INSECTS 235 



breeding of millions can be prevented. Brush and 

 other rubbish in orchards and forests are the breeding 

 places of many insect pests. The burning of such 

 breeding spots is an extremely effective method of 

 reducing insect enemies of orchards and forests. 



Rotation of crops. Insects that attack one kind 

 of crop may be starved to death by planting another 

 kind of crop on the land. Thus rotation of crops re- 

 duces the number of insects. Some crops may be 

 saved from insect attacks by early or late planting. 

 For example, if cotton is planted early, the bolls are 

 formed before the boll weevils have become numerous ; 

 and the late planting of wheat saves it from the Hes- 

 sian fly. 



QUESTIONS 



1. What are some of the most destructive insects? 



2. What insects are useful ? 



3. What are the most important insect enemies of wheat? 

 Of corn ? Of cotton ? Of fruit trees ? Of shade trees ? 



4. What are the five classes of insect pests ? 



5. What disease common to the United States is transmitted 

 by mosquitoes? What tropical disease is transmitted by a 

 mosquito of tropical regions? What other diseases are fre- 

 quently carried by insects? 



6. What cattle disease is transmitted by insects ? 



PRACTICAL EXERCISES 



i. Study the life history of the mosquito by observation. In 

 the fall or spring place a tub of rain water out of doors, and each 

 morning look for floating masses of mosquito eggs. Each mass 



