Airplane Dusting in Control of Malaria Mosquitoes 3 



'• parting,*' but the former was found to be too light in weight and 

 likely to drift away without settling. The " parting " contains 2 per 

 cent of oils and is relatively waterproof, but unfortunately it did 

 not improve the floating qualities of the Paris green. 



Other carriers used were ordinary road dust and a mixture of lime 

 and flour. In the few tests in which these were employed, no 

 evidence was obtained of a separation of the carrier and the arsenical : 

 but the tendency of the flour and lime to become packed in the 

 hopper, owing to the vibration of the plane, was a drawback to its 

 use. Although road dust is a satisfactory carrier for hand applica- 

 tions, it seemed desirable to obtain a substance more uniform in 

 quality and more certain as to source of supply for any airplane work 

 on a large scale. 











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Fig. 1. — Dusting plane flown across open field to determine the spread of the Paris 

 green and dust* mixture under the nx>st favorable conditions. Plane flying about 

 15 feet above the ground 



PRELIMINARY EXPERIMENTS TO DETERMINE DISTRIBUTION OF 

 THE DUST ON THE GROUND AND MINIMUM KILLING DOSAGE 



In preliminary ground experiments the approximate minimum 

 concentration of Paris green necessary to kill the larvae was deter- 

 mined by placing side by side a series of dry glass plates 2 by 3 

 inches in size and open dishes containing water and Anopheles larvae 

 and dusting the two with varying quantities of Paris green with a 

 hand duster. The larvae were then watched for 24 hours to deter- 

 mine their mortality, and the numbers of granules of the Paris green 

 per square inch were counted on the glass plates with a low-power 

 microscope. 



Following this the first airplane tests were made over open ground, 

 glass plates being used as a means of determining the drift of the 

 dust and the quantity which settled to the ground. In these tests, 

 in which various mixtures were used, the plane was flown from 15 

 to 30 feet above the ground (fig. 1) and at right angles to the direc- 



