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



tion of the wind and to two lines of glass plates placed at intervals 

 across an open field. In the best of the trials it was found that a 

 strip from 300 to 400 feet wide had been effectively treated by one 

 trip of the plane and that the quantity of Paris green required was 

 at the rate of about 1 pound to 20 acres. This represented the 

 minimum quantity effective on water containing almost no debris 

 or aquatic growth. Under such conditions the writers' counts had 

 shown that 10 or more granules of Paris green per square inch usu- 

 ally gave 100 per cent mortality, whereas with a lower count some of 

 the larvse escaped. In these preliminary tests and in the next series 

 also a count of 10 granules per square inch was therefore taken as 

 the effective dosage, although it was found later that this quantity 

 was insufficient under natural breeding conditions where the larvse 



Fig. 2. — Dust cloud beginning to spread out among the trees following a trip of t.he 

 plane across Bunkum Woods 



are more protected by the debris and vegetation among which they 

 feed. 



The next tests were made in two patches of woods, to deter- 

 mine whether the dust could be forced to the ground through a 

 growth of leaves and brush. In the first of these the strip of woods 

 was fairly narrow, with only a moderately heavy growth of timber. 

 Two parallel lines of glass plates were placed on the ground under 

 the trees and the plane was flown at right angles to these lines, mak- 

 ing two or three trips across the woods at about the same place each 

 time (fig. 2). The mixture distributed consisted usually of 100 

 pounds of dust containing 10 pounds of Paris green. The lines of 

 glass plates, with 10 in each, were distributed across a strip 750 feet 

 wide. In the best one of the trials all of the plates showed the pres- 

 ence of Paris green, and all except two in one line had 10 or more 

 granules per square inch. 



