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C576

ENT

1 NO. 18, SECOND SERIES. (REVISION OF NO. 14.)

mited States Department of Agriculture,

DIVISION OF ENTOMOLOGY.

THE MEXICAN COTTON-BOLL WEEVIL.

(Anthonomus grandis Boh.)
SCOPE OF THE CIRCULAR.

Cireular No. 6 was published in April, 1895, and contained a brief
report of the observations made up to that time, and the conclusions
based on those observations, concerning the Mexican cotton-boll weevil,
an insect of Central American origin which, during 1894, attracted con-
siderable attention in the cotton fields of south Texas. The investiga-
tion was continued
during the summer,
fall, and early winter
of 1895, especially by
Mr. Schwarz, who
visited Texas in May
and June and again
from October to De-
cember, and by Mr.
Townsend, who was
stationed in the State
during the greater
part of the summer.
The writer went to
Texas in December,
and in company with
Mr. Schwarz carefully
studied the condition
of affairs at that season and talked with many prominent cotton grow-
ers. The results of these supplementary investigations were published
in Circular No. 14, which was issued both in English and in Spanish.
During 1896 still other investigations were made by the gentlemen
mentioned and by Mr. C. L. Marlatt, who studied especially the ques-
tion of remedies, and the results obtained necessitate the publication of
still another circular on the subject. In this circular all of the essential
points of the previous circulars have been repeated, the section on
remedies has been entirely rewritten, and a paragraph has been added
on the work of the weevil during 1896.

Fia. 1.—Anthonomus grandis: a, adult beetle; b, pupa: ec, larva—all
enlarged.

GENERAL APPEARANCE AND METHOD OF WORK.

This insect is a small, grayish weevil, of the shape and general
appearance shown in fig. 1, @, and measuring a little less than a quar-
ter of an inch in length. It is found in the cotton fields throughout
the season, puncturing and laying its eggs in the squares and _ bolls.
The larve, of the shape and appearance shown at fig. 1, ¢, and measur-
ing a little over three-eighths of an inch in length when full grown

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live within the buds and bolls and feed upon their interior substance.
The squares attacked usually drop, but most of the damaged bolls
remain upon the plant and become stunted or dwarfed, except late in
the season, when they either dry or rot.

DISTRIBUTION.

This insect through its ravages caused the abandonment of cotton
culture around Monclova, Mexico, about 1862. Two or three years ago

.--Actual occurrences, 1895.
o--Points examined where no wee-
vils were found.

Fig. 2.—Map showing distribution of the Mexican cotton-boll weevil.

cotton was again planted in that vicinity, but the weevil immediately
reappeared and destroyed the crop. At Matamoras the weevil was
noticed eight or ten years ago. About 1898 it crossed the river at
Brownsville e, and in 1894 was noticed in the country around San Diego,
Alice, and Beeville. At the close of the season of 1894 the insect oecu-
pled a territory extending to the north a little beyond Beeville, a few
miles to the east of that point, and southwest to the neighborhood of
Realitos, on the National Mexican Railway. The greatest damage
seems to have been done along the lower Nueces River. During 1895,
and particularly in the latter part of the season, it extended its range
to a considerable extent, Toward the east it was found in moderate

Mr. Townsend found a few liv-

abundance along the valley of the Guadaloupe River at Victoria, Thomas-
ton, and Cuero. North of its old range it extended to Kenedy, Flores-
ville, and many points in the country lying between the latter place
and Cuero. <A single field was found near San Antonio which contained
large numbers of weevils, and in the same way a single field was found
far to the east at Wharton in which the weevils had appeared late in
the season. The exact localities where the insect was found during
1895 are indicated on the accompanying map.

WORK OF THE WEEVIL IN 1896.

It was feared that during 1896 there would be a further spread of the
weevil, but for some reason, probably on account of the severe midsum-
mer drought, there was not only no spread beyond the limits indicated
on the 1895 map, but, on the contrary, a shrinkage of the territory
infested. The main spread in 1895 took place in the autumn and at
the outer boundaries, as at San Antonio and at Wharton the weevil was
unquestionably killed by the winter frosts. In a field, for example,
near San Antonio, which was several times examined in 1895 by Mr.
Schwarz, Mr. Townsend, and by the writer, and in which the weevil
was extremely abundant down to the month of December, not a trace
of the insect could be found in 1896. In 1896 the drought prevented
the “make” of the top crop at many points, and there was little food
for the autumnal generations of the weevil, and therefore a lesser spread
from the localities of successful hibernation.

NATURAL HISTORY AND HABITS.

