430 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 



tion. Now, the cottonwood is placed by botanists iu a genus diflfereut from that of 

 the willows, and the strangest thing about it is that the willows are not injured to 

 the same degree, even where growing in the neighborhood of the injured cotton- 

 wood. This is partly due, perhaps, to the tact that the willow does not suffer so much 

 from defoliation as does the cottonwood, though it is possible that a special cottonwood 

 feeding race of the species has been of late years developed in those sections where 

 the tree is so largely planted. This would be parallel to the well-known case of the 

 apple-maggot (Tri/peta pomonella), which, though infesting wild haws and crabs in 



Fig. 158. — Grub of streaked cottonwood beetle a, eggs, b, one enlarged; c, newly 

 hatched larva; , d d d, larviB of dififerent ages ; e, pupa, nat. size ; f, one of the 

 middle segments of the body of larva seen from above, showing tubercles, en- 

 larged. After Riley. 



all parts of the country, 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 iu the Eastern States is confined to willow and does not attack 

 the cottonwood. 



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

 cottonwoods begin to leaf out, the beetles pair, and the females begin laying their 

 «gg8 (fig. 158, a, h). These are placed upon the young leaves in dense masses of 

 from ten to a hundred eggs. Each egg is elongate-oval, pale yellowish-white in 

 color, rather soft, and about 0.5'""' long. The larva? (fig. 158, c, d) soon hatch and 

 develop very rapidly. At first they are black in color and gregarious iu habit, skel- 

 etonizing the leaf iu the immediate vicinity of the egg-shells. With the succeeding 

 molts the color becomes lighter and they separate, feeding upon leaves at some dis- 

 tance from their place of birth. These larvje, 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. 

 Ou attaining full growth they transform to pupae 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 insect is very rapid. Professor Snow states* that iu the 

 month of August only fifteen days are occupied from the hatching point to the issu- 

 ing of the adult. 



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



