The Mexican cotton-boll weevil (Anthonomus grandis Boh.)

Circular No. 14,Second Series. (Revision of No.6.)

United States Department of Agriculture, DIVISION OF ENTOMOLOGY.

THE MEXICAN COTTON-BOLL WEEVIL.

(Anthonomusgrandis Bob.)

SCOPE OF THE CIRCULAR.

Circular No. 6

was

published in April, 1895,

and

contained a brief reportof the observations

made up

^to that time,

and

the conclusions basedonthose observations,concerning the

Mexican

cottonboll weevil, an insect of Central

American origin

which, during 1894, attracted considera- ble attention in the cottonfieldsofsouth Texas.

The

investi- gation

was

continued during the summer,

fall,

and

earlywinter of 1895, especially

by

Mr. Schwarz,

who

visitedTexasin

May and June and

again from October to De- cember,

and by

Mr.

Town

send,

who was

stationedinthe State

during the greater part of the summer.

The

writer

went

to Texas in December, and in companj- with Mr.

Schwarz

carefully studied the condition of affairs at that season and talkedwith

many

prominent cotton growers.

The

objectofthe presentcircularis tolay beforecot- ton planterstheresults of this supplementaryinvestigation. In order to

make

itcompleteinitself,suchfactsas areneeded arerepeatedfrom CircularNo.6.

FlG.l. Anthonomus grandis: a,adult beetle; b,pupa:

enlarged.

larva—all

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 alittlelessthana 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

larvre,of theshape

and

appearance

shown

at fig. 1, c,

and

measur-

l

2

ing a little over three-eighths of an inch in length

when

full grown,

live withinthe

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 inthe season,

when

they eitherdry orrot.

DISTRIBUTION.

This insect through its ravages caused the

abandonment

of cotton culturearound Monclova, Mexico, about 1862.

Two

orthreeyears ago

Fig.2.

—

MapshowingdistributionoftheMexicancotton-bollweevil.

cotton

was

again planted in thatvicinity, but the weevil immediately reappeared

and

destroyed the crop.

At

Matainoras the weevil

was

noticed eight or ten years ago.

About

^{1893 it} crossed the river at Brownsville,

and

in1891

was

noticedin thecountry around

San

Diego, Alice, and Beeville.

At

theclose ofthe season of 1891 theinsectoccu- pied a territoryextending to thenorth a little beyond Beeville, afew miles totheeast of that point, and southwest tothe neighborhood ot Bealitos, on the National

Mexican

Railway.

The

greatest

damage

seems to

have

been done along thelowerNueces River.

During

1895,

and

particularly inthe latterpartof theseason, ^itextended its range to a considerable extent.

Toward

the east it

was

found in moderate

abundance

along the valley of the

Guadaloupe

River at Victoria, Thomaston,

and

Cuero.

Xorth

of itsoldrangeitextended toKenedy, Floresville,

and many

points in the countrylying between the latter place

and

Cuero.

A

^{single held}

was

found near

San

Antonio which contained weevilsinlarge numbers,

and

inthe

same way

asingle held

was

found far to the east at

Wharton

in which the weevils

had

appearedlate in the season.

The

exact localities

where

theinsect

was

found during1895 are indicatedon the

accompanying

map.

NATURAL HISTORY AND

HABITS.

The

insectpasses the winterinthe weevil state. Itcan be found on the cotton plant until late in December, and, in fact, as long as

any

portionofthe plantis green. Itis foundmost abundantlyin theearly winter hidden between the in-

volucre

and

theboll,

and

laterit

frequentlyworksits

way down

into the dry

and

open ^bolls.

All thespecimens found

by

Mr.

Schwarz

in such situations in the late spring of 1895 were dead; but Mr.

Townsend

found a few living in March.

The

dry boll is probably _{not a} fre-

quently successful hibernating place.

Judge

^S. G. Borden,of Sharpsburg, however, writing underdateofJanuary27,1896, states that the weevil at that time

was

being found nearly everydayinthe drybolls; but this statement lacks the sig- nificance which^it

might

other- wise

have had

as bearing on thequestionofhibernationfrom

the factthat no heavyfrost

had

probably occurred

up

to that time at Sharpsburg.

With

the cutting of the plants or with the rotting or dryingof the bolls as a resultof frost, the adult weevils leave the plant

and

seek shelterunderrubbish atthe surfaceof theground,or

among weeds and

trash atthe margin of the fields.

Here

they remain until the

warm

daysof spring,

when

theyflyto thefirst

buds

on suchvolunteer plants as

may come up

in theneighborhood.

