The Mexican cotton boll weevil

Material Information

The Mexican cotton boll weevil
Series Title:
Bulletin University of Florida. Agricultural Experiment Station
Newell, Wilmon, 1878-1943
Camp, A. F ( Arthur Forrest ), 1896-
Grossman, Edgar F
Place of Publication:
Gainesville Fla
University of Florida Agricultural Experiment Station
Publication Date:
Physical Description:
p. [221]-247 : ill., chart ; 23 cm.


Subjects / Keywords:
Cotton -- Diseases and pests -- Florida ( lcsh )
Cotton -- Diseases and pests -- Control -- Florida ( lcsh )
Boll weevil -- Florida ( lcsh )
Boll weevil -- Control -- Florida ( lcsh )
non-fiction ( marcgt )


General Note:
Cover title.
Bulletin (University of Florida. Agricultural Experiment Station) ;
Statement of Responsibility:
by Wilmon Newell, E.F. Grossman and A.F. Camp.

Record Information

Source Institution:
Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location:
Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management:
All rights reserved, Board of Trustees of the University of Florida
Resource Identifier:
027161527 ( ALEPH )
18172652 ( OCLC )
AEN4032 ( NOTIS )

Full Text


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source

site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida

Bulletin 180


Agricultural Experiment Station




Fig. 115.-Adult boil weevil with wings spread.

Bulletins will be sent free upon application to the Experiment Station,

May, 1926


P. K. YONGE. Chairman, Pensacola
E. W. LANE, Jacksonville
A. H. BLENDING, Leesburg
W. B. DAVIS, Perry
J. T. DIAMOND, Secretary, Tallahassee
J. G. KELLUM, Auditor, Tallahassee

WILMON NEWELL, D. Sc., Director
JOHN M. SCOTT. B. S., Vice Director and Animal Industrialist
SAM T. FLEMING, A. B., Assistant to Director
J. R. WATSON, A. M. Entomologist
ARCHIE N. TISSOT, M. S., Assistant Entomologist
H. E. BRATLEY, M. S. A., Asst. in Entomology
R. W. RUPRECHT, Ph. D., Chemist
R. M. BARNETTE. Ph. D.. Assistant Chemist
C. E. BELL, M. S. Assistant Chemist
E. W. COWAN, A. M., Assistant Chemist
J. M. COLEMAN, B. S., Assistant Chemist
O. F. BURGER, D. Sc., Plant Pathologist
G. F. WEBER, Ph. D., Associate Plant Pathologist
J. L. SEAL, M. S., Assistant Plant Pathologist
ROBERT E. NOLEN, M. S. A., Lab. Asst. in Plant Pathology
K. W. LOUCKS, A. B., Lab. Asst. in Plant Pathology
ERDMAN WEST, B. S., Lab. Asst. in Plant Pathology
D. G. A. KELBERT, Field Asst. in Plant Pathology
W. E. STOKES, M. S., Grass and Forage Crops Specialist
W. A. LEUKEL, Ph. D., Assistant Grass and Forage Crops Specialist
A. F. CAMP, Ph. D., Plant Physiologist, Cotton Investigations
W. A. CARVER, Ph. D., Assistant Cotton Specialist
EDGAR F. GROSSMAN, M. A., Assistant Entomologist, Cotton Investigations
RAYMOND CROWN, Field Asst., Cotton Investigations
A. L. SHEALY, D. V. M., Veterinarian
D. A. SANDERS, D. V. M., Assistant Veterinarian
C. V. NOBLE, Ph. D., Agricultural Economist
BRUCE MCKINLEY, B. S. A., Assistant in Agricultural Economics
H. G. HAMILTON, M. S., Assistant Agricultural Economist
OUIDA DAVIS ABBOTT, Ph. D., Head, Home Economics Research
GEORGIA WESTOVER, Assistant in Home Economics
HAROLD MOWRY, Assistant Horticulturist
G. H. BLACKMON, B. S. A., Pecan Culturist
W. B. TISDALE, Ph. D., Plant Pathologist, in charge Tobacco Experiment
Station (Quincy)
J. G. KELLEY, B. S. A., Lab. Asst. in Plant Pathology (Quincy)
JESSE REEVES, Foreman Tobacco Experiment Station (Quincy)
L. O. GRATz, Ph. D., Assistant Plant Pathologist (Hastings)
A. S. RHOADS, Ph. D., Assistant Plant Pathologist (Cocoa)
A. N. BROOKS, Ph. D., Assistant Plant Pathologist (Plant City)
STACY O. HAWKINS, Field Asst. in Plant Pathology (Miami)
J. H. JEFFERIES, Superintendent Citrus Experiment Station (Lake Alfred)
W. A. KUNTZ, A. M., Assistant Plant Pathologist (Lake Alfred)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)

K. H. GRAHAM, Auditor
RACHEL MCQUARRIE, Assistant Auditor





The cotton boll weevil has proven to be one of the most difficult
insect pests which farmers and scientists of this country have
been forced to fight. Coming into this country from Mexico in
1892 it has spread thruout the Cotton Belt in spite of all efforts
to prevent it. As a result of the arduous work done since that
date, however, certain methods of control have been developed
which are proving profitable to many' cotton growers. On the
other hand, there are still cotton growers who either do not
attempt to control the boll weevil or who carry out the first plan
they happen upon and consequently find cotton growing unprofit-
able. In this bulletin we will endeavor to present the control
methods now being used successfully, so that the farmer can
estimate the value of the various methods suggested to him and
intelligently apply the method best suited to his particular lo-
Since all successful methods of control are based on the life
history and habits of the boll weevil, there will be found in this
bulletin an outline of the weevil's life cycle with special stress
laid on those factors that are taken advantage of in the various
methods of control. It is hoped that a study of the information
presented herein may prove of value to the cotton grower who
wishes to obtain the best results from his attempts at boll weevil
The Mexican cotton boll weevil, Anthonomus grandis Boh., was
first described by Boheman in 1843 from specimens received from
Vera Cruz, Mexico. The boll weevil first became established in
the United States near Brownsville, Texas, in 1892, tho just how
it crossed the Rio Grande River is not known. Since then, the
weevil has spread over the entire cotton growing area except the
Southwest which appears to be too hot and dry for the weevil
and in Virginia and Illinois where very little cotton is grown.

