226 



LIFE 0-N THE EARTH 



pean corn borer, the larva of another moth, threatens 

 to become a serious pest. It is believed to have been 

 introduced into this country about 1917 and it has al- 

 ready spread as far west as Indiana. Since the larva 

 lives inside the stalks of corn and other plants, the 

 method of control is to burn or destroy in some other 

 way the plant remains in which the insect is living. 

 During the summer, in the eastern part of the United 

 States, it is not an uncommon thing to be stopped on 



Courtesy U. S. Department of Agriculture 



FIG. 357. LIFE HISTORY OF THE JAPANESE BEETLE 



the road by an officer, for an inspection of your car, 

 to see whether you are carrying any plants that may 

 spread the corn borer into some uninfested locality. 

 The Japanese beetle, introduced into New Jersey 

 about 1916, is another foreign pest. The larva lives 

 in the ground and eats grass roots while the adult 

 insect feeds on fruit and leaves of many different 

 kinds of plants. It multiplies rapidly and is gradually 

 spreading to other states. Cultivation of the soil kills 

 many of the larvae, and some of the adults are killed 

 by poisoning. For various reasons, however, these 

 methods have not been very successful, and at the 

 present time quarantine is being attempted to prevent 



the spread of the pest while government experts 

 search for other methods of control. 



How are insect pests controlled? Intelligent control 

 of insects requires a thorough knowledge of their 

 life histories. People who specialize in the study of 

 insects must become familiar with every stage of the 

 life history of a pest and then determine how it can be 

 controlled. Natural enemies are used to control cer- 

 tain insect pests. This method is called biological control, 

 and it promises to play an important part in the con- 

 trol of insects in the future. At one time the orange 

 and lemon industry of California was threatened with 



California Fruit Growers Exchange 



FIG. 358. RIDDING TREES OF HARMFUL INSECTS 



The trees are covered with canvas; then poisonous gases are 

 pumped under the covering. 



extinction because of a pest known as the cottony 

 cushion scale. Mr. Albert Koebele of the U. S. Depart- 

 ment of Agriculture, while collecting insects in Aus- 

 tralia, noticed that this cottony cushion scale was 

 being destroyed by the Australian ladybird beetle. 

 Knowing this beetle was not a native of the United 

 States, he introduced it into California, where it be- 

 came so numerous that the cottony cushion scale was 

 soon under control. Today the ladybird beetle is raised 

 by the state of California, and whenever the cottony 

 cushion scale becomes abundant some of the beetles 

 are released. The result is complete control of the 

 scale in a short time. Many artificial methods such as 

 spraying, traps, crop rotation, and cultivation are also 

 employed to control insect pests. 



Spraying. This method of controlling injurious in- 

 sects depends upon the ability of the substance used 

 in the spray to kill the insect either by contact or by 

 internal poisoning. In the case of insects like the Colo- 

 rado potato beetle, which eat the leaves of plants, an 