The insect passes the winter in the weevil state. It can be found on
the cotton plant until late in December, and, in fact, as long as any
portion of the plant is green.
It is found most abundantly
in the early winter hidden be-
tween the involucre and the
boll, and later it frequently
works its way down into the dry
and open bolls. All the speci-
mens found by Mr. Schwarz in
such situations in the late
spring of 1895 were dead; but

ing in March. The dry boll is
probably not a frequently suc-
cessful hibernating place.
Judge 8. G. Borden, of Sharps-
burg, however, writing under
date of January 27, 1896, states
that the weevil at that time
was being found nearly every Fig. 3.—u, newly Laicied larva in young square; b,
day in the dry bolls; but this eT AU Sen situ; ec, pupa in young
statement lacks the signifi-
eance which it might otherwise have had as bearing on the question of
hibernation from the fact that no heavy frost had probably occurred up
to that time at Sharpsburg.

With: the cutting of the plants or with the rotting or drying of the

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bolls as a result of frost, the adult weevils leave the plant and seek
shelter under rubbish at the surface of the ground, or among weeds and
trash at the margin of the fields. Here they remain until the warm
days of spring when they fly to the first buds on such volunteer plants
as may come up in the neighborhood. They feed on these and lay
their eggs on the early squares, and one, or perhaps two, generations
are developed in such situations, the number depending upon the char-
acter of the season and the date of cotton planting. By the time the
planted cotton has grown high enough to produce squares the weevils
have become more numerous, and those which have developed from the
generation on volunteer cotton attack the planted cotton, and through
their punctures, either for feeding or egg-laying, cause a wholesale
shedding of the young squares. It seems to be an almost invariable
rule that a square in which a weevil has laid an egg drops to the ground
as a result of the work of the larva; in the square on the ground the
larva reaches full growth, transforms to pupa, and issues eventually as
a beetle, the time occupied in this round approximating four weeks.
Later,-as the bolls form, the weevils attack them also, and lay their

Fig. 4.—Mature boll cut open at left, showing full grown larva; the one at the right not cut, and
showing feeding punctures and oviposition marks.

eggs in them, and the larve develop in the interior just as with the
squares. The bolls, however, do not drop. Fig. 8, @ and b, show the
larvee in the squares, and ¢; a young boll eut open and the pupa in its
customary position.

There is a constant succession of generations from early spring until
frost, the weevils becoming constantly more numerous and the larvee
and pup as well. A single female will oceupy herself with egg-laying
for a considerable number of days, so that there arises by July an inex-
tricable confusion of generations, and the insect may be found in the
field in all stages at the same time. The bolls, as we have just stated,
do not drop as do the squares, but gradually become discolored, usually
on one side only, and by the time the larva becomes full grown gener-
ally crack open at the tip. While one usually finds but a single larva
in a square, as many as twelve may be found in a full-grown boll. In
any case, however, the hatching of a single larva in a boll results in the
destruction of the boll to such an extent that its fiber is useless. Where
no serious frost occurs in December, the insects all, or nearly all, reach
maturity and enter hibernating quarters, although larvee have been

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found in January at Sharpsburg. Whenever a heavy frost comes in this
month, or before, the observations of last fall show that those insects
which have not reached the beetle stage are nearly all killed. From
this fact it follows that the insect will not probably prove as injurious
in other portions of the cotton belt as it is in southern Texas.

It was found during the latter part of 1895 that the weevil was pres-
ent in a number of localities in which it was not known by the planters
themselves to occur. It is important that every planter who lives in or
near the region which we have mapped out should be able to discover
the weevil as soon as it makes its appearance in
his fields. Where a field is at all badly infested
the absence of bloom is an indication of the pres-
ence of the insect. In the early part of the sea-
son the weevils attack the squares first, and these
wilt and drop off. A field may be in full blos-
som, and as soon as the insect spreads well
through it hardly a blossom will be seen. This

dropping alone, however, is not a sufficient indi- (7 4
cation of the weevil’s presence. Squaresareshed \.% ¢ \¢ ( |
from other causes, but if a sufficient number of © //*4 y
fallen squares are cut open the cause will be ap- ij oN!

parent. The characteristic larva of the weevil
maleberduite readily recognizable on comparison 19-5. Late fall boll, show.
with the figures which we publish herewith. tween boll and involucre.
As stated above, the bolls do not drop. The
punctures made by the weevils in feeding, however, are comparatively
characteristic, and where a boll is discolored and has begun to crack at
the tip the larva or the pupa can be seen without trouble on cutting it
open. Late in the season the weevils themselves will be found between
the involucre and the boll, as shown in fig. 5, or in their absence the
feeding marks and the yellow, granular excrement which collects in the
involucre at the base of the boll are excéllent indications

POPULAR NAMES.

