4 BULLETIN 992, U. S. DEPARTMENT OE AGRICULTURE. 
beneath. Persian walnuts on the trees will often turn black from 
this cause during a period of only a few days. Quite often the first 
external evidence of the feeding of the larvae within a nut will be a 
slight seepage of dark juice from the oviposit ion wound, which will 
flow down and stain the skin of the nut (PI. IV, h). 
THE LARVA. 
The larva, or maggot (PI. II, <s, f; PL IV, <?), is white or creamy 
white, and is not stained by the dye-like, semiliquid matter in which 
it feeds. The dark-colored contents of the alimentary canal, how- 
ever, give to the immature maggots a brownish appearance. When 
full grown the}^ average 10 mm. in length by 2 mm. in width. The 
maggots are active and move about rapidly, using in locomotion their 
two anal hooks. They often remain in the walnut husk until severe 
freezing weather occurs, but take advantage of warm periods in the 
late autumn to leave the nuts and enter the ground a short distance 
for pupation. 
THE PUPA. 
The pupa (PL II, g, h) is formed by the shrinkage of the larva 
and is pale yellow, cylindrical, tapers slightly from the middle to- 
ward the ends, and is 5 mm. in length by 2.5 mm. in width. There 
are 11 plainly visible segments, the intersegmental grooves being 
shallow but distinct. Each end bears a pair of small, brownish 
tubercles and there is a rough, brown spot near one end where the 
larval head was retracted. In size, shape, and color the pupa re- 
sembles a grain of wheat (PL II, h). The pupae are formed in the 
ground, anywhere from half an inch to several inches beneath the 
surface, and the winter is passed in this stage. Most of the flies 
issue the following summer, but a few pupae hold over the second 
winter and the adults appear therefrom during the succeeding 
summer. 
THE ADULT. 
The adults of this insect vary considerably in size but average about 
7 mm. in length. With the exception of the eyes, heavy wing mark- 
ings, anterior margins of the abdominal segments, and bristle-like 
hairs, all of which are dark brown, the color is pale yellow. There 
is a lighter longitudinal line on each side of the thorax and the 
dorsal surface of the thorax is densely clothed with very short, 
yellowish hairs interspersed sparsely with long, stiff, dark-brown 
bristles. The head, sides, upper surface of the abdomen, and legs 
are covered more or less heavily with brown hairs. (PL III.) 
ACTIVITIES OF THE FLIES. 
The flies begin to issue from the ground at least as early as the 
middle of July in the latitude of West Virginia. In 1920 at French 