They

feedonthese

and

lay their eggs on the early squares,

and

one, or perhaps two, generations are developedin such situations, the

number

depending

upon

the character of the season

and

thedate 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 gen- eration on volunteer cotton attack the planted cotton,

and

through their punctures, either for feeding or egg-laying, cause a wholesale sheddingof the

young

squares. ^It seems tobe an almost invariable rulethat a squarein whicha weevilhaslaidanegg dropstotheground asaresult of the

work

ofthelarva; in the square on the ground the larva reachesfull growth, transformsto pupa,

and

issueseventually 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.3.—a, newly hatched larva in young square;b,

nearlyfall-grownlarva insitu; c.pupainyoungboll picked from ground.

eggs in them,

and

the larva? develop in the interior just as with the squares.

The

^bolls, however, do not drop. Figs. 3, a,

and

3, b,

show

thelarvae inthe squares, and fig. 3,c, showsa

young

bollcutopen

and

the

pupa

ⁱⁿits customaryposition.

Thereis a constantsuccession of generationsfromearly springuntil frost, the weevils

becoming

constantly

more numerous and

the larva?

and pupae aswell.

A

^{singlefemalewill}occupyherselfwithegg-laying fora considerable

number

ofdays,sothat therearises

by

Julyaninex- tricable confusion of generations,

and

theinsect

may

be found inthe field in allstagesatthe

same

time.

The

bolls,as

we

havejuststated, donotdropasdo.the squares,butgradually

become

discolored,usually on oneside only,and

by

the timethe larvabecomesfull-grown generally Crack openat thetip.

While

in asquare oneusuallyfinds buta sin- gle larva, ina full-grown bollas

many

astwelve have beenfound. In

any

case, how- ever, the hatch- ing of a single larva in a boll results inthede- struction of the boll to such an extent that its fiber is useless.

Where

no seri-

ous frost occurs in

December,

the insects all,

or

nearly

all, reach maturity

and

enterhiber- natingquarters, althoughlarva?have been found onintoJanuaryatSharpsburg.

When-

ever 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 probablynot proveas injurious inother portionsofthe cottonbelt as ^itis in southern Texas.

It

was

found duringthelatterpart of 1895 that the weevil

was

present ina

number

oflocalitiesinwhichit

was

not

known

by

the plantersthemselves to occur. Itisimpor- tant that every planter

who

lives inor 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

afield is at all

badlyinfested the absenceof

bloom

is an indica- tion of the presence of the insect. In the early part of the season the weevils attack the squares

first,

and

thesewilt

and

dropoff.

A

^field

may

be

in fullblossom,

and

as soon as theinsectspreads well through ^it hardly a blossom will be seen.

This dropping alone, however, is not a sufficient indication of the weevil's presence. Squares are

Fig.^4.

—

Maturebollcutopenatleft,showingfall-grownlarva;the oneatthe right not cutandshowingfeeding punctures andovipositionmarks.

shed from othercauses, butifa sufficient

number

Fig.5.

—

Latefallbollshow- ing how beetles hide be- tweenbollandinvolucre.

of fallen squares are cut open the cause will be

apparent.

The

characteristic larva of the weevilwill bequite readily recognizableon comparisonwith the figureswhich

wo

publish herewith.

As

stated above,tlie bolls donot drop.

The

punctures

made by

the weevilsinfeeding,however,arecomparativelycharacteristic,

and where

aboll is discolored

and

has

begun

to crack at the tipthe larvaor the

pupa

canbeseenwithouttroubleoncuttingitopen. Lateinthe season the weevils themse.veswillbefoundbetween the involucreand theboll, as

shown

in fig. 5, or in theirabsence the feeding

marks and

the yel- low,granular excrement which collects in the involucre at thebaseof the boll are excellent indications.

POPULAR NAMES.

In south Texas,

among

Spanish-speakiugpeople, theinsectis gener- ally

known

asthe "picudo,'⁷a descriptive

name

w^Thichrefers tothesnout or

beak

of theinsect. English-speaking planters generallyreferred to theinsectat ^first, as "the sharpshooter,⁷⁷ aterm which for

many

years hasbeen applied to any insect which causes through its punctures the shedding of the squaresor the rottingofthebolls.

As

there aresev- eral native insects thatare

commonly

called sharpshooters,

and

which, thoughinjurious, are

by

no

means

to be

compared

with this insect,it

becomesnecessarytodiscourageinevery

way

the useofthe

word

sharp- shooterasappliedto this weevil. This

was

attemptedinthefirstedition ofthe circular

by

illustratingoneofthe

commonest

ofthe insectsordi- narilytermed sharpshooters,calling attentiontotheradical differences whichexist between ^it

and

the weevilunder consideration.

The

adop- tion oftheterm^uMexicancjtton-bollweevil'⁷forthe

new

pestisrecom- mended.

The

term sharpshooteris

now much

less generally appliedto the weevil than it

was

at first. Planters generally

now

refer to it as the boll weevil, orthe

Mexican

weevil, or theMexican bollweevil.