S- I





The cotton boll weevil has proven to be one of the most difficult
insect pests which farmers and scientists of this country have
been forced to fight. Coming into this country from Mexico in
1892 it has spread thruout the Cotton Belt in spite of all efforts
to prevent it. As a result of the arduous work done since that
date, however, certain methods of control have been developed
which are proving profitable to many' cotton growers. On the
other hand, there are still cotton growers who either do not
attempt to control the boll weevil or who carry out the first plan
they happen upon and consequently find cotton growing unprofit-
able. In this bulletin we will endeavor to present the control
methods now being used successfully, so that the farmer can
estimate the value of the various methods suggested to him and
intelligently apply the method best suited to his particular lo-
Since all successful methods of control are based on the life
history and habits of the boll weevil, there will be found in this
bulletin an outline of the weevil's life cycle with special stress
laid on those factors that are taken advantage of in the various
methods of control. It is hoped that a study of the information
presented herein may prove of value to the cotton grower who
wishes to obtain the best results from his attempts at boll weevil
The Mexican cotton boll weevil, Anthonomus grandis Boh., was
first described by Boheman in 1843 from specimens received from
Vera Cruz, Mexico. The boll weevil first became established in
the United States near Brownsville, Texas, in 1892, tho just how
it crossed the Rio Grande River is not known. Since then, the
weevil has spread over the entire cotton growing area except the
Southwest which appears to be too hot and dry for the weevil
and in Virginia and Illinois where very little cotton is grown.

S- I

Florida Agricultural Experiment Station

At the present time the weevil also occurs thruout the larger
portion of Mexico, and southward to Guatemala and Costa Rica,
as well as in Cuba. Anthonomus grandis thurb4riae (Boh.)
Pierce, a variety of the boll weevil, has been found breeding on a
species of wild cotton in Arizona and vicinity.
The weevil progressed steadily across the Cotton Belt from
the original point of entrance, tho it was not until about 1911
that it was reported as having reached the western edge of
Florida. From there it continued eastward until in 1918 it had
invaded all of the Cotton Belt of Florida.
The results of the boll weevil invasion into this state were
particularly severe. The warm winters and wet summers com-
mon to this territory proved ideal for the development of the




"BOO0 "8l1
olo omol m




Fig. 116.-Yields of Sea Island and Upland cotton in Florida from 1912 to
1925 (in running bales).

weevil. An unusually large percentage of the weevils are able
to survive the mild Florida winters and these, with favorable
summer weather, are able to multiply with great rapidity. More-
over, it was found that Sea Island cotton, due to its slow fruiting

Bulletin 180, The Mexican Boll Weevil

habit and soft bolls, was unusually susceptible to boll weevil
damage. While it must be conceded that there were other forces
detrimentally influencing the production of Sea Island cotton,
yet it must also be conceded that it was the weevil which actually
stopped the growing of this cotton in Florida. By 1923 the pro-
duction of Sea Island cotton had fallen below 750 bales for the
entire United States and it was necessary to replace it with
Upland cotton. The substitution of Upland cotton for Sea Island
has been very slow and in the southern sections of the old Sea
Island belt very little cotton of any kind is grown at the present
time. In Fig. 116 is graphically shown the production of Sea
Island and Upland cotton in Florida during the period from 1912
to 1925.

The boll weevil, shown natural size in Plate I, Fig 1, is a small,
dark, grayish-brown beetle about 1/ of an inch long; commonly
found in the blossoms, squares or buds of the cotton plant. The
female lays its eggs in the squares or bolls of the cotton plant,
depositing them in cavities bored with its long snout. A small
grayish grub, called a larva, hatches from the egg. The larva
grows until it is about 1/4 inch in length, enlarging the cavity in
which it finds itself by eating away the surrounding tissue and
packing back the waste material. The larva changes to what is
termed the pupa. In this stage rudimentary legs, wings, and
other organs of the adult form can be seen. The pupa finally
changes into the young weevil, which cuts a hole in the wall of
the square and escapes from the cavity in which all the stages
of its development, consisting of egg, larva, pupa, and young
weevil, have taken place. Descriptions of the various stages of
the life history of the weevil together with some of its habits are
given in the succeeding pages.

The body of an average size weevil is about 3/16 inch long
and 1/16 inch broad. The snout is about half as long as the
body, making the weevil a little over 14 inch long when the snout
is extended. There is a great variation in the size of the adult
weevils, as shown in Plate I, Fig. 1. The variation in size is
attributed to the quantity and quality of food available while the
weevil is maturing within the cotton fruit; small or dried-out

Florida Agricultural Experiment Station

squares producing small weevils and larger and fresh squares
producing larger weevils. It is sometimes erroneously thought
that the larger weevils are females and the smaller weevils are
males; there are, however, large and small females and also
large and small males. The weevil does not change its size after
it emerges from the squares.
There is also a great variation in the color of the weevil,
ranging from a light reddish-brown in a newly hatched weevil,
to a dark grayish-brown or black in an old weevil. Weevils which
have spent the winter in hibernation are particularly dark in
color. The fore-legs are quite stout, with club-shaped thighs
bearing two spurs on the inner side of the lower ends, as shown
in Plate I, Figs. 2 and 3 (spurs indicated by arrows). The thighs
of the other legs bear only one spur each. Familiarity with the
size, shape and color of the body, and especially with the double-
spurred forelegs, should enable one to distinguish the boll weevil
from the numerous other insects commonly mistaken for it.


