42 CIRCULAR 9 7 7. U. S. DEPARTMENT OF AGRICULTURE 



side walls of barracks and other living quarters with DDT solution, 

 emulsion, or suspension at the rate of 200 mg. of DDT per square 

 foot. The recommended application is 1 gallon of a 5-percent solu- 

 tion or emulsion per 1.000 square feet of surface. When suspensions 

 are used, a concentration of 3.75 percent of DDT from a 75-percent 

 wettable powder is advocated to reduce clogging of the nozzle. To 

 give the 200-mg. deposit the amount of spray per 1,000 square feet 

 is then increased to 1}{ gallons, or the amount of wall surface per 

 gallon is reduced to 750 square feet. A single application per season 

 is sometimes sufficient, but re-treatment after 2 or 3 months may be 

 required where walls are porous or dusty and under other adverse 

 conditions. 



Emulsions, oil solutions, or suspensions may be used for residual 

 sprays. Suspensions are usually more effective, especially on porous 

 surfaces, but they leave a visible residue, which is objectionable on 

 finished surfaces. For use on painted or papered walls, solutions in 

 refined kerosene are preferred to either emulsions or suspensions. 



Chlordane and lindane are also effective in residual sprays against 

 mosquitoes. Both materials show considerable vapor toxicity, but 

 they are not nearly so long lasting as DDT. Dieldrin is also highly 

 effective when applied in this manner and is longer lasting than either 

 chlordane or BHC. However, it has not yet been fully evaluated for 

 control of adult malaria mosquitoes. In the specifications covering 

 emulsifiable concentrates of these materials (Nos. 7, 9, and 10) the 

 recommended concentrations in the emulsions for use in indoor 

 residual sprays are chlordane 2 percent, lindane 1 percent, and dieldrin 

 0.5 percent. When they are applied at the rate of 1% gallons to 

 1,000 square feet of wall surface, the respective dosages are 100, 50. 

 and 25 mg. per square foot. Because of their vapor toxicity these 

 insecticides are not approved for complete coverage of walls in build- 

 ings, but may be used for spot treatment of infested areas. 



Residual sprays may be applied with the standard pressure cylinder 

 or power sprayers (fig. 14). The choice will depend on the size and 

 number of buildings to be treated, their accessibility, and the means 

 of transporting the equipment. A fan-type nozzle is preferable, but a 

 cone-type nozzle giving a coarse wet spray may be used. A finely 

 atomized spray is not efficient for this purpose. The spray nozzle 

 should be held 12 to 18 inches from the surface and moved up and 

 down or back and forth to cover the wall in successive strips. 



AIRPLANE APPLICATIONS 



Airplanes were first employed experimentally in 1923 by members 

 of the then Bureau of Entomology for the control of malaria mosquito 

 larvae in large swamp areas with paris green dusts. They were 

 later used by the Tennessee Valley Authority and other agencies. 

 The development of DDT greatly stimulated interest in the use of 

 airplanes as, a means of controlling culicine as well as anopheline 

 mosquitoes. Workers at the Orlando laboratory demonstrated for 

 the first time that adult mosquitoes could be controlled economically 

 and effectively over large areas by aerial sprays. The high toxicity 

 of DDT to both larvae and adults made it possible to treat large areas 

 with few loadings of the plane, and thus keep costs low. 



