(3 Department Circular 367, U. S. Dept. of Agriculture 



work is required in making preliminary examinations and in check- 

 ing the results. 



A full description of the shallow swamp lakes found in this region 

 has been published recently by one of the writers 4 and will not be 

 repeated in detail here. In general, they are the principal sources 

 of Anopheles mosquitoes and as a rule consist of a central treeless 

 area of more or less permanent water, surrounded by a dense mar- 

 ginal growth of trees and brush. (Fig. 3.) The central area is usu- 

 ally overgrown with water chinquapin and water lilies (Xelumbo 

 and Castalia) and other smaller aquatic vegetation. In winter the 

 lakes become filled and the water spreads out into the woods, often 

 covering large areas and producing favorable conditions for mos- 

 quito breeding in spring and early summer. As the excess water 

 drains away or evaporates, the larvae are found in the more open 



Fig. 3. — One of the larger swamp lakes 



parts of the lakes away from the trees. The principal difficulty 

 anticipated in treating such areas was in reaching the larvse in the 

 wooded marginal zones. 



In the first of the three lakes selected, known as Field Lake, the 

 open part was something over a half mile in length and perhaps one.- 

 fourth as wide as long. Between the lake and a cleared pasture on 

 one side was a narrow fringe of flooded woods varying in width 

 from 50 to 200 feet. Breeding was prolific in this fringe and in 

 places in the open lake, under the thick growth of lilies and in mats 

 of mud plantain and Ceratophyllum. In preparing for the dusting 

 flights larval examinations were made at 10 or more points in the 

 part of the lake to be treated, and a glass plate was left on a floating 

 block at each of these " stations." From the plates it was possible to 



* G. H. Bradley. The natural breeding places of Anopheles mosquitoes in the vicinity 

 of Mound, La„ In. Amer. Jour. Trop Med., vol. 4, pp. 199-223, 1924. 