The egg (Plate II, Figs. 1 and 2) is very difficult to find as it
is almost colorless and only about 1/30 inch long and about 1/50
inch broad. The outer cover or shell consists of a tough, pliable,
pearly-white membrane, which permits the egg to be fitted easily
into the egg-pit bored by the weevil.
Egg laying is accomplished in a short time, the average length
of time required being about five minutes. The weevil first bores
a cavity for the egg in the cotton square or boll, usually as deep
as the snout is long; then turns about, lays an egg, and pushes it
down into the freshly bored hole, and ends the process by sealing
the opening with a gum-like material. A noticeable scar is soon
formed at this point. (Plate III, Figs. 1, 4, and 5.)
Normal egg laying always takes place in the cotton square or
boll, with the egg snugly packed among the immature pollen sacs
of the squares or on the inner side of the boll wall. Egg laying
in the cotton stem or bud is unknown. Under abnormal condi-
tions the egg has been found at the edge of the egg cavity, or
elsewhere on the outside surface of a square or boll. Eggs left
on the surface do not develop as they soon dry out or are eaten
by insects.





5 6

Fig. 1.-Weevils, natural size, showing variations. Figs. 2 and 3. Back and side view, seven times natural size. Arrow
points to spurs on forelegs. Fig. 4. All stages from egg to adult, natural size. Figs. 5 and 6. Boll weevil snout,
showing mouthparts at tip of snout. 6, side view, 5, looking into snout, mandibles opened-(Figs. 5 and 6, enlarged
15 times.)


Figs. 1 and 2. Boll weevil egg. Fig. 3. Newly-hatched larva. Figs. 4, 5, 6, and 7. Progressive stages in development of
arva. Figs. 8, 9, and 10. Progressive stages in development of pupa. Figs. 11, 12, and 13. Pupa changing to mature
weevil. (Figs. 1 and 3, 15 times natural size and all other figures 7 times natural size.)

Bulletin 180, The Mexican Boll Weevil

After the egg is laid, development continues at a rapid rate
and at the end of about three days a fully-formed, legless grub
or larva is ready to hatch. During cool weather, however, the
development may be so retarded that two weeks or more are
necessary for the egg to hatch.


Before hatching, the grub can be seen thru the transparent
egg shell or membrane. A relatively large head fills one end of
the egg-shell, while the body, almost doubled on itself, takes up
the remaining space. During the period of development from
the egg to the fully-formed, minute grub there has been no addi-
tion of food to that present in the egg at the time of laying;
merely a change in the egg material itself has taken place. The
first activity shown by the newly-formed grub is the cutting of
its way out of the egg membrane.
Just after hatching, the grub, like the egg, is very hard to see.
It is about 1/25 inch long and almost colorless, with the excep-
tion of the brownish head and jaws, Plate II, Fig. 3. It feeds
vigorously and shows a remarkable gain in size until at the end
of about seven days it measures about 1/4 inch in length and
slightly over 1/16 inch in thickness. In Plate II, Fig. 4, is shown
the fully-grown grub or larva. There is a great variation in the
sizes of fully-grown grubs which is attributed to the amount of
food available for the grub, little food making small grubs, and
an abundance of food producing large grubs. The rate of growth
is affected greatly by the temperatures to which the grubs are
subjected, either cool or extremely hot weather delaying the
process of development several weeks. Tho very few of the
eggs fail to hatch, a relatively large percent of the grubs fail to
develop, direct sunshine on the squares housing grubs, dry
weather and lack of sufficient food causing the death of a high
percentage of the grubs.


When the grub has finished feeding, its body shortens some-
what and flattens out. The grayish color of the interior, which
shines thru the thin and transparent body wall, disappears and
the grub starts another period of reorganization or development.

Florida Agricultural Experiment Station

This period of development is called pupation and we say that
the grub has changed to a pupa. During this period no food is
taken in. The pupa merely goes thru a series of. changes which
are to end with the formation of the adult weevil.
The cavity or cell, made by the grub's method of packing all
the waste materials against the inner walls, affords a snug rest-
ing chamber for the pupa. Here, protected from insect attack
and from the poisoning efforts of the cotton grower, the pupa
gradually develops wings, legs, snout and other adult organs (see
Plate II, Figs. 8 to 11). After about four days the development
of the pupa is complete and a fully-formed adult boll weevil is
ready to bore its way out of the square or boll in which its entire
development occurred. In Plate II, Figs. 3 to 13, are shown the
various stages from the newly hatched larva to the mature wee-
vil. (See also Plate I, Fig. 4.)

The soft body wall and more or less tender appendages of the
newly-formed weevil change within a day or two to a hard and
resistant covering. Having thus matured, the weevil bores its
way out of the square or boll. Usually several hours are required
for cutting the emergence hole in the square, tho occasionally
several days may be required to bore out of a tough-skinned boll.
Pictures of squares and bolls from which weevils have emerged
are shown in Plate III, Figs. 2, 3, and 6.
The percentage of adult weevils actually emerging from
squares and bolls in which eggs were originally laid is governed
largely by climatic and soil conditions. Where the soil is sandy
and the temperature high, records showing a mortality of the
immature weevil stages as high as 92 percent have been obtained.
In clay soils, on which leafy varieties of cotton are planted, 40
percent or less of the immature weevil stages may be killed from
various causes. It is thought that on the average about 1/3 of
the total number of squares in which eggs are laid produce
adult weevils.
In eating, the weevil bores a hole by using the jaws or man-
dibles which are located at the tip end of the snout. (Plate I,
Figs. 5 and 6.) The strong jaws cut and tear the material while
with prying and twisting motions of the snout circular openings
are cut out. Feeding on the cotton fruit or buds, and sometimes
on the leaves begins soon after the weevil bores out of its pupal


