76 
Journal of Agricultural Research 
Vol. I, No. i 
Mr. McGregor’s notes are as follows: 
Data have not been accumulated from which to compute the percentage of leaves 
affected. It is quite evident, however, that at this season the plants outgrow the 
infestation and the rapidly forming leaves tend to reduce the percentage of infested 
leaves. This phenomenon easily leads to the erroneous inference that the pest prefers 
the seedling leaves and becomes less troublesome as the plants develop. On the 
contrary, later on in the season freshly formed leaves appear to be just as desirable to 
the leaf-miner as did the seedling leaves. The tortuous courses of the burrows often 
sever the main veins of the leaves, causing the death of more or less of the leaf, which 
may harbor several individuals. 
The habits of the leaf-miner, as observed in cotton leaves by Mr. 
McGregor, are here quoted: 
The duration of the larval stage, while not fully established, approximates a week. 
Feeding takes place and the tunnel is formed in the palisade tissue nearer the upper 
surface * * *, as the grub increases in size the caliber of the burrow expands until 
full development is attained at its cavernous end, when the larva escapes through a 
valvelike incision and pupates in the soil. In the laboratory adults issued six days 
after pupation. 
Three hymenopterous parasites were reared by Mr. Rutherford from 
the pupae of the host. 
NATURAL ENEMIES OF THE SERPENTINE LEAF-MINER 
Throughout its entire area of distribution this insect is severely para¬ 
sitized. Excessive parasitism was noted in the earliest studies of the 
species about Washington, D. C., and the senior author reared numerous 
parasites from the larvae mining in the leaves of white clover at Oxford, 
Ind., in 1884. In connection with the studies made during the last 
three years there have been reared at least 28 species of hymenopterous 
parasites from the mines of this insect in the foliage of alfalfa and other 
forage crops in the United States. At times these minute enemies have 
become so numerous as to render even a careful study of the pest itself a 
matter of some difficulty. But for their presence these leaf-miners would 
beyond a doubt work much more serious ravages in the alfalfa fields of 
the West than they do at present. Indeed, one is inclined to wonder 
what the actual financial effects would be were some condition to arise 
suddenly whereby the numbers and efficiency of these natural checks 
were radically diminished. 
The first generation of the leaf-miner to appear in the spring is not 
severely parasitized, and from larvae and puparia collected at this time 
numerous flies usually emerge. The following generation is more severely 
parasitized, and thereafter the parasites increase rapidly, infestation becom¬ 
ing more and more severe, so that mined alfalfa leaves collected during 
the summer and fall will usually yield parasites instead of adult leaf- 
miners. To illustrate this point, the junior author, near Salt Lake City, 
Utah, on September 16, 1911, selected in the field 45 mined alfalfa leaves, 
43 of which contained 1 mine each, while 2 had 2 mines. Of the 47 mines. 