PARASITES AND NATURAL ENEMIES.

Itis safe to say that littleassistancewill be derived from the

work

of naturalenemies

and

parasitesupon this insect.

Of

the formernone of

any

importancehave beenfound. Severalparasites, however,have been found to attack it,

and

in one or

two

localities

some

little good has resulted from their work.

They

have onlybeen abundant, how- ever, latein the season, afterthe weevil hascompleted its

damage

for the year and ata time

when

a

minimum

of good can be accomplished bythe destruction of thelarva.

The

majorityof the weevilsina given field failto hibernatesuccessfully,being killed

by

cold weatheror

some

othercause, so that the

work

of parasites at this time does notcount.

Careful estimates, however,

show

that from 15 to 20 per cent of the weevil larvae in fallen squares in

November

at Beeville

and Kenedy

weredestroyed

by

parasites. There is a bare possibilitythat in the original

home

of the weevil (south Mexico

and some

Central

American

States,aswellas certain of the

West

Indies)

more

efficaciousparasites could be lonnd, but this possibility is hardly sufficiently strong to warrantthe expenseof a search expedition.

REMEDIES.

Ill considering thematter of remedies

we must

start with the state-

ment

that experiencehas

shown

that noneof the general applications of insecticideswillbe^oftheslightestvalue againstthis species. There are measures, however, which cotton planters

may

adopt

and

which, if carriedout generallyat the right time,will postpone the appearanceof

theinsectin injurious

numbers

for oneor

two

generations,evenifthey

willnotpreventan

undue

multiplicationofthespecies. These measures are directed againstthe over-wintered weevils

and

thelarvaeoftheiirst

generation, since

where

theinsecthas once

become numerous

nothing can be doneto save the crop frompractical destruction.

We

have noticed that the weevils first appear in spring

among

clusters of

young

squares on the

most

advanced cottonplants. This suggests thepossibilityof trapping these earliest beetles

by means

of a very few cotton plants especially

grown

for this purpose. These plants

must

be

grown

at convenient points,

must

be protectedfrom

frost,

and

forced

by

watering, sothatthey will branchout

and

acquire buds eveninadvance of thevolunteercotton.

The

weevilswhichissue fromhibernating quarterson the first

warm

dayswill beattractedto theseplantsat once,and canbeeasilycollected

and

killed, if the plants are

examined

daily until the cotton in thefields has

become

of

some

size. Itis not likely that this planwill appeal to theaveragecotton planter, but

we

are convinced that

much

good can be done

by

its gen- eraladoption.

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 jdants as

come up

^{in corn fields}

and

in

abandoned

fields which, the previous year, were plantedto cotton, cannot be too stronglyrecommended, forit is

amatterofobservation thattheshade afforded

by

the cornortherank- growing

weeds

which

come up

ⁱⁿ

abandoned

fields isespecially favor- ableto the developmentof theweevils.

While

the plants areyoung,

and where

labor is as cheap as it is in south Texas, a great deal ofgood can be accomplished

by

picking

and

burningthefallensquares,

and

ifthisisdone promptly a large

number

of theinsects willbe destroyed. It should bedoneat least twice, at intervals of threeweeks,during the period while the plants are small.

As

soonasthe plantsbegintobranchout,however,this

method

becomes impracticable, on accountofthedifficultyoffinding the squaresonthe ground.

The

idea of picking the affected bollsduring the cotton picking

was

suggested inthe firstedition ofthecircular. It

was

thought that the affected bollscould be so readily recognized that

many

thousands of theinsects couldbe destroyed

by

the cotton pickers

by

picking these affected bolls

and

carrying

them away

in a separate receptacle tobe burned.

The amount

of extra labor involved in this operation, how- ever, would be very considerable,

and

the affected bolls in

many

instances are not toberecognized at a glance.

Thesemeasures, asidefromthe lastone, together with earlyplanting and clean cultivation, compriseallthat can be doneto save the cropof 1896. It is obvious, however, thatnogeneral adoption ol these simple measureswill be brought about this year,

and

that the probabilities are strong that theinsect will be quite as injurious as in 1895,if not

more

so.

A

good first crop will probably be secured if the climatic conditions arefavorable, butthetop crop^issuretobedestroyed bythe weevils. Thisdestruction,judgingfrom the experience ofthe past two years, will probably take place in September in mostof the localities

where

the weevils werepresent in1895,andat thistime the prospective loss of the top cropwill at once

become

evidentfrom the absenceof bloom.