Bulletin 180, The Mexican Boll Weevil

cell. The female eats a great part of the material cut out of the
square in preparing an egg cavity, but seldom bores feeding
cavities as the male does.
The outer wall of the square is rather tough, consequently a
hole is bored thru it just large enough to allow the snout to pass
thru to the softer and much more palatable material within. The
weevil attacks the squares first but when most of the squares
have been punctured or shed from the plant the weevil turns its
attention to the cotton bolls. In its search for food the weevil
crawls over the plant, visiting most of the squares until the food
supply seems to be exhausted and then flies to an adjacent plant,
where the same procedure is followed.
After several days of feeding the newly emerged weevils be-
come sexually mature and mating and egg laying begin.
It is to these two habits of the weevil, feeding and egg laying,
that the loss of the cotton crop is directly attributed. Square
feeding may destroy only part of the pollen sacs, resulting in the
growth of a deformed cotton boll, or the square may be so injured
that it is shed by the plant. A similar loss is suffered by the
young bolls. Feeding in the cotton bloom, which takes place
during the morning hours, is in no way injurious. Feeding in
the plant bud probably does not cause any very serious damage,
and leaf-feeding is so slight that it is often erroneously stated
that the weevil does not feed on the leaves.
Egg laying in the square or in a small boll results in the shed-
ding of the square or boll. When a large boll is selected for egg
laying, only a single compartment or lock of cotton may be lost,
tho the entire boll may be ruined if a number of eggs are laid in it.
During the egg laying period, averaging about 35 days, the
female lays from 2 to 15 eggs each day, the total number of eggs
laid by each female averaging about 175. The greatest number
of eggs reported as having been laid in one day by a weevil, is
25; and the largest total number of eggs from one individual, 432.

Normally, only the adult weevils live over the winter in the
woods or fields, having gone into shelter with the coming of cold
weather. The adults that survive the winter enter the cotton
fields during the spring and as soon as squares are available they
start to lay eggs. Some of these eggs ultimately develop into


Florida Agricultural Experiment Station

mature weevils, forming the first generation. It takes from 25
to 30 days from the time the egg is laid until the weevil, develop-
ing from that egg, can itself start laying eggs. Weevils coming
into ,the field in the latter part of May will, in all probability,
have great grand children by some time in September.
As the successive generations of weevils develop during the
summer they will usually remain in the same field as long as
there are plenty of squares for food and egg-laying. When
squares become scarce, due to damage by the weevils or for other
reasons, the weevils start to fly about in search of food and ulti-
mately leave the field and fly to other fields; in other words, they
"migrate." In this way practically all of the cotton fields become
thoroly infested with weevils before fall.
As cool weather comes on the adult weevils get into sheltered
places in the field or in the woods and remain over the winter.
A large percentage of them die before spring but some remain
and part of these find their way into cotton fields in the spring.
The various phases of this yearly cycle will be discussed in
.detail below.


Average weather conditions in Florida bring the weevil out
of hibernation from early in March to late in June. A carefully
conducted experiment at Gainesville, Florida, in the spring of
1923, showed that out of 20,000 weevils, placed under hibernation
conditions during the previous fall, 5,449 weevils emerged; 75
percent of these emerged by May 30, and 90 percent by June 11.
It is a significant fact that under Florida conditions as high as
27 percent of the weevils placed in hibernation survived while
at Tallulah, La., over a period of six years only from 0.3 percent
to 5.9 percent of the weevils survived. Experiments conducted
at Madison, Florida, indicated that weevil emergence in cages
was usually completed by June 5 to 10.
Experimental evidence indicates that a relatively small per-
cent of the weevils emerge from hibernation, the others dying
during the winter; the death rate being higher in cold winters
than in mild winters. If a cold winter is experienced the cotton
grower may expect that a smaller percent of the weevils that
entered hibernation will be left to come into the fields; the total
number going into hibernation, however, will determine the num-


Bulletin 180, The Mexican Boll Weevil

ber of weevils to come out into the fields. If only 2 or 3 percent
of those going into hibernation survive the winter there still
may be plenty of weevils to ruin the crop if a sufficiently large
number went into hibernation. In interpreting winter weather,
observations concerning the number of weevils alive in the fields
during the fall should be combined with the weather records.
The number of weevils in the fall is dependent on food supply.
If toward the end of the season the cotton stays green, weevils
will continue to breed, but if the cotton dries up or is destroyed,
fewer weevils will be left for hibernation.
Another factor which tends to reduce the number of weevils
reaching the fields is the fact that when they emerge from hiber-
nation they tend to fly in all directions. If the flight takes the
weevil to cotton fields it has a place to feed and propagate; if
not, the weevil may become exhausted and starve to death even
tho endowed with reserve energy stored away for use during its
initial search for food. Were every weevil to hibernate success-
fully and on emerging in the spring find cotton fields, cotton
growing would be tremendously difficult if not impossible in
For some time the idea was prevalent that the over-wintered
weevil could be starved by late cotton planting, but such a plan
has been shown to be impractical, as the weevil may come out of
hibernation late in the season, and may live for some time with-
out any food at all.
Weevils emerging from hibernation and finding cotton before
squares are available feed on the buds and leaves of the cotton
plants. At least a part of these early emerging weevils will sur-
vive until squares are available for egg-laying. Combined with
these will be those weevils which come out of hibernation after
square formation has started. If these weevils are allowed to lay
eggs unmolested the number of weevils hatching in the field may
be so large that only the most vigorous control measures will
make the production of a crop possible.
As previously pointed out, the series of stages from egg to
adult weevil constitutes a "generation." Weevils hatching from
the eggs laid by the weevils emerging from hibernation are called
"first generation" of hatched weevils, and the weevils hatching
from their eggs are called "second generation," and so forth.
Now it is obvious that these generations are going to over-lap

232 Florida Agricultural Experiment Station

as they occur in the field. Hibernated weevils may lay eggs or
45 days or 10 to 15 days longer than the period from egg to g
in the life cycle. Likewise weevils continue to come out of hib r-
nation over a long period and start egg-laying as they reach he
fields. When the first generation of weevils hatches, there will
usually be, in the field, hibernated weevils just starting to lIy
eggs and still many weevils yet to come out of hibernation. Fi st
and second generation weevils may, therefore, start laying eg s
together and in any field will be found weevils of several genea-
This steady increase in the number of weevils in a field mak s
poisoning more difficult than if all the hibernated weevils lad
eggs at the same time and the first generation hatchedtogether,
thereby producing a wave effect in the infestation.

