52 ECONOMIC ENTOMOLOGY 



Stegomyia Mosquito and Yellow Fever: 



The demonstration of the causal relation between the Stegomyia 

 mosquito and yellow fever is another interesting story, and was worked 

 out mainly by Major Walter Reed of the U. S. Army Medical Service 

 in Cuba in 1900 and 1901. In his experimental camp Major Reed 

 and his associates proved that yellow fever could not be transmitted 

 by contact with yellow fever patients, but only by the bites of infected 

 mosquitoes and by the artificial injection of diseased blood. The 

 causal organism has not yet been discovered on account of its being a 

 filterable virus. It is known, however, that a 12-day incubation 

 period is required in Stegomyia before its bite becomes infectious to a 

 second person. Moreover, the mosquito can obtain infected blood 

 from a patient during only the first three days of his disease. 



Based on these facts, the control of yellow fever has become an 

 easy matter. The patients are isolated as soon as the disease appears, 

 and standing water in which Stegomyia might develop is treated with 

 kerosene. Besides, all rooms in the building and adjacent buildings 

 are fumigated, for the purpose of destroying living mosquitoes. 



Culex Mosquito and Filariasis: 



The tropical disease, filariasis, is caused by a minute nematode 

 worm, Filaria, which lives in the blood of man and certain species 

 of Culex (C. fatigans). The worms escape from the mid-intestine of 

 the mosquito into the muscular tissue where they grow for two or three 

 weeks. They then migrate to other portions of the body and often 

 collect at the base of the proboscis, whence they are carried into the 

 human blood circulation. Sometimes the worms become three or 

 four inches long and obstruct the lymphatic canals, causing elephan- 

 tiasis, characterized by enormous sweUings of the legs, arms and other 

 parts of the body. 



body." ga. Mature microgametocyte, preparatory to forming microgametes. gb. 

 Resting cell, bearing six flagellate microgametes (male). lo. Fertilization of a 

 macrogamete by a motile microgamete. The macrogamete next becomes an ookin- 

 ete. II. Ookinete, or wandering cell, which penetrates into the wall of the stomach 

 of the mosquito. 12. Ookinete in the outer region of the wall of the stomach, i.e., 

 next to the body cavity. 13. Young oocyst, derived from the ookinete. 14. Oocyst, 

 containing sporoblasts, which are to develop into sporozoites. 15. Older oocyst. 

 16. Mature oocyst, containing sporozoites, which are liberated into the body cavity 

 of the mosquito and carried along in the blood of the insect. 17. Transverse section 

 of salivary gland of an Anopheles mosquito, showing sporozoites of the malaria para- 

 site in the gland cells surrounding the central canal. 



1-6 illustrate schizogony (asexual production of spores); 7-16, sporogony (sexual 

 production of spores). {After Grassi atid Leuckarl, by permission of Dr. Carl Chun.) 



