Journal of Agricultural Research 
Vol. II, No. i 
18 
the young plants, although it is very partial also to some of the broad¬ 
leaved millets. On com it breeds continuously throughout the season. 
The writer found larvae in mines in corn leaves from May until severe 
frosts killed the plants in the fall. Next to young com the blotch miner 
apparently prefers the broad, hairy-leaved varieties of millet, such as Pan - 
icum miliaceum y although it has been reared from several varieties of the 
smooth-leaved millets. Occasionally it will be found in crab-grass (Pant- 
cum sanguinale ), and it breeds readily in barnyard grass (.Echinochloa 
crus-galli). It would not be at all surprising if in later years it should 
be reared from wheat and oats, as apparently the same kind of larval 
mine has been found in these plants, although the adults have not been 
obtained. 1 
CHARACTER OF INJURY 
In young com plants and in the small grasses and grains the larvae 
work from the tip of the leaf toward the base, devouring all of the tissue 
between the upper and lower epidermis (PI. I, figs. 2,3). The mandibles 
of the larva consist of two chitinized hooks, which are used in much the 
same manner as a hoe, portions of the thin layer of tissue being scraped 
from between the two surfaces of the leaf with every stroke. In small 
plants the larvae work the entire width of the leaf, leaving only the 
epidermis of the upper and lower surfaces. Plate I, figure 2, shows a 
young com leaf taken from a cage, with six larvae at work inside. Soon 
after the work is done the leaves have a colorless appearance, and in a 
few days they turn brown and curl up. One larva is sufficient to destroy 
a young com leaf, although as many as four have been found in a single 
leaf in the field, and as many as eight or ten have been found in a leaf 
in the rearing cages. Often there is not sufficient nourishment in a single 
leaf for the development of all when they are reared in confinement, in 
which case some perish. Sometimes in the field two or more leaves of a 
young com plant are attacked when the plant is only a few inches high 
and has, therefore, few leaves. It can be readily seen that com might 
suffer severely in a cold, backward season with this pest abundant. 
Instances have been noted where the tip of the mined leaf has been 
almost completely filled with water, although the larva may still be 
inside and apparently not seriously inconvenienced. Plate I, figure 3, 
shows such an instance, the epidermis of the upper and lower surfaces 
being separated for a distance of about one-fourth of an inch. The 
mines become filled in this way only when the weather is very rainy. In 
cases of this kind the larvae do not feed much until the water has evapo¬ 
rated, although under normal conditions they appear to feed continuously, 
the writer having observed them both night and day and never having 
seen them at rest for more than a few seconds at a time. 
1 It might be well to state in this connection that Asa Fitch (1856) reared and described a new species 
of Agromyza (A. tritici) from New York, c allin g it “the wheat mow fly.’* After reading the description 
in Fitch’s article and comparing it with the work of the miner at I*a Fayette, Ind., one readily sees that 
two species are involved. 