7

The

prospectof

any

further picking of cotton being thus rendered so extremely small, a suggestion is obtained as to

what

^is perhaps, afterall,the mostpractical

way

of reducingthe

numbers

of the weevil and securing approximate

immunity

for the

summer

of 1897,

and

that is in the cutting

down and

burning of the plants at a time

when

it

becomes evident that the cotton yet tobe gathered will be very small in quantity. In

many

localities during the past

summer

this could have been done to very great advantage as earlyas thebeginningof October,

and

several large growers of cotton in Nueces

and Duval

counties

have

decided toundertakethis

means

nextyear.

The

success of thismeasure will naturally

depend upon

uniformity ofaction

among

the plantersof agiven region,

and

the difficultyof securing this uni- formity isthe

main argument

to be used against it.

Only

about halt the cotton in

Duval

County, for example, seems to be

grown by

the proprietors of the land; the remainder is

grown by

renters,

who

will

be not at all disposed to cut

down

their plants so long as a chance remains of picking a handful of cotton. In this

way

the plants in

many

fields will doubtless be left standing until toward the end of December.

Could anything like uniformity be secured, either

by

legislation or otherwise, ^itisinthis fall destruction of the cotton that onr besthope

lies atthe present outlook;

and

in this connection the further sugges- tionshould be

made

that notall the plants in

any

given fieldshould be destroyed in this way. All the insects which are in thelarval

and

pupal condition willbe destroyed

when

the cotton is burned, butthose which

may

beinthebeetlestagewill,

by

flight,escapealive. If,there- fore, a certain

Lumber

ofthe plants are left standing in everyfield,

these plants will attract the remaining beetles,which will settle

upon

them,sothatthey

may

readilybecollected

day

after

day and

destroyed.

If the plants are all cut

down and

burned, the beetles will spread far

and

wide; but if a few are left standing in thisway, the weevilswill concentrate

upon them

in such a

way

thattheycan be easilyhandled.

Where

there is obviously acertain

amount

of cotton still to be gath- ered after the earlypart

of

October,it

may

be an object to postpone thiscutting

down and

burningof theplants.

We have

foundthat the weevil continuestobreed

and may

be found in the bolls in all stages

up

to the time of the first frost

The

cutting

and

burning will then accomplish a considerable

amount

of good,evenif done during

Novem-

ber,although October would befar better.

From

thepresentoutlook, therefore, the best hope which the cotton plantersinthe affectedregionwill haveforthe futurewillbein follow- ing this last-described

method

in thefall of 180G,

and

the

more

thor- oughly

and

uniformly(and,in fact,theearlier)this isdonein

any

given locality the greaterwill be the chance for a good crop the following year. Unfortunately, aftertalkingwith

many

cotton planters in this region,

we

are

by

no

means

sure that theplan will be at allgenerally followed,forthe reasons suggested above;

and

as the prospectsofthese planters themselves, as well as the owners of cotton plantations in adjoining regions as yet uninfested, will

depend

almostentirelyon the generaladoption of this planor

some

betteronewhich

may

yetbedis- covered, it becomes necessary to look forward to the enforcement of remedial

work

bylegislation.

Itwillbegreatlytothe interestofall growersofcottonintheprolific districtlyingtothe northeast of the region atpresentinfestedtourge the passageof anact during the session of 1896-97 which will bring abouttheenforcementof remedial

work

^{in 1897. This act}should pro-

8

vide for the appointmentof commissionersin each county

upon

the applicationof acertain

number

of the citizensof that county. These commissioners shouldbe

empowered

to enforce remedial work, tolevy penalties, or tohavethe

work

done bytheir

own

agents,thecost tobe assessed

upon

the property? it will bewell to letthislaw haveawide bearing

and

not toconfine its applicationto 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 remaininoperative foryears, its application

would

be available in case of

any

sudden emergency, such as the introduction from a foreign countryofa

new

injurious insect, or thesuddenmulti- plication and spreadof

any

one of our nativespecies.

SUMMARY OF REMEDIES.

(1)Trapping over-wintered beetles

by means

of a fewearlyplanted cottouplants.

(2) Destruction of volunteer plantsin cornfieldsor

abandoned

fields.

(3) Picking fallen squares as fast as practicable, from the time the squares are formed ontheplant.

(4) Cutting

and

burningthe cotton stalks as early in thefallas prac- ticable, and,if possible, plowing the cotton fields atthe

same

time.

(5) Trapping the last weevils in the field

by means

of afew plants leftstanding.

There can be no doubt that this insect is the mostserious

enemy

to the cotton plant with which cotton growers in this country,have

had

to contend,

and

every effort should be

made

to prevent its further spread.

The

writerbelieves thatthis canbe accomplished, if,

by

con- certedaction oftheplanters,therecommendationsjust

made

arecarried outthroughouttheinfested region.

L. O.

Howard,

Entomologist.

Approved

:

Chas.

W. Dabney,

Jr.,

Assistant Secretary.

Washington,

1).

C,

February 12, 1896.