350 Bulletin No. 112. [January, 



that practically all these may be killed by dipping the infested 

 leaves in dilute emulsions (those used varying in content from 2j4 

 to lo 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 tinder 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 



paler and often discolored, and fsiauy more or less dr^^^^^^^ ""^ "°* ""''^ motionless but 



