THE COTTONWOOD LEAF-BEETLE. 431 
Remedies. — According to all reports, but little is to be expected from the natural 
enemies of this species, for birds do not seem to touch it, and, with the single excep- 
tion of the larvae of lady-birds, we have neither found nor heard of any other insect 
enemies. 
Inasmuch as it undergoes all of its transformations upon the leaves it is not sus- 
ceptible to any of the trapping remedies which are used against the quite closely 
allied elm-leaf beetle (Galeruca xanthome! a>na), which was treated of in our last 
annual report (pp. 159-170), and the larva of which descends to the ground to enter 
the pupa state. In that article, however, we gave in detail the results of experi- 
ments made with the arsenical poisons, London purple and Paris green, and these 
results may be applied with certainty to the case of the cottonwood leaf-beetle under 
consideration. Premising with the fact that while equally efficacious in destroying 
the beetle, Loudon purple seems to injure the tree less than Paris green, we repeat, 
for the benefit of the Western reader who may not have access to the report of 1883, 
the two paragraphs relating to the preparation of the poison and the effects of the 
mixture: 
"Preparation of the poison. — London purple (one-half pound), flour (3 quarts), and 
water (barrel, 40 gallons) were mixed, as follows: A large galvanized iron funnel of 
thirteen quarts capacity, and having a cross-septum of fine wire gauze such as is used 
for sieves, also having vertical sides, and a rim to keep it from rocking on the barrel, 
was used. About three quarts of cheap flour were placed in the funnel and washed 
through the wire gauze by water poured in. The flour in passing through is finely di- 
vided, and will diffuse in the water without appearing in lumps. The flour is a suitable 
medium to make the poison adhesive. The London purple is then placed upon the 
gauze and washed in by the remainder of the water, until the barrel is filled. In other 
tests, the flour was mixed dry with the poison powder, and both were afterward washed 
through together with good results. It is thought that by mixing in this way less flour 
will suffice. Three-eighths of a pound of London purple to one barrel of water may be 
taken as a suitable percentage. Three-eighths of an ounce may be used as an equiva- 
lent in one bucketful of water. The amount of this poison was reduced to one-fonrth 
of a pound to the barrel with good effect, but this seems to be the minimum quantity, 
and to be of value it must be applied in favorable weather and with unusual thor- 
oughness. With one-half or three-fourths of a pound to the barrel, about the max- 
imum strength allowable is attained, and this should be applied only as an extremely 
fine mist, without drenching the foliage. 
"Effects of the mixture. — The flour seems to keep the poison from taking effect on 
the leaf, preventing to some extent the corrosive injury which otherwise obtains 
when the poison is coarsely sprinkled or too strong. It also renders the poison more 
permanent. On the leaves, especially on the uuder surfaces, the London purple and 
flour can be seen for several weeks after it has been applied, and the insect is not 
only destroyed, but is prevented from re-appearing, at least for a long period. By 
poisoning again, a few weeks later, the insect is deterred with greater certainty for 
the entire season. By being careful to administer the poison before the insect has 
worked, and, above all, to diffuse the spray finely but not in large drops, no harm 
worth mentioning will accrue to the plant from the proportion of poison recommended. 
The new growth, that developed after the first poisoning, was protected by one-fourth 
of a pound to the barrel in 1882. From midsummer until autumn the unpoisoned 
half of the grove remained denuded of foliage, while the poisoned half retained its 
verdure. The little damage then appearing in the protected part was mostly done 
before the first treatment. Eggs were laid abundantly throughout the season. Many 
of these seemed unhealthy and failed to develop, probably because they were poi- 
soned. Many hatched, but the youug larvae soon died. The eggs were seldom 
deposited on the young leaves that were appearing after the poison was applied, 
but were attached to the developed leaves, and here the larvae generally got the poi- 
son to prevent their attack upon the aftergrowth. Still the young leaves became 
