2 Department Circular 367, U. S. Dept. of Agriculture 



Considering the extent of the swamp areas in the region, the small 

 proportion of cultivated land, and the limited population, it did not 

 appear altogether likely that such a method would prove to be a 

 practical means of malaria control under these particular conditions. 

 Such swamp areas prior to drainage are, however, almost inaccessi- 

 ble to any other means of treatment, and it seemed entirely possible 

 that airplanes might be of practical use under similar or other con- 

 ditions where the per capita cost of the operations would not be 

 excessive. 



In the cotton-dusting work it has been found that, under favor- 

 able conditions, several hundred acres an hour can be treated by 

 a single plane and that the dust can be thoroughly distributed over 

 the fields. The swamp areas, however, present much more difficult 

 flying conditions than the open cotton fields, and the principal pre- 

 liminary questions to be decided were (1) whether the planes could 

 be safely flown over such areas and (2) whether the dust could be 

 released so as to reach the water surface in effective quantities. One 

 factor which appeared to favor the distribution of dust in such a 

 manner was that the direction of the air currents is usually down- 

 ward over woods and bodies of water, whereas over open ground it 

 is upward. 



The experiments were carried out during 1923 and 1924, Army 

 DeHaviland 4— B planes, operated by Air Service pilots, being used. 

 A light metal hopper designed to hold 300 pounds of calcium arsenate 

 was built into the rear cockpit, and the dust was released through 

 an opening provided in the bottom of the fuselage. 2 



THE INSECTICIDAL DUST USED 



Paris green appears to be the most promising larvicide available 

 for airplane dusting in control of Anopheles larvae, and it was the 

 arsenical used in all the experiments. It has proved to be as effective 

 as oil in control of Anopheles larvae, 3 is very much less costly than 

 oil, and can be applied in dry form suitable for distribution by air- 

 plane. Unfortunately it is not satisfactory as a general larvicide, 

 since it does not destroy the larvae of other mosquitoes which do not 

 have the surface-feeding habits of Anopheles, and it remains effec- 

 tive on the water for only a very short time. On the other hand, in 

 the quantities used, it is not poisonous to the insects and small fishes 

 which prey upon mosquito larvae. 



Since only a very small quantity of Paris green is necessary to kill 

 mosquito larvae, an inert dust of some sort was used as a diluent and 

 carrier. For the airplane mixtures a finely ground silica earth was 

 the diluent principally used. A " double-ground " product was uni- 

 form in quality and was found to have about the same density as 

 Paris green, a factor thought to be of possible importance because 

 of the strong air blast to which the mixtures are subjected when re- 

 leased from the hoppers and which would tend to separate substances 

 of different weights and composition. A much finer " air-float " 

 product from the same source was also tried, as well as foundry 



2 A description of earlier experiments with airplanes is given in IT. S. Dept. Agr. Bui. 

 1204, Dusting Cotton from Airplanes, by B. R. Coad, E. Johnson, and G. L. McNeil. 



3 M. A. Barber and T. B., Hayne. Arsenic as a larvicide for anopheline larvae. In 

 U. S. Pub. Health Serv., Pub. Health Rpt., vol. 36, pp. 3027-3034. 1921. 