The formation of new generations goes on either until te
weevils are controlled by poisoning, or until there is no mo e
available material for feeding and egg laying. Then there is a
tendency for the weevil to move on in search of more cotton .
This activity has been termed weevil migration, and usual
takes place in Florida by the first of August. It is important
to remember that migration does not occur at a fixed date regar-
less of conditions but does occur whenever squares run short
Whenever a cotton field, on examination, is found to have more
than 60 or 70 percent of the squares punctured it is to be e
pected that some of the weevils have migrated or soon wi 1
migrate. This does not mean that the field will be left free
weevils-only a part will migrate and those left will be combine
with those hatching in the field so as to keep up a maximum
As previously stated the migratory flight may occur by th
first of August. Weevils will leave those fields with the heavies
infestations before they leave from fields with a light infestation
tho a large number of the fields may reach the weevil saturatio
point at about the same time and the result is usually a ver
heavy flight which overruns fields that were only lightly infested
up to that time. While the weevil does not ordinarily appear
be much of a flier, yet, when migrating, it may move great dis

Bulletin 180, The Mexican Boll Weevil

tances. While spreading across the United States the weevils
have been known to spread from 40 to 160 miles into new terri-
tory in a single season, tho not necessarily in one flight.
The question of migration is of utmost importance. The cot-
ton grower may poison the weevils which hatch in his field but
it is obvious that attempts to control the weevils when new ones
are arriving every day will be almost useless. This means that
the crop must be made before migration. The man who uses
early maturing varieties and keeps down the hibernated weevils
should make a crop easily in most years. The user of late varie-
ties will find himself, in many years, without a crop set when
migration takes place.
Having migrated primarily in search of fresh squares, and
having landed in new fields, the weevils continue to mate and lay
eggs. These activities are carried on until cool weather, when
the weevil is thought to prepare itself for the long winter's rest,
or hibernation.
The move into hibernation seems to take place when the mean
temperature is around 55 degrees Fahrenheit. All the weevils
do not leave the field in one day to make a general move for
hibernation but seem to go into cover a few at a time, many

Fig. 117.-Ideal hibernation quarters for boll weevils.

Florida Agricultural Experiment Station

remaining in the open cotton fields to be eventually killed by
frost. Some weevils fly into sheltered places which are high
and dry, tho the majority seem to crawl into whatever shelter is
present, crawling especially into the rubbish that accumulate
about uncared-for fences, in corn stubble, cotton burs, the debris
in timber land, Spanish moss, in fact, into anything that may
offer shelter. When such places for shelter are removed many
more weevils are exposed to killing temperatures.
The appearance of weevils from time to time during the winter
is due to a warming up of the least protected places into whi h
the weevils have crawled. A sudden cold snap following this
premature emergence often kills these weevils. Those weevils
which have burrowed their way well into a thick rubbish pil,
or into Spanish moss, are not quickly warmed up by the sun a d
consequently do not come out of hibernation until the mean tem-
perature of their hibernation quarters has reached about (5
degrees Fahrenheit.


Boll weevils may be reduced in numbers either by natural
causes such as weather; insect enemies and birds or by artificial
-means such as poisoning. During the early days of the boll
weevil invasion much time was spent in studying the factors
involved in natural control, while recently the bulk of the wo k
has been directed toward a study of artificial control, especially
the study of poisons. The early studies resulted in the increa e
of cotton growing in those territories that are so hot and dry i
summer that the boll weevil is largely reduced in numbers b
the destruction of the immature stages, and uncovered certain
things that could be taken advantage of as aids in the control of
boll weevils by poisoning. For that reason some space will be
allotted to various phases of natural control.

By far the most important factor in the natural control of th
weevil is weather. Hot, dry summers, as previously mentioned
are very destructive to the immature stages and the cotton grow-
ers in western Texas take advantage of this condition. While i
is true that the total yield of cotton in Texas has increased since
the advent of the weevil, yet an examination of the records show

Bulletin 180, The Mexican Boll Weevil

that the increase has been in those sections of the state which
were little used for cotton prior, to the weevil invasion and which
now enjoy success only because of the fact that the summer
weather controls the weevils, thus making cotton production less
expensive. Sections of Texas formerly considered highly desir-
able for cotton have in many cases shown both a decrease of total
production and a decrease in acre production since the coming of
the weevil.
Cold winters, by decreasing the numbers of weevils that live
thru the winter, constitute an important factor in weevil control.
The extension of cotton growing along the northern border of
the Cotton Belt has been brought about largely because of this
It is obviously impossible to control the weather in Florida;
and both mild winters, which permit a large survival of the
hibernating weevils, and wet summers, which permit a rapid
multiplication in the fields, must be faced. However, it is pos-
sible to minimize the effect of these weather conditions. The
removal of easily accessible hibernation places which would
otherwise protect the weevil thru a mild winter, and the planting
of cotton varieties with sparse foliage which lets the sun shine
thru to the soil to kill the immature weevil forms, are steps
toward satisfactory natural control.
Consideration of the cotton variety to be planted is often neg-
lected, tho it should be realized that the squares falling into the
shade of heavily foliaged cotton will be cooler and damper and
consequently in a much more favorable condition for the develop-
ing of the immature weevil stages than squares from sparsely
foliaged cotton which fall into the sun. Weeds as well as the
cotton plants may cause the ground to be shaded, and frequent
cultivation should be employed to keep the cotton field well
The advantages obtained from planting an early and prolific
variety of cotton are greatly enhanced by the proper use of fer-
tilizer. Under these conditions the fruit sets before the weevil
migrates from other fields, and the cotton can be picked and the
plants destroyed considerably before the weevil goes into hiber-
nation. This leaves the weevil with a period during which it
must survive without food, thereby forcing it to go into hiberna-
tion in a starved condition. Also it will be remembered that the

Florida Agricultural Experiment Station

weevils on emerging from hibernation fly in all directions wh n
not carried by the wind. Consequently the chances of the weev Is
finding a field planted in a locality away from where cotton was
planted the previous year will be less than if the cotton were
grown again in last year's field with the woods around it full
of weevils.
During the season a certain number of weevils are killed by
other insects and birds, tho the fact that the period from the
laying of the egg to the emergence of the adult takes place e -
tirely within the square gives the weevil a particular advantage
in evading both its insect and bird enemies. At present there is
no outstanding enemy of the weevil, tho the introduction of ene y
insects has been attempted and an alert watch is being kept for
such means of natural control.

