INSECTS (ANIMAL BLIGHTS) AFFECTING CORN CROPS.
The different families and species of insects affecting the various
kinds of corn crops in all their stages of growth are so numerous, that
a detailed list of them would occupy greater space than we can devote to
this chapter.
In this position of affairs we have thought it wise to confine our
remarks to some of the commoner and more mischievous species, choosing
those more particularly which are common to the wheat crop, of which the
following may be at once introduced as a summary in itself sufficient to
show what the farmer may expect at each stage of growth:—
1. { The _Slug_, } Attacking the plants soon after germination.
{ The _Wire-worm_, }
2. { The _Gout Fly_, } That attacks the wheat stems as they begin to
{ The _Saw Fly_, } form.
3. The _Wheat Midge_—Commencing their injuries in the young flower.
4. The _Aphis Flea_—Which attacks the _rachis_ and floral envelopes.
5. { The _Ear cockle_, } Which destroys the growing grain.
{ The _Corn Moth_, }
6. The _Corn Weevil_—Which eats the flower from the grain.
7. The _Little-grain Moth_—Which attacks the grain in store.
8. The _Meal-worm Beetle_—Living upon ground corn or flour.
Now, this list may be said to have reference to eight stages in the
growth and preparation of wheat, and they mostly apply to other grains
also—namely, 1. The germinating plant; 2. The growing plant; 3. The
growing flower; 4. The green ear of corn; 5. The young grain; 6. The
perfected grain; 7. The stored grain; and 8. In the state of flour.
1. The _Slug_ may be described as a houseless snail. There are several
species, but the milky slug (_Limax agrestis_) and the black slug (_L.
ater_) are those most common to our corn crops, and are more especially
mischievous to wheat; for, as this crop usually succeeds clover or
“seeds,” in which they breed most rapidly, so, the older the clover lea,
the more eggs will be ready to hatch in the wheat crop, and this all the
more readily as the wheat is nearly always put in with a single
ploughing, and with as little cultivation as possible.
The best remedy will be found in encouraging insectivorous birds—the
lark, rook, starling, peewit, and others, eating them either in the egg
or young state with great avidity; a good assistance to whose labours
may be supplied in a few broods of ducks from the farmyard, which it
will pay well to have tended by a good boy—where such can be found—as
these birds are most efficient as destroyers of slugs and caterpillars.
Store pigs turned into old leas, where they can do no mischief, will get
no bad living where snails and insects abound.
_Wire-worms._—The several species of beetle which produce the wire-worm
belong to the genus _Elater_. They are of a long oval shape: about half
the length belongs to the head and thorax, and the other to the abdomen.
Every schoolboy knows that when he holds the insect on its back it
elevates the abdominal portion, and again lets it fall so as to make a
beating sound; and hence its generic name, and also its common name of
click-and-hammer beetle. If he remove his finger when in this position,
the creature immediately skips up and turns on its feet, from which
action it has got the name of “skipjack.”
Curtis has estimated nearly seventy species of click-beetles as
producing wire-worms in this country; but the three following are those
generally met with—_Elater lineatus_, _E. obscurus_, and _E.
ruficaudis_. These all attack corn and almost every other kind of
vegetable.
The larvæ of these are very much alike, being hard, leathery, wiry
caterpillars, which vary in length to about three-quarters of an inch,
according to age. These are mostly smooth, and have six feet on their
thoracic segments, and a false foot or _proleg_ in the middle of the
underpart of the terminal section of the abdomen—characters by which
wire-worms may be distinguished from all others. Their length varies
with age; as they live for some years in the larva state, so the
different sizes mark so many broods, which in some fields are annually
provided for. It should here be observed that the wire-worm does not
breed; these larvæ can only be hatched from the eggs of the female
click-beetle: hence, then, destroying the worms prevents the development
of their parent.
Now, as we have seen whole fields of wheat destroyed by wire-worms, it
becomes important to examine the nature of this attack, with a view to
point out a remedy. If, then, we go into a corn field in early spring,
and see the young wheat blades looking yellow and sickly, we shall
seldom be long in finding the wire-worm, on carefully taking up some of
the affected plants. Its position will be at the base of the plant,
sometimes eating its way into its centre, and so eating out its very
heart; or perhaps it may nibble away the outer coat of the young stem,
and so prevent any nutriment passing into the blade. One worm will be
enough to kill a single blade; but, alas! it frequently happens that he
either visits all the blades, or is assisted by many individuals to each
plant. This abundance we have observed more particularly on the breaking
up of old pastures, old seeds, or saintfoin _lea_, in which not only
have we many broods of wire-worms, but the eggs of a fresh lot, which
hatch in time to eat the spring wheats. Again, this large increase we
have ever observed in districts where rooks are few or much molested.
