INSECTICIDES AND REPELLENTS 59 



In deep-pit latrines that are tight and fairly dry, the fumes of para- 

 dichlorobenzene will not only destroy the larvae but prevent oviposi- 

 tion by repelling the adults. The granular material is applied at the 

 rate of about 8 pounds per eight-seat latrine initially and 2 pounds 

 twice a week thereafter. Sodium arsenite is used at a concentration 

 of about 1 percent and is more effective than paradichlorobenzene in 

 wet or shallow latrines. However, it is a deadly poison and should 

 be used only with proper precautions and not at all if there is a possi- 

 bility of contaminating ground water supplies or poisoning growing- 

 plants. If a sodium arsenite powder is available, it may be dissolved 

 in water at the rate of about 1 pound to 10 gallons. A solution con- 

 taining 54 percent of sodium arsenite is a stock item (No. 17) and is 

 diluted 1 to 53 for treating latrines. 



Oil solutions containing 5 percent of DDT or BHC are applied at 

 the rate of 1 quart per seat per week. The treatments are more 

 effective, especially in overloaded latrines, if they are divided into 

 two or more applications per week. If a lindane emulsion is used, a 

 concentration of 1 to 2.5 percent is suggested for preliminary tests to 

 determine the minimum effective dosage and interval of treatment. 

 A DDT-xylene emulsion was found to be more effective than a fuel 

 oil solution, but it should not be used in enclosed spaces because of 

 the danger of explosion when the xylene fumes are concentrated. 

 However, the DDT nonexplosive emulsifiable concentrate, now a stock 

 item (No. 8), may be used in latrines. 



Residual sprays should be applied to the walls of the latrine and 

 vault to reduce the number of adults that visit the latrine or emerge 

 from the fecal medium in spite of the larvicides. 



All these insecticides except paradichlorobenzene may be used for 

 spraying fly-breeding places in the open, such as garbage dumps, 

 manure piles, and other refuse, as well as dead bodies or animal 

 carcasses that become infested before proper disposal can be made. 

 Such bodies should be thoroughly sprayed on all sides as well as the 

 ground underneath and for several feet around them. If sodium 

 arsenite is used, a concentration of 2.5 percent is recommended. A 

 5-percent BHC emulsion with benzene as the solvent is also highly 

 effective and rapid in action. The sprays will not destroy larvae 

 inside the corpse or carcass, but the DDT and BHC residues should 

 kill most of the adults feeding or ovipositing on the bodies and also 

 those that emerge from escaping larvae. 



CONTROL OF HUMAN LICE AND SCABIES 



Three kinds of lice infest man — the body louse, the head louse, and 

 the crab louse. They differ considerably in habits and therefore re- 

 quire different methods of control. Since the body louse is the vector 

 of epidemic typhus and other diseases, emphasis has been placed on 

 development of measures for its control. The head louse is closely 

 related to the body louse and presumably may also transmit disease. 

 The crab louse is not known to transmit any disease, but does cause 

 much irritation of the skin. All three species are cosmopolitan in 

 distribution. 



Scabies, or human itch, is caused by the itch mite, which burrows 

 through the outer layer of the skin. The disease is common, but its 



