107 
that practically all these may be killed by dipping the infested 
leaves in dilute emulsions (those used varying in content from 2^ 
to 10 per cent, of kerosene), unless the application be delayed too 
long after hatching. When the young are a week or two old they 
are partially protected by a waxy covering against the action of the 
oil. The test of death used was a thoroughly reliable one. The 
young were at this time so small and transparent that the action of 
the heart could be readily seen under a microscope, and the cessation 
of this action was the mark of death depended upon. As the maple 
scale disappeared from my neighborhood in 1885, no further experi- 
ments were made at that time. 
In 1904 the Commissioners of the North Shore Park District, 
above Chicago, of which Robert W. Vasey was president, engaged 
Mr. H. E. Weed, of Chicago, to treat one hundred and twenty soft 
maples and box-elder trees in their charge, along the boulevards, for 
the destruction of the cottony maple scale. A report of this treat- 
ment by Mr. Weed was printed in Bull. 52 of the U. S. Bureau of 
Entomology. The results of his work were submitted to me for 
examination in August and September, 1904, by Mr. Vasey, who 
sent me leaves from the trees which had been treated with a 12 per 
cent, emulsion. 
The scale insects on these leaves were carefully examined at 
my office by Mr. Hart, who found that out of 1781 scales 610 were 
alive and 1171 were dead.* Practically all the living scales were on 
the under surface of the leaves, only i per cent, of those on the upper 
surface being still alive. The ratio of the dead to the living on these 
leaves was 60 per cent. ; but as it seemed likely that some scales were 
dead before the spray was applied, Mr. Vasey sent me, for com- 
parison, at my request, leaves from infested trees not treated. An 
examination of these untreated leaves showed that 22 per cent, of 
those on the upper surface were dead and 4 per cent, of those on the 
lower surface. Making the necessary correction, it was found that 
57 per cent, of the scales alive when the trees were sprayed had been 
killed by the treatment. The spray thus tested was applied Au- 
gust 29. 
According to Mr. Vasey, the insects had hatched very slowly 
that year, owing to the backward season, but had been in condition 
for treatment with the kerosene spray for some three or four 
weeks preceding. It will be seen, consequently, that the treatment 
was too late to produce the full effect upon the young. Further 
••The 3'ouug' insects were by this time so opaque that the moveiiieiits of the heart could 
no long-er be seen; but it was found that living- individuals, when displaced and inverted, 
made slow movements of the leg's, and that dead individuals were not only motionless but 
paler and often discolored, and usually more or less dried up. 