The rook is a constant visitor to the clover field; but when the plant
is young he is driven off, because the farmer “cannot think what else he
can come for but the clover buds;” and when he sees some of these
strewing the ground where the birds have been, he is confirmed in his
opinion: but, if he carefully looked at the buds themselves, he would
find them of a sickly hue, however recent the attack, and, if he looked
deeper he might find the real enemy.
Fortified, then, with repeated observations of this kind, if asked how
best to keep under wire-worms, we say most unhesitatingly, encourage the
rook: he is one of the farmer’s best labourers; and though, like John,
and Dick, and Hodge, he will sometimes run into mischief, it is surely
better to institute a judicious police than to condemn and execute
without very strong evidence.
Yarrell, in his beautiful “British Birds,” has the following remarks
upon this highly-important subject:—
The attempts occasionally made by man to interfere with the balance
of powers as arranged and sustained by Nature, are seldom
successful. An extensive experiment appears to have been made in
some of the agricultural districts on the Continent, the result of
which has been the opinion that farmers do wrong in destroying
rooks, jays, sparrows, and, indeed, birds in general on their
farms, particularly where there are orchards. In our own country,
particularly on some very large farms in Devonshire, the
proprietors determined, a few summers ago, to try the result of
offering a great reward for heads of rooks; but the issue proved
destructive to the farms, for nearly the whole of the crops failed
for three successive years, and they have since been forced to
import rooks and other birds to stock their farms with. A similar
experiment was made a few years ago in a northern county,
particularly in reference to rooks, but with no better success; the
farmers were obliged to reinstate the rooks to save their crops.
But as, perhaps, the most interesting account of the value of rooks will
be found in an extract from the _Magazine of Natural History_, vol. vi.
p. 142, we cannot do better than transcribe it:—
“In the neighbourhood of my native place (in the county of York),”
says the writer, Mr. T. Clithero, “is a rookery belonging to W.
Vavasour, Esq., of Weston, in Wharfdale, in which it is estimated
that there are 10,000 rooks; that 1 lb. of food a week is a very
moderate allowance for each bird, and that nine-tenths of their
food consists of worms, insects, and their larvæ; for, although
they do considerable damage to the fields for a few weeks in
seed-time, and a few weeks in harvest, particularly in backward
seasons, yet a very large proportion of their food, even at these
seasons, consists of insects and worms, which (if we except a few
acorns and walnuts in autumn) compose at all other times the whole
of their subsistence. Here, then, if my data be correct, there is
the enormous quantity of 468,000 lb., or 209 tons, of worms,
insects, and their larvæ, destroyed by the rooks of a single
rookery in one year. To everyone who knows how very destructive to
vegetation are the larvæ of the tribes of insects, as well as
worms, fed upon by rooks, some slight idea may be formed of the
devastation which rooks are the means of preventing.”
Let this, then, suffice for the rooks; but starlings, wagtails, larks,
and other birds, are also helpmates to the farmer; and therefore the
wanton destruction of these will certainly bring, nay, has already
brought, a great amount of trouble upon the cultivator of the soil.
The destruction we speak of has been committed by clubs and societies
established for the purpose; but, as their members are mostly filled up
with all sorts of prejudices—few being naturalists, or even accurate
observers—it becomes daily a matter of more pressing importance that
middle-class education, if not National-school teaching, should
recognise the value of the natural sciences.
2. The _Gout-fly_ (_Chlorops glabra_) and the _Saw-fly_ (_Sirex
pygmæus_) both lay their eggs below the first node or knot of the young
plant, which, as soon as they hatch, form maggots that eat out the
substance of the stems and the nodes, which thus become weakened and
ultimately break off, or, if left standing, the ears of corn as they
appear will be dried, whitened, and infertile.
In these, as in most cases of insect attacks, we have an occasional
blight of such extent as to destroy whole crops, against which we are
almost powerless, as we know so little of the economy of the creatures
by whom the mischief is caused; still, there can be little doubt but
that their periodical appearance, to the extent to cause them to be
recognised as _blights_, is due to the thinning of their enemies; and we
have always observed that a paucity of the _Hirundines_—the swallow
tribe of birds, their greatest enemies—is coupled with a great increase
of the smaller insects which it is the vocation of swallows, bats, and
others of the hawking insectivorous creatures, to take on the wing.
