CONTROLLING INSECT PESTS 405 



their time to the study of the general biology of insects, and 

 many of their bulletins and special reports are scientific papers 

 of much value to naturalists, as well as to the general public, 

 for whom they are primarily issued. Directions for obtaining 

 these bulletins and reports are given on page 419. 



Sometimes the fight against an insect pest can be carried on 

 successfully by one man in his own orchard or field, but more 

 often the whole community must co-operate if lasting benefits 

 are to be secured, because most of the insects so readily pass 

 from one place to another. The necessity for such co-opera- 

 tion is well illustrated in the fight against flies and mosquitoes. 

 One unclean stable, where the manure is left for a breeding place 

 for flies, may be a source of annoyance and danger to all the 

 homes in the community. For a successful campaign against 

 house-flies, all the members of the community must see to it 

 that there are no manure piles, open privy vaults, open garbage 

 cans or other places where the flies may breed and feed, while 

 a united effort should be made to trap and kill as many of the 

 adult flies as possible. Some mosquitoes, such as the yellow- 

 fever mosquito and others, breed only near houses and fly but 

 a short distance. In such instances a single person may free 

 his house from these pests by seeing that the mosquitoes 

 find no breeding places near. But many kinds of mosquitoes 

 fly for considerable distances, and the problem of their control 

 then becomes one for the community as a whole to deal with. 



NATURAL ENEMIES OF INSECTS 



Insects have many natural enemies which in many ways help 

 to control the injurious species. Indeed, were it not for this 

 condition many of them would increase so rapidly that they 

 would be wholly beyond the control of man. It is a significant 

 fact that with all our improved methods for fighting insects the 

 total amount of damage that they do to our crops is increasing 

 rather than decreasing. This is due in part to the introduction 

 of new pests, and in part to the more extensive and intensive 

 cultivation of crops. But the fact that we are changing the 

 natural conditions of vast areas and often destroying many of 



