THE COTTONWOOD LEAF-BEETLE. 431 



Eemedies. — 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 larv;e 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 xanthomeUvna), 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 cottouwood 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: 



i^ Preparation of the poison. — Loudon 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 fiue 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 au ounce may be used as an equiva- 

 lent in one bucketful of water. The amount of this poison was reduced to one-fourth 

 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. — Tha flour seems to keep the poison from taking effect on 

 the leaf, preventing to some extent the corrosive injury which otherwise obtains 

 when the jjoison is coarsely sprinkled or too strong. It also renders the poison more 

 permanent. On the leaves, especially on the under surfaces, the Loudon 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 uupoisoned 

 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 young larvte 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 larvie generally got the poi- 

 son to prevent their attack upon the aftergrowth. Still the young leaves became 



