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CONTROL OF THE ARGENTINE ANT
IN ORANGE GROVES
J. R. HORTON
Scientific Assistant Tropical and Subtropical Fruit
Ins~, Investigations
FARMERS' BULLETIN 928
UNITED STATES DEPARTMENT OF AGRICULTURE
Contribution from the Bureau of Entomology
L. 0. HOWARD, Chief
Washington, D. C.
March, 1918
Show this bulletin to a neighbor. Additional copies may be obtained free from the
Division of Publications, United States Department of Agriculture
WASHINGTON : GOVERNMENT PRINTING OFFICE : 1918
SEVERAL VERY INJURIOUS scale pests of orange
would be much more largely controlled by their
insect enemies were it not for the Argentine ant.
This ant is very fond of the sweet substance,
known as honeydew, excreted by mealybugs and
other soft scales and is always very attentive to them
and prevents many of their insect enemies from ap-
proaching them. Thus the natural enemies of these
pests are hindered in carrying on their good work.
As a result, some of the soft scales become exces-
sively abundant.
The Argentine ant does not obtain honeydew from
the armored scales, but in patrolling the trees con-
stantly in large numbers in search of insect prey it
hinders, to a certain extent, the work of the natural
enemies of these scales, and if the control of the
scales be neglected for several seasons the infesta-
tion may be considerably increased.
In Louisiana orange groves this ant can be con-
trolled as an orchard and house pest by the trapping
method described on pages 12-17. Once the orchard
has been practically rid of ants, which can be done in
from 8 to 10 fumigations of the trapped ants, little
work will be needed to keep them from causing further
annoyance.
In California orange groves the ants can be pre-
vented from getting into the trees by banding the
trees in accordance with the instructions on pages
19-20, and their numbers can be reduced by poison-
ing. Recipes for ant poisons and directions for using
them are given on pages 17-19.
CONTROL OF THE ARGENTINE ANT1 IN ORANGE
GROVES.
CONTENTS.
Page. Page.
Introduction and importance ----- 3 The ant and the orange aphis --- 9
How the presence of the Argentine The ant and the citrus white fly__ 9
ant favors increased infestation by Prevention of injury to orange trees_ 10
scale insects ---___ ---- 4 Better orchard culture as a pre-
The ant and soft scales in Cali- ventive of injury in Louis-
fornia __---------- ----- 5 iana------------------- 10
The ant and soft scales in Lou- Trapping the ant in Louisiana_ 12
isiana -------------------- 7 Use of poisoned baits and ant
The ant and armored scales___ 8 barriers __---------------- 18
INTRODUCTION AND IMPORTANCE.
T HE ARGENTINE ANT was introduced first into the United
States on ships arriving at New Orleans from tropical Amer-
ican ports. It has been known in New Orleans for at least 25 years,
and probably has been reintroduced many times during that period.
It made its way from Orleans Parish into Plaquemines and St.
Bernard Parishes, along the lower Mississippi River, by rail and on
coal barges, and now occurs in slightly more than one-fourth of the
orange groves of Louisiana. It has become established widely in
California orange orchards, and is especially numerous in some
orchards in Los Angeles and Riverside Counties.
This ant is of first importance as a pest in houses, groceries, and
candy and meat shops. It not only causes great annoyance by per-
sistently getting into all foods containing sugar, fats, or fruit juices,
and into meat, but sometimes gets into beds and into the mouth and
nostrils of infants. It probably ranks near to the house fly as a
disease carrier, as it is a frequent visitor at feces and other sources
of infection and doubtless often nests in contaminated soil.
It has been rated as a very important pest of field and truck crops,
on certain of which it is said to cause great increase of mealybugs
and aphids. Sometimes it removes the seeds of certain kinds of
vegetables from the ground before they have germinated, necessitat-
1Iridomyrmer humilis Mayr.
FARMERS' BULLETIN 928.
ing resowing and protection of the seed. The ant also has been a
pest at times in greenhouses, where it occasionally cuts into certain
flowers and fosters mealybugs and aphids.
The general belief has been that in Louisiana the ant caused far
more serious damage to the orange trees than to any other crop. It
was thought to bring about a tremendous increase of all orange-
infesting scales, white flies, and aphids, to destroy the blossoms and
branches, injure the roots, greatly reduce the crop, and even kill the
trees. In reality the ant is responsible for only one form of direct
injury to orange trees. Rarely it chews into the petals and stamens
of open orange blossoms for the purpose of squeezing out the sap.