Upon the discovery of the boll weevil in Texas an immedia e
fight for its control was launched. In 1895, C. H. T, Townsend
recommended that Paris green or London purple mixed at t e
rate of 1 pound to 150 gallons of water be applied as a spray
when the cotton bolls began to form, but this did not prove satis-
factory. Further attempts at poisoning were equally disappoin -
ing until 1908, when the senior author showed that the weevi s
could be profitably controlled by dusting lead arsenate on the
cotton plants. Since that time many other poisons besides lea
arsenate have been tried, resulting in the choice of calcium arse-
nate as the most economical poison for general use. At the
present time the farmer should limit himself to the application
of calcium arsenate either as a dust or mixed with syrup r
some other carrier.
A great deal of research work is now being carried on b
various government and state workers in an attempt to fin
suitable poisons which will be cheaper and more effective tha:
calcium arsenate and also to improve the quality of calcium
arsenate itself. This sort of experimental work requires not
only a knowledge of insects and chemistry but also a great variety r
of facilities for testing the various poisons. As soon as any ne
poison has been developed to the point where it can be recom
mended for general use, if such is done, the farmer will be give

Bulletin 180, The Mexican Boll Weevil

the information necessary for its proper use, and in the mean-
time will find it best to utilize the poisons recommended by the
state and government workers.
The farmer should avoid buying, at all times, proprietary mix-
tures with secret formulas, and traps of various sorts, unless they
are specifically recommended by a state experiment station or
government entomologists. At the present time only one poison
can be safely purchased for boll weevil control and that is cal-
cium arsenate, which should be purchased from a responsible
company, since it is important that it be of proper chemical com-
position and of a proper degree of fineness.
In order that poisoning may be carried out successfully it is
necessary that the cotton grower understand how the weevil gets
the poison after it has been distributed over the field. Calcium
arsenate is applied as a dust, or mixed with syrup and water as
a sticky mixture for mopping or for spraying. Each of these
forms of calcium arsenate poison will be discussed below.

Contrary to the early opinion that poison must be forced into
the shucks of the squares, it has been found that a uniform dis-
tribution of poison over the surface of the plant results in the
rapid poisoning of the weevils. This seems to be due to the
fact that the weevil touches the end of its snout to the surface of
the plant as it walks about and in this way picks up dust particles
on the rough jaws at the end of its snout when it walks across a
dusted surface. When the weeyil starts to feed, the poison par-
ticles which have adhered to the jaws are carried into the stomach
and the weevil is poisoned. Inasmuch as the female weevil usu-
ally lays only one egg in a square and must then move to another
square it is obvious that an even distribution of the dust over
the plant will result in some poison being picked up on the end
of the snout, causing the ultimate death of the weevil.
In using calcium arsenate for dusting it is necessary to have
a good brand complying with the following present standard
specifications: It should contain not less than 40 percent total
arsenic pentoxide, and not more than 0.75 percent water-soluble
arsenic; the density should be not less than 80 nor more than 100
cubic inches per pound. More than 0.75 percent water-soluble
arsenic would cause burning of the plants and the density speci-

Florida Agricultural Experimentk Station

fled above is that found most favorable for dusting. Calci m
arsenate dust obtained from reputable manufacturers will uu-
ally be found to conform to these specifications.
There are several types of dusting machinery on the mark t,
namely, hand dusting guns, one-mule two-row dusters, and t o-
mule three- to four-row dusters. A hand duster will usually t ke
care of 5 to 8 acres per season; a mule-drawn, two-row duster,
25 to 35 acres; and a three-row duster, 50 to 70 acres. All dust-
ing machines used for cotton should emit the calcium arsen te
in a fine cloud to insure an even distribution of the poison. T ey
should be regulated to deliver from 4 to 7 pounds calcium ar e-
nate per acre, depending on the size of the plants and the deg ee
of weevil infestation. Applications may be made at any ti e
during the day or night, tho.much better control is obtained fr m
night dusting due to the windstill atmospheric condition which
allows the dust to settle evenly. The presence or absence of d w
is not considered a factor favoring night dusting.
A great disadvantage in the use of powdered calcium arsen te
for dusting is that rains will wash it off, making another appli a-
tion necessary. To offset this disadvantage dusts with stick rs
have been tried experimentally but so far no form of calci m
arsenate for dusting has been as successful in resisting rain as
the syrup mixtures.

When the cotton plants are small it will often be found eas er
and cheaper to apply calcium arsenate in a liquid mixture. or
this sort of work the poison should be mixed with water a d
syrup. Such a mixture may be made by adding 1 pound of
calcium arsenate to 1 gallon of water and stirring until a smo th
paste is obtained. To this paste add 1 gallon of syrup, stirri g
until the mixture appears to be uniform. This will make a thi k
and sticky mixture. The proportions of syrup and water m y
be greatly varied, depending upon the thickness of the syr p.
Blackstrap is frequently used but experiments show that mu h
better results are obtained by using higher grades of syrup. T e
mixture should mop easily, stick well, and should not harden n
drying. Syrup mixtures must be used shortly after mixing e-
cause the syrup, on standing, will ferment with a result t