In south Texas, among Spanish-speaking people, the insect is gener-
ally known as the “‘picudo,’’ a descriptive name which refers to the
snout or beak of the insect. English-speaking planters generally referred
to the insect at first as “the sharpshooter,’ a term which for many
years has been applied to any insect which causes through its punctures
the shedding of the squares or the rotting of the bolls. As there are
several native insects that are commonly called sharpshooters, and
which, though injurious, are by no means to be compared with this
insect, it becomes necessary to discourage in every way the use of the
word sharpshooter as applied to this weevil. This was attempted in
the first edition of the circular by illustrating one of the commonest of
the insects ordinarily termed sharpshooters, calling attention to the
radical differences which exist between it and the weevil under consid-
eration. The adoption of the term “‘ Mexican cotton-boll weevil’’ for
the new pest is recommended. The term sharpshooter is now much
less generally applied to the weevil than it was at first. Planters gen-
erally now refer to it as the boll weevil, or the Mexican weevil, or the
Mexican boll weevil.

PARASITES AND NATURAL ENEMIES.

It is safe to say that little assistance will be derived from the work
of natural enemies and parasites upon this insect. Of the former none
of any importance has been found. Several parasites, however, have
been found to attack it, and in one or two localities some little good
has resulted from their work. They have been abundant only, however,
late in the season, after the weevil has completed its damage for the
year, and at a time when a minimum of good can be accomplished by
the destruction of the larve. The majority of the weevils in a given
field fail to hibernate successfully, being killed by cold weather or some
other cause, so that the work of parasites at this time does not count.
Careful estimates, however, show that from 15 to 20 per cent of the
weevil. larvee in fallen squares in November, 1895, at Beeville and
Kenedy were destroyed by parasites.

REMEDIES.

In considering the matter of remedies it should be understood at the
outset that experience has shown that none of the general applications
of insecticides is of the slightest value against this species as a means
of clearing infested fields. The weevil in its work in growing cotton
is thoroughly protected against poisons, breeding as it does within the
blossoms and squares. As demonstrated by the experience of the
spring of 1896, poisons may, however, be used as a means of destroying
overwintered beetles on volunteer cotton. The beetles which have sur-
vived the winter collect in the early spring on the first sprouts which
appear on old cotton and eat the partially expanded leaves and the
tender leaf stems, and at this stage can be poisoned by the application
of an arsenical to this new growth. To do this it will be necessary to
thoroughly spray the growing tips, and this should be done when volun-
teer cotton is very small, preferably mere sprouts: or bunches of leaves
an inch or two in length; later on the growing parts can not be easily
reached. With an ordinary knapsack pump a field may be gone over
rapidly and the volunteer cotton thoroughly treated, the nozzle being
directed at-each growing tip. The first application should be made as
soon as the volunteer plants sprout, and perhaps repeated two or three
times within as many weeks. As ordinarily cultivated, the number of
volunteers is small and the time required for the thorough spraying of
such plants will not be great. <A strong solution should be applied,
viz, 1 pound of the poison to 50 gallons of water, because no harm will
be done if the volunteer plants are ultimately killed by the poison.

The practicability of this method has been demonstrated, but it has
been abundantly shown that the very best system of control of the
weevil is in a system of cultivation of cotton, to be later described,
which will prevent all possibility of volunteer growth whatever. The
poisoning and the other palliative measures relative to volunteer
erowths are given, therefore, merely as a means of correcting an evil
which may result if the cultural system referred to has been neglected.
These remarks apply, for instance, to the trap system, which we have
hitherto recommended among others. This consists of attracting the
earliest beetles to a few cotton plants left at convenient points and
protected from winter killing by forced watering, so that they will
branch out and acquire buds often in advance of volunteer cotton.
From these the beetles may be collected by hand when they are attracted

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Say
to them on the first warm days, or, preferably, these plants may be
poisoned, as already suggested.

The fact that the spring generation develops only upon volunteer
cotton has suggested the possibility that the insect will not spread
beyond the region where volunteer cotton will grow in spring, but
unfortunately this possibility is by no means absolutely to be relied
upon. Nevertheless, the destruction of such volunteer plants as come
up in cornfields and in abandoned fields which the previous year were
planted to cotton, unless they be systematically poisoned, can not be
too strongly recommended, for it is a matter of observation that the
shade afforded by the corn or the rank-growing weeds which come up in
abandoned fields is especially favorable to the development of the weevils.

While the plants are young, and where labor is as cheap as it is in
south Texas, a great deal of good can be accomplished by picking and
burning the fallen squares, and if this is done promptly a large num-
ber of the insects will be destroyed. It should be done at least twice,
at intervals of three weeks, during the period while the plants are
small. This method becomes impracticable, however, as soon as the
plants begin to branch out, on account of the difficulty of finding the
squares on the ground.

