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JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
secure a satisfactory distribution of the powder and just as low as 
possible, perhaps averaging not more than 20 feet above the crowns of 
the taller trees. Although plans were made to secure the precise time 
taken in the liberation of the dust by stationing observers in different 
parts of the woodland, it was found impossible to do this accurately 
since the observers could not always see just when the hopper was 
opened and closed. 
No dust was applied during the afternoon of May 24. In the early 
evening of that day, l 1 /^ hours after the last hopperful of poison had 
been distributed and before the lead had had a chance to ‘‘set” by dew, 
a violent rainstorm almost of the dimensions of a cloudburst occurred. 
The following morning intermittent showers fell until about 11 o’clock 
when the weather cleared and an additional 100 lbs. of the powder was 
applied to a section of the woods. 
Behavior of the Dust When Released 
The influence of the “slip stream” persisted some seconds after the 
dust was released and the white trail floated out behind the moving 
plane. Presently, however, this was lost and the wind floated the dust 
cloud over and through the trees. One of the most gratifying phases of 
the behavior of the dust was its power of penetration or what may be 
termed its “covering power.” After the dust cloud was liberated over 
the woodland it gradually settled through the crowns of the trees or the 
upper canopy of foliage, and for a period of four minutes after the passage 
of the plane we were able to detect floating particles of it. 
As a result of this comparatively long period, most excellent dis¬ 
tribution was effected. Not only were the tree tops well covered, but 
the leaves of the underbrush as well. Even the leaves of plants growing 
under the double canopy of tree tops and underbrush were well covered, 
and it is the writer’s belief that the distribution of the poison excelled 
that which might have been obtained by the use of liquid sprays. 
Effect of the Poison on the Caterpillars 
Following the dusting of May 24, when it will be recalled the work 
was discontinued at noon and a heavy rain fell 7M hours later, a large 
sheet 9 x 9 ft. was placed near an elm badly infested with the larvae. 
The caterpillars thus had but a few hours of feeding before the storm. 
The following morning we found 109 caterpillars on the sheet, many of 
which were dead but some still showed signs of life. The latter, 19 in 