Bulletin 180, The Mexican Boll Weevil

increase in the content of water-soluble arsenic which will burn
the cotton plant. For treating small cotton plants, one gallon of
this mixture is sufficient for one application per acre.
The mixture is applied to the bud of each plant, using a stick
about two feet long with rags tied onto one end, mop-like.
Enough of the poison is applied to the bud by just brushing it
with the syrup-soaked mop. The poison can be carried best in
one-gallon cans into which the mop can be dipped and used for
stirring from time to time to insure an, even mixing of the cal-
cium arsenate which has a tendency to settle out. After the cal-
cium arsenate has settled the top fluid will not kill the weevil,
and so the mixture should be stirred frequently while being used.
Applications may be made at any time of the day. Light showers
do not wash the mixture off, but long, heavy rains remove the
poisons, necessitating another application which should be made
as soon as possible.
The syrup used in these mixtures does not attract the weevil,
tho when it is accidentally reached by the weevil, it is eaten
along with the calcium arsenate. The syrup in the mixture
causes the calcium arsenate to stick to the plants and when the
weevil's snout comes in contact with the mixture, whether feed-
ing takes place or not, some of the poison adheres to the snout
and later is carried to the weevil's stomach, thus poisoning the
Syrup mixtures are especially efficient for the treatment of
young plants, as the weevil feeds in the bud until the squares
form and become large enough to feed on.
Mopping the buds of the plants places the poison where the
weevil will be sure to get it. Applications should be started as
soon as the plants begin to show signs of squaring in order to
insure the killing of most of the weevils in the field. Such appli-
cations will continue to be very efficient until more than 12 to
15 squares per plant appear; after this their efficiency is lost,
since the weevils find plenty of squares without visiting the bud,
and to place the syrup mixture over the entire plant would be
too expensive a process. When the plants reach this stage cal-
cium arsenate dust should be applied.


Fig. 1. Weevil puncture on square. Figs. 4 and 5. Weevil punctures in
holes in squares and bolls.

bolls. Figs. 2, 3, and 6. Weevil emergence

Fig. 1. Boll weevil larva in square. Fig. 2.
2 natural size, figs. 3 and 4 twice natural

Larva in boll. Fig. 3. Larva in square. Fig. 4. Larva in boll. (Figs. 1 and


242 Florida Agricultural Experiment Station

With such a procedure the first application will have to be m de
about May 20 to June 1; and about three to five additional ap li-
cations will have to be made depending upon how long the wee is
continue to come into the fields. Such a procedure will usu ly
kill most of the weevils, tho a few may be left to start the infes a-
tion and poison may have to be applied later to protect the c p
that has been set. Where the hibernation quarters are very de e
and the weevils slow in emerging it will be necessary to conti e
the applications of dust or syrup until near the end of June.
In certain districts the Florida Method will be found higl y
effective and it has the additional value of completing the ent e
process of poisoning hibernated weevils at one time. This met od
is based primarily upon the results of numerous hibernating te s
which have indicated that almost 100 percent of the weevils h e
emerged from hibernation by June 5. At that time, cotton, if
planted about the first of April, would have in the neighborho d
of three to five squares per plant. Part of these squares wot d
contain boll weevil eggs or immature stages of the weevil and
many of them would contain, within the shuck, matured weevils.
If all of these squares are stripped from the plants in such a w y
that the matured weevils cannot escape, and are later destroyed,
all of the immature stages contained within the squares would re
killed, together with a considerable number of adult weev is
which had been picked with the squares. The remaining weev s
in the field, having no squares upon which to feed, would go -o
the buds of the plants and feed there until new squares ae
formed. An application of poison at this stage should kill m ;t
of the weevils in the buds, its efficiency being similar to that of
a pre-square application of either syrup or dust poison. The-
retically at least, this should leave a field clean or almost cle n
of weevils until such time as weevils may start to migrate fro
other fields. It seems evident, however, that in the actual app -
cation of this method under practical conditions on the farm, a
thoro clean-up will not be obtained, and at least some weevi s
will be left in the field to produce new generations. Likewise,
there are localities in Florida where the weevils are not entirely
out of hibernation by June 5, and where a certain amount f
reinfestation by hibernated weevils can be expected. Neverthe-
less, there are localities where the soil is light and the woods are
not dense and in these cotton growers may expect to find most
of the weevils out of hibernation and in the fields by June 5, and

Bulletin 180, The Mexican Boll Weevil

if a thoro clean-up is made, may expect to have fields reasonably
free from weevils until late in July, when weevils will start to
come from other fields.
It is important, however, that great care be used in the square
stripping process and in the subsequent application of poison,
since a comparatively small number of weevils left in the field
may cause considerable damage if the weather during June is
favorable to the weevils. Likewise, a few weevils may be ex-
pected to come in after the clean-up and combine with those
which have been left in the field when the treatment was applied.
Granting that conditions are favorable to the cotton and that the
method has been carefully applied it is improbable that weevils
will reach sufficient numbers to prevent the setting of bolls before
a reasonable crop has been set.
The cost of applying this method depends largely upon two
factors: First, the supply of cheap labor, available at the par-
ticular time at which this work should be done, and second, the
number of squares per plant at the time when the method is to
be applied. If the number of squares per plant exceeds five at
stripping time, the cost of the stripping will be greatly increased.
This latter factor is controlled by both the fertilizer and the
variety of cotton as well as the date of planting. Early varieties
which fruit very prolifically, such as Express, Trice, and King,
will have to be planted later than the more slowly-fruiting varie-
ties which are commonly used, such as Cook, Cleveland, and the
various varieties of Toole. Where any fertilizer is used at all
it will be advisable not to plant before the first of April, and
where the previously-mentioned early varieties are used, prob-
ably not before the seventh of that month. Likewise, the plants
should be spaced somewhat wider than if another method is to
be used, one plant to 15 or 18 inches being about right.
For those farmers living in districts where the soil and woods
are light this may prove to be one of the cheapest and most
effective methods for getting rid of the over-wintered weevils.
For those districts where the soil is heavy and cotton slow of
growth and the woods thick and cool, resulting in a late emer-
gence of the weevils, this method is of doubtful value.
Work done in Jackson County, on the heavy clay soil common
in certain districts, indicated that, on June 5, cotton would not
have any squares to strip nor would all the weevils be out of

Florida Agricultural Experiment Station

hibernation at that time. Under such conditions the successful
application of the Florida Method in its present form is probably
out of the question and dust or syrup applications should be
used, starting when the squares are as big as peas,
For the Florida farmer it is extremely important that some
method be utilized for controlling the hibernated weevils and the
utmost care should be directed to this phase of the work. Whether
dust, syrup mixture or Florida Method be used, the procedure
should be carried out thoroly and completely, for every female
weevil missed at this stage is liable to have thousands of progeny
in the field later in the season.

