VOL. III.] Leaf-Miner. 235 



Leaves containin.^ larvee were collected on May 4 of the same 

 year, and put in a jar with earth to breed, but the larvae all seem- 

 ingly shriveled up and became hard and dried. At this date more 

 than two-thirds of the larvae had left the leaves. 



The spring of the present year the leaves of the Cottonwood had 

 been out not more than one week when it was found, April 21, 

 1892, that they contained good-sized larvae of this miner. It would 

 therefore seem that the eggs must be deposited in the leaf-buds be- 

 fore the leaves appear, perhaps about the time the buds begin to 

 swell. 



On April 25 of this year, most of the larvae were apparently full- 

 grown, and accordingly a good number of small branches bearing 

 leaves filled with healthy larvae were put in a breeding cage, the 

 branches being inserted in a receptacle which was kept filled with 

 water. The leaves remained green and healthy for days, until all 

 the larvae had disappeared. The next day, April 26, a large num- 

 ber of the larvae had already left the leaves, and were crawling on 

 the earth in the bottom of the cage. They seemed to manifest a 

 migratory instinct, and did not appear incHned to bury themselves 

 at once in the soil. The migratory larva seems to lose the blackish 

 dots on the anterior segments both above and below, and is entirely 

 of a whitish color and somewhat shorter than before. Two or three 

 of them were noticed going into the earth, but they were subse- 

 quently found perfectly hard and dried, and this was likewise the 

 fate of all the others, which shriveled up and died on top of the earth 

 within a day or two. They would not crawl under chips which 

 were placed within the cage. All natural conditions had been care- 

 fully studied and provided, but to no avail. On April 29, the larvae 

 had all left the leaves in the breeding cage. Some very small larvae 

 were at work on April 25, along with the apparently full-grown 

 ones. 



Five of these miners were often found in one leaf this season, but 

 the leaves of the trees were not so totally destroyed as in 1891. In 

 one case even seven larvae were found in the sam.e leaf. They all 

 begin separately, and work till their mines meet. The two skins 

 of the leaves then become filled with the very fine black frass or ex- 

 crement of the larvae. They feed by day, and. so far as observed 

 always with the venter toward the upper surface of the leaf. They 

 leave the leaf by making an incision in the upper skin just in the 



