Apr. 15, 1914 
Corn-Leaf Blotch Miner 
19 
The leaves of the grasses and smaller grains are affected in the same 
manner as the leaves of young corn, but as they are much smaller they 
can not accommodate so many larvae. This miner is not able to go down 
the base of one leaf and up into another as is Ceradontha dorsalis Toew; 
therefore it has to depend entirely upon the nourishment to be derived 
from one leaf. C. dorsalis makes a long, narrow mine, working toward 
the base of the leaf, and in small plants it may go down the leaf sheath 
and work out into another leaf. 
From the time com leaves are an inch or more in diameter until they 
are mature the larvae have plenty of room for 
development. The mines take on a different 
character in large leaves. In these they may 
start at any point along the leaf. Sometimes 
several larvae will hatch in close proximity, 
and the mines will coalesce, forming a large 
blotch, which may be several inches in length 
and nearly an inch across. A mine like this is 
shown in Plate I, figures 5 and 6. At a distance 
of 10 or 15 yards such mines show up very dis¬ 
tinctly against the dark-green background as 
large grayish or whitish blotches. Where there 
is only one larva to a mine in these large leaves 
the mine may be a comparatively long, narrow 
one (3 to 4 inches in length), gradually enlarg¬ 
ing, the last third to half forming a blotch. In 
other instances the mine may be 3 inches in 
length and about three-eighths of an inch across 
for nearly the entire length, ending in a blotch 
about one-half inch in diameter, as shown in 
Plate I, figure 7. The mines may, however, 
form blotches, as shown in Plate I, figure 1. 
When the plants become older and tougher, 
the miners do not devour all of the tissue be¬ 
tween the two leaf surfaces. In this case a 
miner that is working in the underside of the 
leaf would scarcely be noticed from the upper 
surface. Therefore, the greatest injury is 
wrought when the plants are young. If very 
abundant, however, the larvae could cause serious injury to corn in 
advanced stages of growth, provided their parasitic enemies were not 
present in sufficient numbers to hold them in check. 
Fig. 2 .—Tip of corn leaf, showing 
work of A gromyza parvicornis , 
the com-leaf blotch miner: o, 
Egg, greatly enlarged; 5 , newly 
hatched larva in mine; c, feeding 
punctures of adults. Much en¬ 
larged. (Original.) 
DESCRIPTION OF AGROMYZA PARVICORNIS 
THE EGG (FIG. 2, a) 
The egg is milky white and flattened from above and below. It is from 0.4521 to 
0.5043 mm. in length and from 0.1739 to 0.1913 mm. in width. It is broadly rounded 
at each extremity and slightly constricted at the center. The anterior extremity is 
slightly more pointed and somewhat more flattened. The surface of the chorion is 
smooth and apparently without any markings whatever. 
