15 
with the arsenicals, even if used at a strength sufficient to burn the 
foliage, would support .these caterpillars without destroying more than 
a small proportion of them. 
Efforts were therefore made to discover an arsenical compound which 
could be applied to trees at a strength considerably greater without 
burning the leaves. These efforts were successful, and the substance 
known as arsenate of lead was developed and is coming into general 
use, not only against the Gipsy Moth, but against other leaf-feeding 
insects. This substance may be sprayed upon the tenderest foliage at 
a dilution of 10 pounds to 100 gallons of water without injury, whereas 
1 pound of paris green to 100 gallons of water frequently injures the 
leaves. Even with this valuable arsenical combination (the discovery 
of which, it must parenthetically be stated, has already proved of the 
greatest value to the economic entomologist) it was found that except 
under certain conditions spraying could not be generally adopted with 
perfect effect against the Gipsy Moth. A certain proportion of the 
caterpillars on sprayed trees always escaped, so that it can not be abso- 
lutely relied upon for exterminative work. 
Moreover, extensive experimental work has shown that there is only 
about one month in the year during which effective spraying can be 
done. This is from about the 15th of May. when most of the caterpil- 
lars have hatched, to the loth of June, when ail have hatched, and 
when most of them have reached the age when they will cluster under 
the burlap. If, during this short period, there are two or three weeks 
of rainy weather, as is frequently the case, very little effective spraying 
can be done. Furthermore, a concentration of the work in this short 
season makes necessary a great expenditure for spraying apparatus, 
and necessitates the employment of a large force of men tor this pur 
pose — a difficult matter, since proper spraying requires expert hands. 
The conditions under which spraying is still carried on and undei 
which it is the only practicable remedy, are such as exist in certain 
parks — franklin Park, for example, where there are extensive stretches 
of tangled vines and valuable shrubbery which hide the egg masses 
and which can not be banded, and which, at the same time, on account 
of their value, can not be burned over. Here spraying is still carried 
on, and with good effect, owing to repeated operations and great per- 
sistence, which, of course, involve a very considerable expense. 
Different methods of egg destruction have been tried. The first 
recommended was to the effect that the eggs be scraped from the I 
and burned. They were scraped off or cut away from the trunks on 
which they rested, placed in tin cans, and burned in stoves or brush 
tires. A tierce heat is required for their destruction. Whenever the 
eggs were very numerous in undergrowth or waste land, tire was run 
over the dead leaves and debris as an experiment, but this method 
seemed to have but little effect, as the heat was not sufficiently intense. 
The hairy cover seems remarkably noncouductix e and renders the 
