INSECTICIDES AND REPELLENTS 



33 



Figure 4. — Outdoor spraying with a DeVilbiss paint sprayer. 



similar way. Even with the finest nozzle it is difficult to cover an acre 

 adequately with less than 5 or 6 quarts because of the rapid discharge 

 and the coarse droplet size. 



Liquefied-gas aerosols. — The standard DDT-pyrethrum aerosol bomb 

 may be used to reduce mosquitoes in thickly wooded areas in the same 

 way as described for space sprays. The aerosol is released as the oper- 

 ator walks back and forth along parallel swaths about 20 feet apart. 

 Because the particles tend to rise and the mosquitoes usually rest in 

 the brush close to the ground, it is best to tie the bomb to a stick 

 and hold it within a few inches of the ground. The contents of a 1- 

 pound bomb (No. 1, table 3) have controlled salt-marsh mosquitoes 

 over an acre or even more, where it was possible to take advantage of a 

 slight air movement to drift the aerosol slowly through the vegetation. 



Power hydraulic sprayers. — For treating large areas power-operated 

 sprayers and other types of power equipment may be employed. 

 They are used chiefly for the treatment of occupied areas and installa- 

 tions where roads or streets are available along which the vehicles 

 carrying the equipment may be driven. The spray is released on the 

 downwind side of the street, and moderate breezes up to about 10 

 m. p. h. aid the drifting of the fine droplets across country. 



