4 BULLETIN 992, U. S. DEPARTMENT OF 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 oviposition wound, which will 

 flow down and stain the skin of the nut (PL IV, l>). 



THE LARVA. 



The larva, or maggot (PL II, e, f; PL IV, c), 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 they 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 larval head was retracted.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 