3. The _Wheat-midge_ (_Cecidomyia tritici_), also called the
Hessian-fly, is sometimes very destructive to the wheat crop. In 1860 we
observed the effects of this creature to a greater extent than we have
before known, in not a few instances rendering the crop scarcely worth
reaping. Upon this creature we sent the following notice to the
_Agricultural Gazette_ for August 30, 1862:—
The wheat-midge (_Cecidomyia tritici_) has been so destructive for
the last two or three years, that every fact connected with its
history ought to be of great interest. Curtis tells us that “in
Scotland one-third of the crop was lost, and the farmers suffered
severely in 1828 and the three following years;” whilst “in Suffolk
the yield[19] of wheat was one-third less in some districts in 1841
than was expected.”
[19] We believe this creature to be one of the most common causes of
deficient yield, so that a knowledge of its history is all-important in
estimating the value of a crop, which, as a rule, we should always put
lower in the seasons when this blight abounds.
The presence or absence of this insect is so important as affecting
the yield, that we now never fail to look for it in every crop upon
which we would offer a judgment in this respect.
It is easily detected in the larva state on opening some of the
chaff-scales—pales—of affected crops, as in the interior of these
will be found some minute larvæ (maggots) of a bright yellow or
orange colour. In the earlier period of the blossom these larvæ
will be found about the stamens and pistils; later, upon the
grain, which is always shrivelled and lost where the attack has
been made.
The colour of the maggots is so much like that of the red-rust as
often to be mistaken for it; the difference, however, between the
bunches of minute granular fungi and living worms will be made
apparent to the most careless observer by the assistance of a
common pocket lens. We find two terms in use for these yellow
appearances—namely, red-rust and red-gum; and as we have so often
found them employed indiscriminately, we would restrict the former
to the fungus,[20] thus—_Uredo rubigo_, red-rust; and _Cecidomyia
tritici_, red-gum. Our observations on the latter this year have
chiefly been made in the counties of Sussex and Gloucester, in both
of which we have seen this insidious enemy at work to an alarming
extent. In the former county, with a very limited extent of
red-rust; in the latter, the later and more delicate wheats have
both red-rust and red-gum in the same crop: and the interest of the
subject will be the more forcibly apprehended when we say that in
some crops, which, from a first glance at the straw and ears, we
should have put down as somewhere about thirty bushels per acre, we
have, after a more minute inspection of the ears, estimated at less
than twenty bushels; and, indeed, in one field which we have
examined during the last week (August, 1862), affected by the
_Cladosporium_, _Uredo_, and _Cecidomyia_, there will scarcely be a
yield in good grains of the amount of the seed sown.
[20] See _ante_, p. 185.
The fly which lays the eggs from which these yellow larvæ are derived is
of about the size of a gnat, and usually takes the wing in the evening,
in which case, if its enemies the bats are not numerous, smother fires
lighted towards sundown on the wind side of the fields are not only
destructive to large numbers, but act as an offensive notice to quit to
others. Curtis says:—
With regard to the Hessian-fly, even if its presence could be
ascertained in the early stages, it does not seem possible to
devise any means of destroying the eggs or young larvæ, unless
feeding off the blade with sheep would effect the object; and when
their progress is detected by their mischievous works, at a more
advanced period, nothing, I apprehend, but sacrificing the crop
would arrest them. It appears, therefore, to be an evil to which we
must occasionally submit; but, to guard against its immediate
recurrence, it will only be necessary to collect and burn the
stubble after the corn is reaped, by which means the larvæ and pupæ
which are concealed at the base of the stalk will, of course, be
destroyed.
Now, in reference to wheat stubbles, we would remark that the
old-fashioned plan of leaving them long as a protection, and, we may
add, a preserve of food for partridges, had its good effects in an
agricultural point of view; but if this be done, we advocate the burning
of the stubs on the soil, as they will thus act better as a manure,
while the destruction of insects by the process must be enormous. All
concur that modern agriculture suffers increasingly from insects; hence,
then, an extended study of their habits seems daily more desirable: and
we boldly assert that if our country schoolmasters would teach their
pupils to observe insect life, they may be doing more good to
agriculture than all our present so-called agricultural colleges and
schools put together.
4. The _Aphis flea_ (_Aphis granaria_) is a creature destructive to the
grain by “sucking the verdure out on’t.” We have this year (1864) seen
this insect, more especially the _apterous_—wingless—females, sticking
on to the green wheat ears to such an extent as to render a walk into
the crop a disgustingly dirty process. It would seem that a continuous
dry and warm season favours the increase of these creatures; but, as we
have always observed that the earlier sown wheats nearly always escape,
from their coming into ear and advancing to ripeness before the aphis
has increased its countless broods; so then we should recommend early
wheat sowing, wherever and whenever practicable, as a preventive of the
pest; in fact, the being in good time with all farm work has every
advantage.
