48 



CIRCULAR 9 



S. DEPARTMENT OF AGRICULTURE 



Tennessee Valley Authority (TVA), and the method was employed for 

 several years for control of anopheline larvae on the extensive reservoir 

 system along the Tennessee River. Against these surface-feeding 

 larvae the exhaust-generated aerosols were effective at very low 

 dosages. The visibility of the heavy smoke-fog was also of aid to the 

 pilot in covering an area. The droplets were so fine, however, that 

 only a small portion of the solution, averaging 10 percent or less, 

 reached the water, the rest drifting away from the target areas. Sub- 

 sequently the spray-boom type of equipment was adopted by TVA 

 in place of the exhaust generator, as it caused more of the spray to 

 reach the mosquito-breeding areas. 



Helicopters. — Considerable experimental work has been done with heli- 

 copters for aerial dispersal of insecticides. Either boom-tj^pe equipment 

 (fig. 20), thermal smoke generators (fig. 21), or dust hoppers are used. 

 In general performance they compare favorably with fixed-wing air- 

 planes and are superior against some kinds of insects, at least in certain 

 situations. The advantages of helicopters lie in their great maneu- 

 verability, variable speed, strong downdraft at low speeds, and ability 

 to land or take off in a small space. These characteristics make it 

 possible to treat pockets and other difficult areas inaccessible to con- 

 ventional aircraft, as well as to base operations close to the treatment 

 areas independently of prepared landing strips, and thus reduce the 

 amount of nonspraying time. The most important disadvantages are 

 their high initial and maintenance cost, low cruising speed, small pay 

 load, and the small number of experienced pilots available. 



,**. 





Figure 20. — Helicopter equipped with spray b 