This occurs only on isolated trees, where food is scarce in compari-
son with the number of ants, and the amount of injury resulting is
unimportant except on rare occasions. The ants habitually visit
orange and other flowers to obtain nectar and to capture flower-
feeding insects, but ordinarily do no damage to the flowers. The
ant does not and can not injure sound oranges, although it enters
and feeds upon the juice of broken ripe or rotting fruits.
The chief importance of the Argentine ant in orange groves is due
to the fact that certain injurious scale insects become much more
abundant as a result of its presence, and that it fosters mealybugs and
aphids.
HOW THE PRESENCE OF THE ARGENTINE ANT FAVORS IN-
CREASED INFESTATION BY SCALE INSECTS.
Two very distinct groups, or classes, of scale insects infest orange
trees: (1) The armored scales, or those which settle permanently in a
particular spot, lose their legs, and form a protective covering, such
as a scale or shell, over the body. The eggs are deposited and the
young hatch under the protection of this shell. The hard, flattened,
apparently lifeless particles encrusting the branches and trunk and
sometimes the fruit and leaves of orange trees are the armored scales.
(2) The unarmored, or soft scales. These do not form a shell or
scale over the body nor do they lose entirely their legs and the power
of changing location. They are usually less flattened, softer, and,
when mature, in most cases larger than the armored scales. Certain
kinds, such as the mealybugs and the fluted scale, move about from
one location to another throughout their lives. Others, such as the
black, soft brown, and wax scales, usually settle down when partly
grown and remain in one spot, though they are able to move about
even in the later stages. The males of both classes of scale insects are
minute gnatlike insects with wings.
The relations of the Argentine ant with the soft scales and aphids
are direct and mutually beneficial. The ant is attracted to these
insects for their honeydew, a sweet liquid which it induces them to
CONTROL OF ARGENTINE ANT IN ORANGE GROVES.
excrete by stroking their bodies with its antennae, or feelers. The
honeydew of soft scales, aphids, and some other insects forms an
important part of the food of the ants. In securing this sweet excre-
tion the ants continually surround the scales and aphids and attack
any other insects that attempt to reach them. In this way they afford
considerable protection to the scale pests and make it possible for
certain species which have numerous and effective predacious enemies
to thrive and increase to the point of causing severe infestations.
The Argentine ant does not obtain honeydew from the armored
scales, but in patrolling the trees constantly in large numbers in search
of insect prey it hinders to a certain extent the work of the natural
enemies of these scales, and if the control of the scales is neglected for
several seasons the infestation is increased considerably.
Contrary to the general belief, the ant does not itself distribute
the scales and aphids of orange trees to start new colonies, although
an occasional ant is seen carrying living scales or aphids, or scale
shells, to the nest for flesh food and for nest construction. Of course,
wherever the abundance of scale insects has become greatly increased
through the presence of ants, a more rapid spread of the scales
through the usual agencies, such as winds, birds, etc., naturally
follows.
THE ANT AND SOFT SCALES IN CALIFORNIA.
Mealybugs.1-Infestations of mealybugs of the orange have been.
increased greatly in Los Angeles County, Cal., by the Argentine
ant. In this county the orange trees usually are kept free from other
scale insects and in vigorous health, and under these conditions,
when protected from their numerous predatory enemies by the ants,
the mealybugs are able to thrive. These natural enemies effect a
practical control of the mealybugs in many Los Angeles County
orange groves in the absence of the ant. As a result of the attend-
ance of the Argentine ant, infestations of three or four species of
mealybugs other than the common one are increasing in number and
severity, particularly in the Pasadena district.
Fluted scale.2-The fluted or cottony-cushion scale is almost, if
not quite, as eagerly sought and as closely attended by the Argentine
Dnt as are the mealybugs, owing, no doubt, to the large amount of
thick excretion which it supplies. At present, however, the ant can
not be said to cause the slightest injury to orange trees in California
through its relations with the fluted scale. Infestations of this scale
become as severe at times in some localities, whether the ant is present
or not, as when the insect was at the height of its abundance in earlier
1 Pseudococus citri (Risso) and other species of Pseudococcus.
2 Icerya purchsli Mask.
FARMERS' BULLETIN 928.
years. During 1916, however, the insect was very scarce, even in the
worst ant-infested orchards of Los Angeles, Riverside, and Ventura
Counties, there seldom being more than one or two scales per tree.
The chief factor in their control in California seems to be insect
enemies, chiefly the Australian lady-beetle,1 a parasitic fly,2 and lace-
winged insects; but there appears to be some other unknown factor
assisting.
