find enemies for imported crops it is often nec- 

 essary for entomologists to go to the original country from which a 

 given plant has come in order to study its insect enemies there, and 

 to note how these are kept in check. The historic example of the 

 discovery of a ladybird beetle as an enemy of the cottony-cushion 

 scale, which threatened the orange industry of California, may be 

 cited. In this case a natural enemy of the destructive scale was 

 found in Australia, which, when imported to California, soon had 

 the situation under control. Our latest enemy, the Japanese beetle, 

 has possibility of control through an imported roundworm, while 

 our native birds are also beginning to include it in their dietary. 

 The importation of such insects as new species of ichneumon flies, 

 that parasitize many harmful caterpillars, or of damsel flies or man- 

 tises, both of which feed on injurious insects, are examples of this 

 kind, of control. Scouts from the Bureau of Entomology in the 

 Department of Agriculture are now at work in foreign coimtries 

 seeking parasitic enemies of the European corn borer, the Mexican 

 cotton boll-weevil, and our worst forest pests. 



(2) A second method used in fighting insect pests is to study the 

 life histories of both the pest and the crop which it attacks, and then 

 either to change the crop in a given area to another on which the pest 



