THE MOSQUITOES OP THE SOUTHEASTERN STATES 19 



Good maps are, of course, essential, and should be available both 

 in small scale for use as key maps and in large scale for showing in 

 detail the breeding places, ditching lay-outs, and natural topographic 

 features. The different areas and the individual breeding places 

 can then be given names or numbers for convenient reference to 

 the mosquito-collection and engineering notes. Aerial photographic 

 maps of rural or marsh areas are extremely valuable, as they show 

 the bodies of water and the types of vegetation. A note-card system 

 should be arranged and complete records kept of all inspection and 

 survey data. 



For breeding-place or other preliminary surveys when elevations 

 or exact locations are not required, the directions given by Hulse (69) 

 for preparing field maps in public-health work based on methods 

 employed in the military service are very useful. 



CONTROL OF MOSQUITO LARVAE 



Mosquito-control measures are usually directed against the larvae, 

 since this seems to be the most vulnerable stage in their life cycle. 



ELIMINATION OF BREEDING PLACES 



Where at all feasible, efforts are made to eliminate the breeding 

 places permanently by filling, drainage, or sanitation. 



Filling is frequently an economical method and gives permanent 

 relief when the fills are so graded as to leave no water-holding de- 

 pressions. Large hydraulic fills, however, usually show shrinkage 

 or surface cracks upon drying and may require one or more regrad- 

 ings to prevent mosquito breeding. 



Drainage undoubtedly has the widest application of the various 

 antilarval measures, especially in the control of the malaria carriers 

 and the salt-marsh species. The drainage of swamplands in the 

 United States has done much to reduce the malarious area and at the 

 same time has made the land suitable for agriculture. Drainage, or 

 ditching, purely for mosquito control, however, should be looked 

 upon as distinct from agricultural drainage, since it is directed mainly 

 toward the elimination of surface water during the time required 

 for larval development, or to aid in biological control. Compre- 

 hensive drainage plans, especially for malaria control, should be pre- 

 pared with the aid of trained engineers. 



Two phases of the drainage problem in mosquito control to which 

 attention has been called in recent years are its possible effects upon 

 wildlife and upon soil conservation. Through cooperative biological 

 studies efforts are being made to determine what measures may be 

 applied to large swamp areas, particularly those not close to centers 

 of population, which will disturb as little as possible the natural 

 breeding and feeding grounds of aquatic wild fowl and other desir- 

 able animal life without sacrificing the success of the mosquito- 

 control project. Specialists in soil conservation have also called 

 attention to the adverse effects of the drainage of natural upland 

 storage basins, the cleaning of stream channels, and the "brushing" 

 of stream banks, all of which increase the rapidity of run-off of flood- 

 water with consequent erosion that may cause serious damage to agri- 

 cultural lands. Such erosion is said to cause frequently a gradual 



