for general household use, because they give quick knock-down, are 

 practically nonpoisonous to man and pets, and are not likely to damage 

 furniture, draperies, or clothing. Pyrethrum sprays now contain 

 piperonyl butoxide, ^-Propyl Isome, sesame oil, or some other chemical 

 that increases their effectiveness. 



Several organic thiocyanates, which are synthetic chemicals, can 

 also be used in space sprays. Sometimes these materials are combined 

 with pyrethrum. DDT or methoxychlor is now included in some 

 pyrethrum or thiocyanate space sprays. 



Some fly sprays are graded according to their effectiveness against 

 house flies. The grades are B, A, and AA, the last being the strongest. 

 Ungraded sprays may be of excellent quality, but when the consumer 

 buys graded sprays he can be sure of their quality. 



Space sprays with particles of insecticide so fine that they remain 

 floating in the air for several minutes are called aerosols. They may 

 be produced by the use of a liquefied gas under pressure, as in the 

 aerosol bombs, or with mechanical or thermal atomizers. The 

 common killing agents in aerosols are pyrethrum and DDT or 

 methoxychlor. 



Residua! Sprays 



The greatest benefit from some of the new insecticides is obtained 

 when they are applied as residual sprays to surfaces where flies crawl 

 or rest. When properly applied in the right amount, some of them 

 remain effective for several weeks or months. The flies are killed 

 simply by their feet coming in contact with the sprayed surface for 

 a short time. Residual sprays are important in the control of flies 

 in and around buildings. 



During the first several years that DDT was used, one application 

 of a residual spray killed all flies that came in contact with the treated 

 surface at any time during an entire season. Recently flies in many 

 areas have developed a marked resistance to DDT. These flies may 

 also be more difficult to control with some of the insecticides now used 

 as substitutes for DDT. 



Apply residual sprays with hand or power sprayers operating at 

 low pressures (less than 100 pounds per square inch) . High pressures 

 cause waste, as the spray is broken up too fine and rebounds to create 

 a mist. The object is to moisten the surface without causing run-off. 

 You can best do this by using a nozzle that will give a flat or fan-type 

 spray. Hold the nozzle about 18 inches from the surface and move 

 it up and down the wall so as to moisten the surface evenly. One to 

 two gallons will cover about .1,000 square feet. 



Around Homes 



Outside the house. — Apply residual sprays to screens, porches, gar- 

 bage cans, and other places outside the house where flies gather. For 

 this purpose use DDT, methoxychlor, lindane, or chlordane. 



You can generally obtain DDT and methoxychlor as wettable pow- 

 ders or as emulsion concentrates at different concentrations. Both 

 materials are recommended for use around homes at 2.5 percent 

 strength for suspension sprays and 5 percent for emulsion sprays. To 

 prepare a 2.5-percent suspension add 2 pounds of a 50-percent wettable 

 powder to 5 gallons of water. One gallon of a 25-percent emulsion 

 concentrate to 4 gallons of water will make a 5-percent emulsion. 



