20 BULLETIN 438, U. S. DEPARTMENT OF AGRICULTURE. 
To ascertain how far the control of the pear pests just mentioned 
could be relied upon to keep the pear leaf-worm in check, control 
experiments were made in the spring of 1913 in California and in 
1915 in the State of Washington, and are shown in Table XVI. 
Actual count was made 24 hours after spraying, and the larvee 
found on the leaves only were taken into consideration. Leaves 
with-holes eaten in them, but with no larve present, were not made 
part of the record. This spray was applied with pressure, the force 
of which, when hitting the leaves at close range, more than likely 
caused larvee to loosen their hold and fall to the ground. It is also 
more than probable that some sick larve likewise fell before the 
count was made. At that time leaves were noticed with holes in 
them smaller than those which would have been produced by larvee 
remaining on the leaf until their full development had been attained. 
The mortality therefore would be greater than is recorded in these 
tables, and this accounts in a measure for the difference in the results 
found for the same formula applied in California and in the State of 
Washington, because in the latter instance the experiment was made 
under laboratory conditions which would afford opportunity for closer 
observations and would yield more precise results. 
Field conditions prevailed in the California experiments, because 
common every-day spraying, as ordinarily practiced in orchards for 
other pests, was the only object in view as a control at the same 
time for the pear leaf-worm. 
In the control table (Table XVI) the experiments with tree No. 3 
and tree No. 7, in which a contact spray was used containing 
fish-oil soap and extract of nicotine, indicate a comparatively small 
percentage of mortality compared to that in which the material con- 
tained in addition arsenate of lead, as in the experiment with tree 
No. 2. But it must be mentioned that in the case both of tree No. 
3 and of tree No. 7, the absence of larve on leaves with holes when 
the count was taken was very conspicuous and the larve that sur- 
vived were all large. ; 
A contact spray, whether with or without the addition of dis- 
tillate oil, is a mechanical emulsion or mixture, which, to be effective, 
requires application with greater pressure than does a poison spray. 
Because of this, the liquid strikes the leaves with enough force to 
dislodge many of the worms, which drop to the ground, where death 
ensues, caused by the spray adhering to them. , 
The addition of fish-oil soap to a mixture of water and nicotine 
extract increases the efficiency of the spray by imparting to the 
liquid more penetration and better spreading and adhering properties. 