Black scale.4-In California the black scale is rated as the most
important of all the citrus scales. It is generally held in check by
annual or biennial fumigation. Whether ants are in attendance or
not, infestation by this scale often becomes very severe and capable
of causing a heavy loss of crop after a single season in which fumiga-
tion has been neglected. Sometimes infestation is greater in trees
where there are no ants than in others of the same age and condition
overrun by ants. The black scale has quite a number of natural
enemies, including one or two intermittently effective internal para-
sites, but these enemies do not seem capable of keeping it under con-
trol; hence interference by the ant with the work of these enemies
does not accelerate greatly the increase of the scale.
Soft brown scale.5-The soft brown scale is a favorite of the Ar-
gentine ant. In Riverside County, Cal., this scale appears to have
increased considerably in certain ant-infested groves, especially
where for a long time fumigation has been neglected. Ordinarily it
is controlled along with other scales by fumigation and no special
treatment for the ant is needed. In Los Angeles and Ventura Coun-
ties both the soft brown scale and the closely allied citricola scale
are scarce in ant-invaded as well as in ant-free orchards. On more
isolated ornamental trees, bordering some of the streets of Pasadena
where the ants have become numerous, the scales are much more
numerous than where there are no ants.
The control of scales by fumigation in California makes it im-
probable that the ant will increase seriously the damage from the
black and soft brown scales in those orchards where fumigation is
conducted regularly, although annual fumigation may become neces-
sary in all groves invaded by the ants. The control of the mealy-
bugs will be facilitated greatly, and in many cases accomplished
fully, by the protection of the trees from ants. There are no present
indications that the ants will cause the fluted scale to become again
a menace to the State.
1 Novius cardinalis Muls.
2 Cryptochaetum monophlebi Skuse. (Identified by Frederick Knab.)
2 Chrysopa califorica Coq. and possibly others.
4 Saissetia oleae (Bern.).
5 Coccus hesperidum L.
6 Coccus citricola Campbell.
CONTROL OF ARGENTINE ANT IN ORANGE GROVES.
THE ANT AND SOFT SCALES IN LOUISIANA.
Mealybugs.-The ant has not had any such decided effect in in-
creasing the severity of mealybug infestation in the orange groves
of Louisiana as in those of California. The mealybugs usually start
to increase rapidly in some groves of Louisiana in the spring and
early summer and threaten to infest certain of them severely. But
at some time between June 15 and August 1 they are brought under
control by their natural enemies, regardless of the presence of the
ants. The common mealybug is at present held in check in the
Louisiana orange groves partly by its natural enemies, partly by the
overcrowding of the trees with armored scales and white flies, and
partly by the poor condition of the trees. The insect does not cause
the slightest damage to the orange trees, nor does it blemish the
fruit, under present conditions in Louisiana.
Fluted scale.-The fluted scale never yet has been found in the
orange groves of Louisiana, except in small and isolated plantings
on the Metairie Ridge. It therefore may be dismissed with the
citrus mealybugs as of no present importance as a cause of injury
to orange trees in Louisana.
Black scale.-Although the black scale occurs in parts of New
Orleans where the ants are most numerous, the ant has not yet caused
any great increase of infestation there, and this scale has not come to
the front as a pest, even of the ornamentals on which it occurs. It
does not appear to be present in the orange groves proper of
Louisiana. -.
Soft brown scale.-In the Louisiana orange groves the soft brown
scale appears and disappears, being kept in check mainly by its in-
ternal parasites, against which the ants are relatively ineffective.
The scales form in larger groups on occasional branches of an orange
tree when attended by the ants than in cases where there are no ants.
Occasionally trees are found having one or more small branches
heavily infested, but even where the ants are most numerous the trees
are not infested to a seriously injurious extent. The largest groups
of soft brown scales occur on food plants other than orange trees in
Louisiana.
From the foregoing it must be recognized that under present con-
ditions very little damage is done to the orange industry of Louisiana
by the Argentine ant through its relations with the unarmored, or
soft, scales. Only four of the six principal kinds of orange-infest-
ing soft scales occurring in this State have been found in the orange
groves proper. At least two of these four, namely, the Florida wax
scale2 and the barnacle scale,3 although attended by the ants, show
SPseudococcus citri (Risso).
2 Ceroplastes floridensis Comst.
8 Ceroplastes cirripediformis Comst.
FARMERS' BULLETIN 928.
no likelihood of ever becoming dangerously numerous. The fluted
scale may gain an entrance into the orange groves, and under ant
attendance and other favorable conditions may become a serious
menace. There is probably little to fear from the black scale under
the climatic and other conditions which obtain in Louisiana.
THE ANT AND ARMORED SCALES.
