include a number of small flies, under one-sixth of an inch long, with
spherical head, rounded greenish eyes, strongly arched thorax, and short
egg-shaped abdomen, pointed in the male and blunt in the female. The
headless larvæ live in the haulms of grasses and species of grain; the
life history of a few forms only is adequately known. A few are harmful,
especially as there are two or three generations annually. The late
summer generation often appears in large numbers, indeed in actual
swarms. Since no species lives exclusively on corn, it is impossible to
keep them down for a long period of time. I describe only two species:—
[Illustration:
FIG. 117.—The Ribbon-footed Corn Fly (_Chlorops tæniopus_).
]
The =Ribbon-footed Corn Fly= or =Yellow Haulm Fly= (_Chlorops
tæniopus_), nearly one-sixth of an inch long, shining yellow; the
antennæ are black, and there are three longitudinal stripes on the
dorsal side of the thorax and four transverse bands on the abdomen of
the same colour; the latter region is scarcely longer than the thorax.
The insect (Fig. 117) is on the wing in cornfields about the middle of
May. It lays its eggs separately on the upper leaves of various species
of wheat, rye, and barley, choosing the upper side of the blade, not far
from the sheath. Only those plants are selected for the purpose in which
the ears are still hidden deep down between the leaf-sheaths. Wheat
plants are picked out whenever possible. The maggot when hatched works
its way between leaf-sheath and haulm, digging into the latter. It is
yellowish white, clear and translucent, and about a quarter of an inch
long. While still young it penetrates the haulm, and then attacks the
developing ear or the upper part of the haulm which immediately adjoins
this, and travels gradually up to the first node of the haulm or nearly
so, always continuing to slowly suck. Thus a furrow, from 2½ to 3½
inches long (Fig. 118, C and D), is formed along the surface of the
upper part of the haulm, and often also along the lower part of the ear.
The part of the haulm attacked swells transversely, and the part below
often remains short, so that the ear cannot emerge from the leaf-sheath;
but, in any case, only small worthless grains are developed. The furrow
is always much deeper below than above, and its margins thicken in
consequence of the swelling of the tissues of the haulm. At the end of
June or in July, the larva becomes a pupa at the lower end of the
furrow. The yellowish-brown pupa (Fig. 118, B), one-fifth of an inch
long, remains as such in the furrow for three weeks; the fly emerges in
August. Very considerable damage may be done by the first generation, of
which the habits have just been described. During 1869 in Silesia, from
two-thirds to five-sixths of the ears in many fields remained hidden in
the leaf-sheaths, and consequently gave no increase. The first
generation of the ribbon-footed corn fly can also develop in the way
described in the haulms of several grasses, _e.g._ in species of _Poa_
and _Holcus_.
The flies, emerging in late summer, lay their eggs, here, too,
separately, on the leaves of grass or corn. Wherever possible, they seek
out for the purpose the winter wheat plants then present in the fields,
but also content themselves with rye, or even with wild or meadow
grasses; they have to be satisfied with grasses if, at the time of
egg-laying, the winter corn is not yet up. The maggot, when hatched,
works its way to the inner side of the leaf-sheath, and thence to the
apex of the still very small haulm; there it remains during the winter.
The damage becomes apparent the following spring. The growth in length
of the haulm in question is extremely small, while growth in thickness
increases to an abnormal extent. Almost all the leaves completely
surround the haulm, which swells to an enormous extent (Fig. 119),
together with the enclosing leaf-sheaths, which are much broader than
usual. The unattacked plants are naturally much larger than the sickly
ones, and deprive these of air and light, so that they die down, being
overshadowed, not only by the sound haulms, but also by their own
secondary shoots. The resulting damage may be tolerably great,
especially at the edges of the field. It may happen that both summer and
winter generations of the ribbon-footed corn fly are harmful in the same
district; but it frequently happens that only one or the other is
complained of in a particular spot. It is only natural that the flies,
which swarm around in May, and again in August, September, or October,
should not always find suitable corn plants upon which to deposit their
eggs. In such cases grasses are used. _Remedies_: Sowing the summer corn
as early as possible, that it may be developed to a stage which is
unsuitable for the purpose of egg-laying, before the flies appear. The
winter seed, however, must be sown as late as possible, so that the
second generation of flies may find no corn plants fit to lay their eggs
upon. Bearded wheat, especially the strongest varieties, should be sown
in preference to awnless wheat. Careful tillage and suitable manuring,
so that strong plants of rapid growth may be produced.
[Illustration:
FIG. 118.—The Ribbon-footed Corn Fly (_Chlorops tæniopus_); larva (A)
and pupa (B) magnified. To the left a wheat haulm and ear (C) with
the furrow (_q_) dug out by the larva; the pupa (_p_) is seen at the
bottom of the furrow. To the right a wheat haulm with furrow (D) and
the larva (_r_) lying in it.
]
[Illustration:
FIG. 119.—A wheat plant distorted by
the winter generation of the Ribbon-footed
Corn Fly.
]