THE ALFALFA CATERPILLAR. 3 
method of dealing with the pest. As no remedy was known, plans 
were at once begun for investigating the outbreak and if possible 
working out some plans of controlling the same. 
This circular is a partial report of the work done by the writer in 
the Imperial Valley the past season (1910), and while the investi- 
gation is still under way, another year being necessary to complete the 
same, it is thought desirable to give to the farmers in the alfalfa- 
growing section of the country the information secured, it being of 
such a nature as to be of great immediate benefit, if put to. practical 
use, in controlling the pest. 
DISTRIBUTION. 
According to Scudder, this species is more especially a western 
insect, being, as a rule, much more abundant west of the Mississippi 
River than east of it, and although its range extends eastward it is 
rather rarely found east of the Allegheny Mountains. In the West it 
occurs from Mexico northward into the Dominion of Canada, thus 
covering the chief alfalfa-growing section of the United States. It is 
especially abundant throughout the regions where irrigation is most 
extensively followed. 
DESCRIPTION OF THE SPECIES. 
A meager description is given here of the various stages of develop- 
ment, in order to enable the casual observer to recognize the different 
forms: 
The adult (figs. 2, 3).—The wings of the adults vary in color from 
yellow to white, being usually a sulphur-yellow above, with black 
outer margins, a conspicuous black spot in the center of each fore 
wing, and a faint yellowish spot in the center of each 
hind wing. The underside of the wings is of a lighter 
shade than the upper surface and is the side noticed 
when the butterfly is at rest with its wings folded 
above its back. The wing expanse is nearly 2 inches; 
in some it is a little less than this and in a few a 
little more. 
The egg—The eggs (fig. 4) are small, only 0.06 Fis-4.—The alfalfa 
- : : - ~ eaterpiliar: Egg. 
inch long, with from 18 to 20 slightly raised longitu- —_ Greatly enlarged. 
dinal ridges or ribs, broken by cross lines. They are  (Redrawn from 
elongated, white when laid, but turning reddish ah 
brown after the second day, and are deposited upright, with the 
basal end attached usually to the upper surface of the leaf. They 
are always deposited on fresh, green alfalfa, and never on dry or 
partially matured alfalfa. 
The larva—tThe full-grown larva (fig. 1) is usually 1 inch long, 
sometimes a little over, dark green in color, with a white stripe on 
(Cir. 133] 