Poisoning Weevils Which Hatch in the Field

As previously mentioned, the poisoning of field-hatched weevils
may be used as the sole means of control or as an aid to early
season poisoning campaigns. The procedure generally recom-
mended calls for applications of dust at 4-day intervals until the
weevils are under control (usually 3 or more applications will
have to be made), starting when an examination shows that 10
percent of the squares are punctured, and repeating when the
infestation again rises to 10 percent. This method is not adapted
to Florida conditions for a variety of reasons, which will be
pointed out later, tho it may be adapted to districts which have
a comparatively low winter survival of weevils and good weather
for dusting in June and July. Under such conditions the dry
weather is supposed to largely control the hatching of the weevils,
making their increase in numbers very slow and only as many
applications are made as are necessary to keep the number of
weevils below the point where substantial injury will take place.
Several factors militate against the success of such a method
in Florida: a heavy emergence of weevils in the spring; June
and July weather which is normally very wet with almost daily
rains; and weevil migration which occurs about the first of
August making a short crop season. When the 10 percent infes-
tation is reached the farmer will have thousands of squares con-
taining eggs and immature weevils lying on the ground and a
large number of weevils actually laying eggs in the field. At the
same time the summer rains will probably have started and in
many years' the farmer will be faced with an almost daily rain-
fall. Under such conditions it would be almost impossible to

Bulletin 180, The Mexican Boll Weevil

keep down the weevils so that a crop could be made, and if
forced to combat a heavy infestation such as will likely occur
during the average year in Florida, the farmer will find himself
almost helpless. With a large number of weevils in the field,
artificial control is largely dependent upon consistently good
weather which will enable the farmer to keep dust on the plants,
and this cannot be done in most years in Florida due to the heavy
rainfall in June and July. Moreover, the early migration, com-
ing as it does about the first of August in Florida, forces the
farmer to make his crop with the utmost rapidity and he can-
not afford to delay weevil control by waiting for good weather.
On the other hand, if the cotton grower has done his early
season poisoning thoroly he may expect that there will be com-
paratively few hibernated weevils left in his field and as a con-
sequence the rate of increase will be very slow until well into
July. During this period there will be an opportunity to set a
good crop of bolls.
It may happen, however, that the weevils will increase to such
numbers that by the time the cotton squaring slows up, as it will
when a heavy crop of cotton has been set, there will be danger
of the weevils becoming numerous enough to damage large num-
bers of bolls and thereby reduce the crop. It may also be possible
that under certain conditions early season poisoning will still
permit the weevils to develop in large numbers late in June or
early in July, and consequently, before a crop has been set;
dusting will have to be resorted to under such circumstances.
The cotton grower should keep the closest sort of check on his
field, examining large numbers of squares from time to time and
recording the percent of punctured squares. If a good crop has
been set early in the season and it is only necessary to protect it
until it matures beyond the point when it is susceptible to weevil
damage, the grower may be able to wait until 20 or 30 percent
of the squares have been punctured before starting to dust; but,
if weevils start to increase in numbers before a good crop has
been set, dusting should be started at once. Under either condi-
tion three to five applications of dust should be made at 4- or
5-day intervals, with any applications washed off by rain replaced
immediately. These applications should be sufficient to protect
a crop until weevil migration, but if dusting had to be started to
make the setting of a crop possible more applications will prob-


Florida Agricultural Experiment Station

ably be necessary before migration. It can easily be seen from
this that it is extremely important to carry out the early season
poisoning thoroly in order to reduce the amount of poisoning
that will have to be done later.

The boll weevil is undoubtedly here to stay. There may be
years when it will do little or no damage but there will also be
years when it will make cotton growing, even with the best
measures of control, difficult and there will be many years which
do not reach either extreme. It is obvious that the farmer can-
not plant year after year, gambling on the occasional dry year.
Rather, he must adopt a method of control to be used and en-
deavor to perfect it to his local conditions. The poisoning of
hibernated weevils should be the first step in that control. If the
season is favorable, no additional poisoning will be needed, but
if it is unfavorable, the necessary poisoning of field-hatched
weevils should be carried out.
In using poison to control the boll weevil the farmer should
always remember that boll weevil control will not make cotton.
At best, boll weevil control only protects the cotton that is made
by the cultural methods used. If the best that the methods, seed
and soil used could have made without the boll weevil is a quar-
ter of a bale per acre the best method of boll weevil control ever
devised will not increase this yield a particle and probably will
not be sufficiently successful to allow one to make that yield.
It should also be remembered that the cost of applying one
application of poison to an acre of cotton is the same whether the
cotton makes a bale or a quarter :of a bale. Likewise, it can
easily be seen that a man can afford to put more money into
poisoning the boll weevil on an acre of cotton if he can obtain
a bale from that acre than if his maximum return is only a
quarter of a bale.
The days of the old easy-going methods of raising cotton in
Florida are past. There is just one answer to the boll weevil
situation and that is that we must raise more and better cotton
to the acre and plant correspondingly fewer acres. Instead'~of
buying gin-run seed for 20 acres, buy good seed for 10 acres;
put as much cultivation and hoeing on the 10 acres as were for-
merly put on the 20; and use more fertilizer on the 10 than was

Bulletin 180, The Mexican Boll Weevil 247

used on the 20. With such practices more money can be profit-
ably spent on boll weevil control on the 10 acres than could have
been spent on the 20 acres when farmed by the older methods.
All these things together make possible economical boll weevil
control that will return dividends.