DISTRIBUTION OF DISEASE GEKMS 



111 



127. How to destroy mosquitoes. Since malaria and some 

 other diseases are carried only by mosquitoes, it is evident 

 that if we can remove the mosquitoes we shall be free from 

 danger of infection. These insects pass the early part of 

 their lives in ponds, lakes, and quiet water, and they cannot 

 reproduce if the water is drained away. Where such drain- 

 age is possible, it is a good method of guarding against the 

 diseases carried by mosquitoes. Another method of destroy- 

 ing these insects is to pour kerosene over the water. The oil 



FIG. 57. The yellow-fever mosquito (Stcgomyia) 

 Male at left ; female at right. After Howard 



spreads over the surface of the water and kills the eggs. The 

 larvae and pupae cannot secure air through the surface film of 

 oil, so they die ; the adults cannot get to the surface of the 

 water to lay more eggs, and if they get into the kerosene in 

 their attempt to lay eggs they get killed. Still another 

 method of getting rid of them is to subject them to their 

 natural enemies. Fish eat the larvae, and therefore the mos- 

 quitoes will be less abundant if the ponds are stocked with 

 fish. A very small body of water, such as that in an old tin 

 can or in a partially filled hoof print, may be ample for the 



