338 



REPORT OF THE COMMISSIONER OF AGRICULTURE. 



has only taken to feeding on and injuring cultivated apples in some of 

 the New England States." 



This last conclusion is rendered all the more plausible from the fact 

 that, so far as known, the species in the Eastern States is confined to 

 Willow and does not attack the Cottonwood. 



NATURAL HISTORY. 



The perfect beetles winter in sheltered localities. In the spring, as 

 soon as the cotton woods begin to leaf out, the beetles pair, and the fe- 

 males begin laying their eggs ( Plate VIII, Fig. 1, a, b). These are placed 

 upon the young leaves in dense masses of from ten to a hundred eggs. 

 Bach egg is elongate-oval, pale yellowish-white in color, rather soft, and 

 about 0.5 mm long. The lame (Fig. 1, c, d) soon hatch and develop very 

 rapidly. At first they are black in color and gregarious in habit, skele- 

 tonizing the leaf in the immediate vicinity of the egg-shells. With the 

 succeeding molts the color becomes lighter and they separate, feeding 

 upon leaves at some distance from their place of birth. These larvas, 

 like those of other species of the genus, are peculiar for emitting from 

 the tips of the tuberculous spines, with which they are furnished, a 

 milky liquid, of a pungent, but not altogether disagreeable, odor. On 

 attaining full growth they transform to pupse upon the leaf, fastening 

 their hind legs to the leaf, and partially throwing off the last larval 

 skin. The perfect beetles issue soon after. There are at least three 

 annual generations, and probably more, as the development of the in- 

 sect is very rapid. Professor Snow states* that in the month of Au- 

 gust only fifteen days are occupied from the hatching point to the issu- 

 ing of the adult. 



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 exception 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 susceptible to any of the trapping remedies which are used 

 against the quite closely allied Elm-leaf beetle (Galeruca ocanthomelcena)^ 

 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 experiments made with 

 the arsenical poisons, Loudon 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 effica- 

 cious in destroying the beetle, London 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 re- 

 lating 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 Laving 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 divided, and 

 will diffuse in the water without appearing in lumps. The Hour is a suitable medium 

 to make the poison adhesive. Tlie London purple is then placed upon the gauze and 

 w aahed in by the remainder of the water, until the barrel is filled. In other tests, the 

 Hour was mixed dry with the poison powder, and both were afterward washed through 



* Observer of Nature, Lawrence, Kans., November 23, 1875. 



