PROBLEM 3. H01V We Try to Solve Our bisect Problems 397 



into trouble, not by importing the insect beetles fed on the new crop and in- 



but by importing a new crop. The Colo- creased rapidly, causing many thousands 



rado potato beetle is native to the of dollars of damage annually. You can 



United States. Before the potato was in- see that we may create an insect prob- 



troduced this beetle fed only on weeds lem when we import insects without 



and was of no importance to us. When their natural enemies or plant a new crop 



we began the cultivation of potatoes, the on which native insects feed. 



Questions 



1. State at least five ways in which insects are harmful to us. 



2. Explain how we create an insect problem by planting crops on a 

 large scale. What plant is a good example of this? 



3. Explain how insects are harmful not only to the farmer but to all of 

 us. What is the extent of their damage? 



4. What is the work of the Bureau of Entomology? What agencies assist 

 in this work? What facts must entomologists know about each insect? 



5. Give the life history of the European corn borer. Show how a knowl- 

 edge of its life history can help in its control. What other methods 

 may be used? 



6. Describe briefly the life history of the chinch bug and the gypsy 

 moth and explain how we can partially control each insect. 



7. What are stomach poisons and how are they used? In which stage do 

 they kill the insect? Explain. Name two insects we control in this way. 



8. Against which insects are contact poisons used? How do they work? 

 What is the advantage of DDT? Explain the life history of the clothes 

 moth. 



9. Which vertebrates and which invertebrates do we try to use as our 

 allies against insects? Name two insects which we try to control 

 through using natural insect enemies. Why are imported insects often 

 particularly difficult to keep in check? Name five such serious insect 

 pests. Give some idea of the harm done by the Japanese beetle. 



10. How did the planting of potatoes result in an insect problem? 



Exercises 



1. How does a study of the mouth parts of an insect help to determine 

 the methods of combating it? If you have not already done so, study the 

 mouth parts of the grasshopper and the moth or butterfly (see p. 68). 

 Describe what you see. Which can do more damage to crops? Why? You 

 must remember, however, that the moth has other stages in its life history. 

 See Exercise 2. 



2. In which stages of their lives are grasshoppers, moths, and beetles 

 most harmful? If you are not well acquainted with the life histories of 

 grasshoppers and moths refer to Unit I, Problem i. Study and describe 

 actual specimens of these insects. 



