INSECTS AND DISEASES 397 



toes, for without their agency the disease would not spread 

 from person to person. 



Yellow fever. Yellow fever is also carried by mosquitoes. 

 The cause of this fever is believed to be an organism some- 

 what similar to that which causes malaria. The method by 

 which mosquitoes carry the fever is similar. During the 

 epidemic of 1878, there were twelve thousand deaths from 

 yellow fever in the United States. Since the part that the 

 mosquitoes play in carrying this disease has become known, 

 such effective measures have been taken to control the 

 disease, that in 1910 there was only one death from yellow 

 fever. 



These diseases are not carried by all mosquitoes. Malaria 

 is carried by only one genus, Anopheles, and yellow fever 

 only by Stegomyia. The common mosquito (Culex) , usually 

 found around our buildings in the northern states, does not 

 carry either of these diseases. 



Financial loss due to mosquitoes. But even the common 

 mosquito may be such a pest as to cause financial loss. 

 Where they are especially abundant, they cause a deprecia- 

 tion of the value of the real estate and prevent the develop- 

 ment of sections of the country which would otherwise be 

 available for suburban homes, summer resorts, and agricul- 

 tural pursuits. In some sections of southern New Jersey, 

 herds of cattle have been so pestered by swarms of mos- 

 quitoes that dairying had to be abandoned. 



As a minor matter, mention may be made of the expense 

 involved in providing screens, which Dr. Howard estimates 

 as amounting to $10,000,000 annually. 



In the northern United States where malaria seldom occurs 

 mosquitoes are nevertheless a great pest, as they drive people 

 indoors during the evening and deprive them of the use of 

 the outdoors at the best time of the year, so that even in 

 this section it is worth while to make an effort to get rid of 

 them. 