5. The two affections of the grain in our table are widely different in
their modes of attack, but both tend to lessen the quantity of produce.
The first, the Ear-Cockle (_Vitrio tritici_) is an affection of the
grain, which at starting it will be well to distinguish from smut or
bunt. In the latter, the grain is filled with what appears a black
powder, the grains of which the microscope shows to be a fungus;[21]
whilst in the cockle the seed, which is purple externally—hence called
“purples”—is filled with what appears to be white cotton wool. This,
under the microscope, has the appearance of a multitude of eels. These
are, indeed, minute infusorial worms, and are exceedingly curious; the
smallest portion of the cottony substance taken on a pin’s point and
just moistened with water, often showing thousands of the eels under a
good instrument; for drawings and descriptions of which and good
drawings (after Bauer), we should recommend the reader to consult
“Curtis’s Farm Insects.” A damp season favours the production of these;
hence drainage and such conditions as increase the effects of damp and
cold are to be guarded against.
[21] See _ante_, p. 183.
The _Corn Moth_ is best known by the presence of a small, slightly hairy
maggot, which is found to eat the flour from the grain; this is the
larva of a small moth, probably the _Butalis cerealella_. It is easily
found in the chaff scales; and during the summer of 1861 we saw as many
as six in a single ear, and it was, indeed, one of the causes of the bad
yield of that year. We know of no remedy for this evil; but, perhaps, if
we were better acquainted with the habits of the moth itself, means
might be devised for taking it before the eggs are laid in the young ear
of corn.
6. The _Corn or Granary Weevil_ (_Calandra granaria_) and others.—These
attack corn in store, and probably differ in species according to the
kind of corn. This is a small beetle, the female of which makes a hole
in the grain and deposits an egg, which soon hatches into the maggot;
this eats out the grain with great assiduity until its partial period of
rest in the pupa state; which passed, the beetle finishes the work, and
may frequently be found in the interior of wheat.
The usual structures of granaries and corn-stores contribute to the
increase of this pest, as they are mostly dark and ill-ventilated
chambers. The best remedy is to expose the grain to the greatest
possible amount of cold, by spreading it on the floors in hard frosts,
and letting in light and air. Curtis quotes the “Bulletin des Sciences
Agriculture” for July, 1826, for the following plan:—“Lay fleeces of
wool, which have not been scoured, on the grain; the oily matter
attracts the insects amongst the wool, where they soon die, from what
cause is not exactly known. M. B. C. Payrandeau related to the
Philomatic Society of Paris that his father had made the discovery in
1811, and had since practised it on a large scale.”
7. The moth that visits granaries (_Tinia granella_) may here be
adverted to. The presence of the larvæ of the little grain moth may soon
be ascertained in the granary, when one finds several grains of corn
united by a web, to which will be attached bunches of small granules,
which are the exuviæ of the one or two caterpillars belonging to each
group of corns.
The best method of preventing this is thorough cleanliness, light, and
ventilation in the granary. If, however, the moth has got possession,
then we recommend sulphur to be burnt in iron pans—old saucepan lids are
as good as anything—stopping up all the crevices. This will be an
effectual remedy, not only for the moth, but for the weevils and other
insect pests; and if a pound of sulphur be occasionally burnt in the
barn, even rats must succumb to the gas which is generated.
8. The _Meal-worm Beetle_ (_Tenebrio molitor_), which generates commonly
in the meal-bins of this country, and the _T. obscurus_, which has been
introduced in American flour, are two forms of beetle, the larvæ of
which are “meal-worms.” These are best prevented by not keeping too
large a store of flour, always having this dry and in the best
condition, and storing, as far as possible, in a clean, light, and airy
position. Indeed, as Curtis remarks, “Cleanliness is the best guard
against these insects;” and we cannot better conclude this chapter than
by further quoting the following from this excellent author:—
In looking back to the variety of insects that feed upon corn, and
the multitudes that are often congregated in one heap, there can be
no doubt that a very large portion must be occasionally ground up
with the corn and consumed by the public. This is not only a
disagreeable fact, but it may be the source of very serious
consequences, for I think it not improbable that many diseases
might be traced to the insects which are converted with the
infested flour into bread, amounting to such a large percentage,
that if they have the slightest medicinal or deleterious qualities,
it is impossible to deny the influence they must exercise upon the
human system. I have known bushels of cocoa-nuts, which were every
one worm-eaten and full of maggots, with their webs, excrement,
cast-off skins, pupæ, and cocoons, all ground down to make
chocolate, flavoured, I suppose, with vanilla!