INSECTICIDES AND REPELLENTS 



37 



Mist blowers. — Several types of mist blowers have been developed 

 especially for the control of flying insects. In one type the liquid 

 is pumped to the spray head at low pressure, where it is delivered 

 into the center of a high-speed air blast (fig. 8). Some mosquito- 

 control organizations prefer mist blowers over fog machines or high- 

 pressure hydraulic sprayers for treating residential sections for adult 

 mosquitoes. Emulsions are frequently used instead of oil solutions 

 to avoid injury to vegetation. The output is greater than that of fog 

 machines, and the residue left on the vegetation may destroy mos- 

 quitoes that move into the area after the spraying. Sprays containing 

 1 to 5 percent of DDT are usually employed. This type of machine 

 may be used also for larvicide applications, especially where the 

 breeding places are fairly wide and are best covered by a wind-drifted 

 spray. 



In another type of mist blower, called a Microsol machine (fig. 9), 

 the spray is finely atomized by means of rotating or spinning disks 



jMmm- 



Figure 9. — Microsol machine mounted in a jeep. 



and then dispersed by an air blast. This machine is sometimes called 

 a mechanical aerosol generator, but the average droplet sizes fall more 

 nearly into the category of a mist, i. e., greater than 50 microns in 

 diameter. A small portable electric model (fig. 10) for use inside 

 buildings, however, is said to give a large proportion of droplets 

 within the accepted aerosol range. 



Thermal jog generators. — A thermal fog generator (fig. 11) has been 

 developed especially for the area control of adult mosquitoes and other 

 flying pests. Heat is employed to break up the liquid into fine drop- 

 lets, which are borne across country or through woods as a dense 

 fog. Several machines based on this principle are available. Some 

 of them have a combustion chamber in which the air is heated by a 



