26 INSECTS AFFECTING VEGETATION 



adding the secondary losses which, in the case of the great staple 

 productions of the farm, follow any considerable shortage and ul- 

 timately add to the cost of living for every individual, in addition 

 to creating large commercial disturbances. Furthermore, the cost 

 of protection from insect damage has been considered only in the 

 case of one or two products of the farm. Another considerable in- 

 sect tax not estimated for is the direct loss and the cost of protec- 

 tion from domestic or household insect pests. Screening of houses 

 against mosquitoes or flies, protection from roaches, clothes moths, 

 and the ravages of the white ant and of various parasitic insects, 

 are a charge on every household. The white ant in Washington, 

 D. C., alone causes losses of thousands of dollars yearly, and it is 

 much more destructive in southern districts. If the smaller or 

 larger sums expended for protection from such pests were tabu- 

 lated for the whole country, the total would probably exceed $50,- 

 000,000, and might be double that amount. An omission perhaps 

 more important than any of these is the indirect loss to the produc- 

 ing and earning capacity of communities by diseases conveyed by 

 insects. For example, malaria and yellow fever are dependent solely 

 on certain species of mosquitoes, and typhoid fever is commonly 

 carried by house flies. The losses from all three of these diseases 

 are enormous, and in the case of yellow fever outbreaks, often al- 

 most beyond computation. With domestic animals the tick, re- 

 sponsible for Texas fever in the South, has been estimated to cause 

 an annual loss of $100,000,000, and other diseases of man and 

 domestic animals will undoubtedly be shown to depend exclusively 

 or largely on biting or other insects. In view of these omissions, 

 it is certain that the total of over $700,000,000 annual loss assigned 

 to insect pests in America is below^ rather than above the actual 

 damage. The lessening or prevention of this loss is the problem 

 for the economic entomologist to solve. (Rep. Y. B. U. S. D. A. 

 1904.) 



RELATION OP INSECTS TO DISEASE. 



It has been definitely ascertained that malaria and yellow fever 

 are transmitted to man by the bites of certain mosquitoes and that 

 one of the three chief sources of the transmission of the germs of 

 typhoid fever is the house fly. 



The old idea that malaria is caused by breathing the miasma 

 or mist of swamp has been exploded. Malaria is contracted only 

 through the bites of mosquitoes of the genus Anopheles. The dis- 

 ease is caused by the introduction into the blood, through the bite 

 of the mosquito, of many small one-celled animals which destroy 

 the red corpuscles of the blood of man. In order to avoid the dis- 

 ease it is only necessary to avoid the bites of the insects. Mosqui- 

 toes are bred in stagnant water mostly and can be prevented by 

 thorough drainage, where feasible or 'by spraying oil on the water. 

 Proper screening of habitations is also necessary. 



One of the most important of these disease-transfer relations of 

 insects which has been demonstrated is the carriage of yellow fever 

 by certain mosquitoes. The cause of yellow fever has always been 