The idea of picking the affected bolls during the cotton picking was
suggested in the writer’s first published account of this insect. It was
thought that the affected bolls could be so readily recognized that
many thousands of the insects could be destroyed by the cotton pickers
by picking these affected bolls and carrying them away in a separate
receptacle to be burned. The amount of extra labor involved in this
operation, however, would be very considerable, and the affected bolls
in many instances are not to be recognized at a glance.

During the past year Mr. Stronhall, of Beeville, has devised a
machine for jarring the affected squares and blossoms from young cot-
ton plants and collecting them at the same time. This apparatus has
been given a partial trial the past season, but was not seen at work by
any of the entomologists engaged in the investigation. It is arranged
to brush the cotton from both directions vigorously, and the loosened
bolls and squares are caught on receiving trays and ultimately burned
or otherwise destroyed. The brushes work in opposite directions and
strike the cotton plants on either side. It can be adjusted to plants of
different sizes.

The careful investigation of this weevil during the past two or three
years by the Division of Entomology has fully demonstrated the
supreme importance of the cultural method of control, to which fact
we gave special prominence in our first circular on this insect. There
can be no question now that in the proper system of growing cotton a
practically complete remedy for the weevil exists. In the first place, it
has been established beyond question that the conditions of cultivation
which make volunteer growth possible also make the continuance of
the weevil inevitable. Of first importance is the early removal of the
old cotton in the fall, preferably in November or earlier. This can be
done by throwing out the old plants with a plow, root and all, and
afterwards raking them together and burning them. This treatment
should be followed, as promptly as may be, by deep plowing, say to a
depth of 6 or 8 inches. This leaves the field comparatively clean of old
cotton stalks, facilitates thorough cultivation the following year, and,
at the same time, collécts and destroys all of the weevil larvee and pup

ISONIAN INSTITUTION LIBRARIES

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8 3 9088 01272 6758

in the cotton at the time, and also most of the adults. The escaping
beetles will be buried by deep plowing, and will not again reach the
surface. Few, if any, of them will succeed in hibernating in the absence
of the ordinary rubbish in the fields in which they winter. Fields treated
in this way have given a practical demonstration of the usefulness of
the method.

The greatest danger from the weevil is due to the presence of volun-
teer cotton, which means early food for the weevils in the spring and
abundant means for their overwintering, and the effort made to retain
volunteer and get early cotton, or the “first bale,’’ is a very serious
menace to cotton culture within the weevil district.

This cultural method, if generally practiced, will undoubtedly prove a
perfect remedy for upland cotton, and will vastly reduce weevil damage
in the lowlands, where the weevil is more apt to winter, perhaps in
adjoining woods or roadside vegetation. The early removal of cotton
by the means suggested is especi ally advised whenever the presence of
the weevil shows that the picking of a top crop is problematical. In
such instances it would be well to uproot and destroy cotton stalks in
September or October, as would have been thoroughly feasible for much
of the upland cotton in 1896. If this cultural method can be enforced,
either by State legislation or by the cooperation and insistence on the
part of landowners that their renters shall carry out the system out-
lined, the weevil difficulty can undoubtedly in very large measure be
overcome.

In connection with the system of fall treatment of the cotton, con-
stant and thorough cultivation of the growing crop as late as possible
is of considerable value, and is also what should be done to insure a
good yield. With a crossbar to brush the plants many of the blos-
soms and squares containing weevils will be jarred to the ground and
buried, together with those already on the ground, in moist soil, and
a large percentage of the material will rot before the contained insects
have developed.

It will be greatly to the interest of all growers of cotton in the prolific
district lying to the northeast of the region at present infested to urge
the passage of an act during the session of 1896-97 which will bring
about the enforcement of remedial work in 1897. This act should pro-
vide for the appointment of commissioners in each county upon the
application of a certain number of the citizens of that county. These
commissioners should be empowered to enforce remedial work, to levy
penalties, or to have the work done by their own agents, the cost to be
assessed upon the property. It will be well to let this law have a wide
bearing and not to confine its apphcation to this particular insect, but
cover all injurious insects, in case of future emergencies of a similar
nature. Such a law should be passed in every State in the Union.
Though it might remain inoperative for years, its application would be
available in case of any sudden emergency, such as the introduction
from a foreign country of a new injurious insect, or the sudden maulti-
plication and spread of any one of our native species.

L. O. HOWARD,

Approved : Entomologist.

Cuas. W. DABNEY, Jr.,
Assistant Secretary.

WasHINGTON, D. C., February 4, 1897.

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