24 MISC. PUBLICATION 336, U. S. DEPT. OF AGRICULTURE 



cally by impounding the water with dams to a depth sufficient to 

 overcome the aquatic vegetation (pi. 3, B). Periodic fluctuation of 

 the water level in such impounded areas is very important in re- 

 ducing the marginal growth and flotage. The impoundage of large 

 bodies of water for hydroelectric or other purposes, however, has in- 

 troduced serious problems in malaria control, and special legislation 

 has been enacted by Southern States covering the measures that must 

 be taken to prevent breeding of anopheline mosquitoes in such proj- 

 ects. The Tennessee Valley Authority has found it necessary to 

 provide for an extensive program of Anopheles control in the im- 

 pounded areas on the Tennessee River. 



As previously mentioned, in planning extensive drainage opera- 

 tions careful consideration should be given to problems of wildlife 

 and soil conservation. 



The use of chemical larvicides, such as oil and paris green, is re- 

 quired for treating breeding areas that cannot be eliminated, and in 

 many places, owing to local conditions, this constitutes the main part 

 of the control program. Paris green dusted on the water will de- 

 stroy anopheline larvae because of their habit of feeding at the sur- 

 face and ingesting all small particles that lie on the surface film. It 

 is effective in such minute quantities that its use on ground waters 

 is not dangerous to animals. One or two percent of paris green is 

 used with an inert diluent such as fine road dust, hydrated lime, pul- 

 verized soapstone, or other available earths. It is applied with 

 various types of hand dusters or, for larger operations, with power 

 dusters mounted in boats. Under special conditions airplanes can 

 be used advantageously for treating large breeding areas (<££, 75, 76, 

 121) (pi. 1, B). In airplane dusting the proportion of paris green 

 is increased to 10 to 50 percent. As previously mentioned, calcium 

 arsenite, when produced commercially, may provide a cheap sub- 

 stitute for paris green. The applications of both arsenicals and 

 light oils must be repeated at about weekly intervals throughout 

 the breeding season, since these materials remain effective for only a 

 short period. 



An adult anopheline density index (78), obtained by periodic 

 counts of the numbers present in favorable daytime resting places 

 (inside and underneath dwellings, in stables, outhouses, etc.), is 

 highly useful in measuring the effectiveness of the control operations. 



THE DOMESTIC MOSQUITOES (AEDES AEGYPTI AND CULEX QUINQUEFASCIATUS) 



Urban antimosquito campaigns usually combine control measures 

 against the yellow-fever and the southern house mosquitoes, and, 

 although their practical control offers no insurmountable difficul- 

 ties, continuous efforts and expense are required to keep the num- 

 bers reduced. These species differ considerably in breeding habits, 

 especially as regards polluted waters and ground pools, although 

 rain barrels and similar water containers are important breeding 

 places for both. Where the water in these receptacles is required 

 for domestic purposes, the barrels should be kept tightly covered 

 and the water drawn from a spigot at the bottom; otherwise they 

 require weekly emptying or treatment with oil, either of which is 

 likely to be neglected. When larvae are present, spraying the sur- 

 face with a small amount of kerosene or a pyrethrum fly spray is ef- 



