12 
BULLETIN 116. 
the insect has not often been a serious pest in any one locality long 
enough for the problem to be worked out. 
Summer Treatment. —In 1884 Dr. Forbes made a number of pre¬ 
liminary laboratory experiments on the effect of insecticides on young 
lice. A leaf dipped in per cent kerosene emulsion showed that the 
lice were killed. A branch treated in the same way showed a mortal¬ 
ity of three-fourths in twenty-four hours. A branch sprayed with the 
same preparation showed one-half dead after four days. A branch 
dipped in five per cent solution killed all. Whale oil soap appeared to 
be less satisfactory for the larvae were not all killed with a solution 
weaker than one pound to two gallons, and these strengths all did 
greater or less injury to the foliage. 
In the summer of 1904, Mr. H. E. Weed did considerable spraying 
in the parks of Chicago. The work began in the middle of July and 
extended to the first of September. Kerosene emulsion of eight or ten 
per cent strength was used at first, but afterward increased until fifteen 
per cent was reached. The results I give in his own words: 
‘Practically none of the insects were killed with either the eight or ten percent 
emulsions. An examination at Prof. Forbes’ office of leaves sprayed with 12% per¬ 
cent some days after showed that something over fifty per cent were killed but the 
death of some of these was doubtless due to natural causes. The fifteen per cent 
emulsion killed the greater portion of the Pulvinaria , but as this strength took 
practically all of the leaves off the boxelder, all from the lindens and fully one-half 
from the maples, the remedy was at least equal to the disease.” 
The failure of these later treatments compared with those of Dr. 
Forbes is doubtless due to the age of the young scales. It is probable 
that the greater portionof the young larvae were protected by waxy ex¬ 
cretions of considerable thickness by the middle of July. From ex¬ 
periments which are described below I am convinced that the newly 
hatched larvae are very easily killed. Kerosene emulsion as low as 
five per cent and Good’s whale oil soap as weak as one pound to four 
gallons appeared to be entirely effective. 
From the foregoing it must appear that a summer spray for the 
young scales alone must be a very protracted and expensive task. It 
is probable that a weak spray will not be effective on a scale more than 
a week or ten days old. The greater portion of the eggs hatch probably 
between the middle of June and the first of August. Thiswould neces¬ 
sitate from four to six very thorough treatments to greatly reduce the 
numbers, even granting that all of the lice may be reached by each 
spray, a condition which anyone who has had very much practical ex¬ 
perience would hesitate to admit. 
In the summer of 1904, the writer made a number of preliminary 
experiments for the purpose of pointing the way to a summer treat¬ 
ment. Since these have not been published before they are given in 
full. The first eleven were treated on July 3, and the others on July 5. 
The examinations were all made on July 14, and eggs which appeared 
to be alive in Nos. 4, 5, 10, and 16 were isolated and examined July 26. 
TABULATED STATEMENT OF TESTS WITH INSECTICIDES 
EXP. CONDITIONS. INSECTICIDE RESULTS 
1 Large scale full of unhatched Ker. Emul. 50% Everything soaked 
eggs. Some larvae kerosene with oil and dead, 
running about. 