The armored scales do not excrete honeydew or any similar liquid
attractive to ants and, contrary to the general belief, are not attended
by ants. They probably would become the prey of the ants if it
were not for their protective shield, or scale. Ant shelters, or cow
sheds," sometimes occur over large and small groups of the armored
scales, but the number of scales covered is so exceedingly small that
it is unimportant. These shelters are erected for the protection of
the ants and not for the protection of the armored scales. The ant
does not disseminate any of the armored scales of citrus or colonize
them upon new growth or new trees.
The ants eat all insects that they can capture except those supply-
ing honeydew, and therefore they disturb certain enemies of the ar-
mored scales, and perhaps occasionally feed on the eggs of some of
them. It therefore may happen that after two or three years of
heavy and constant ant attendance, an orchard that is never sprayed
or fumigated for the control of the armored scales may become more
heavily infested by these scales than if ants were not present. Se-
vere and injurious scale infestations may develop in a single year, in
unsprayed orchards free from ants, as the natural enemies of the
scales are not effective control agents. The injury caused by these
scales, therefore, can not be prevented by destroying the ants. Direct
control measures against these scales must be adopted and persist-
ently practiced if orange growing is to be made profitable.
There are four important and destructive armored scales of orange
trees in Louisiana-the purple scale,1 chaff scale,2 long scale,8 and
white scale.' The purple and chaff scales are by far the most numer-
ous, generally distributed, and injurious, and for a long time have
been among the leading citrus pests of Louisiana. The infestations
of the armored scales are sometimes more severe where ants occur,
sometimes more so where they do not, and are almost certain to be
severe in untreated groves. These scales are more numerous on the
present-day budded orange trees of Louisiana than they ever were in
the seedling trees which formerly were common and which still are
grown in large numbers in Cameron Parish, but this is due to the
greater resistance of the seedling trees to scale infestation.
'Lepidosuphes b)eckii (Newm.).
SParlatoria pcrgandei Comist.
'Lepidosaphes gloverli (Pack.).
SChionaspis citri Comst.
CONTROL OF ARGENTINE ANT IN ORANGE GROVES.
The purple,1 rea, and yellow scales are the most important ar-
mored scales on citrus trees in California, but these usually are con-
trolled in this State by hydrocyanic-acid gas fumigation, the results
of which are not interfered with by the ants. Judging from present
information the ants do not appear to cause excessive infestations of
any of these scales in California.
THE ANT AND THE ORANGE APHIS.'
Notwithstanding the fact that the common aphis, or green louse,"
infesting orange trees appears to be desired less by the Argentine ant
than are the soft scales mentioned, it always is attended directly and
stroked by the ant for its honeydew. This aphis, furthermore, should
receive quite as much benefit as the armored scales from the mere oc-
currence of the ants upon the trees, but it suffers heavily from in-
ternal parasites, whereas scales do not. The ants are ineffective
against these little parasites, which often may be seen "stinging"
and depositing their eggs in aphids, even while attended by the ants.
The parasites are very small and active and nimbly avoid the ants.
The orange aphis becomes abundant on the tender growth in the
spring in both Louisiana and California, and often increases during
April and May, sometimes causing some of the leaves to curl. It dis-
appears rapidly, and numerous dried remains, each with a circular
hole through which a parasite has emerged, indicate the effectiveness
of these little enemies. The parasites are aided in the destruction
of aphids by certain lady-beetles, lacewings, and syrphus-fly larvae,
which are more or less immune to the attack of the ants. The. para-
sites, however, destroy a very large proportion of all the aphids, and
very effectively control them in ant-infested as well as all other
orange groves of California and Louisiana. The Argentine ant,
therefore, does not cause any important loss to the citrus industry
through the orange aphis.
THE ANT AND THE CITRUS WHITE FLY.5
The Argentine ant does not attend or obtain honeydew from the
citrus white fly. It is a direct enemy of this insect, the adults of
which it captures in large numbers during the principal emergence
periods. The ant sometimes is seen with immature stages of the
white fly in its jaws, but these are usually pupae from which the
adult insect is almost ready to emerge and which the ant im-
patiently has seized. A varying proportion of the emerging white
flies are captured by the ants, and in some cases for days at a time
1 Lepidosaphes beckii (Newm.). Aphis gossypii Glov.
SChrysomphalus aurantii (Mask.). 5 Dialeurodes citri (Ashm.).
3 hrysomplhalus citrinus (Coq.).
27818-18-Bull. 928--2
FARMERS' BULLETIN 928.
more than half of the foraging ants will be seen carrying these
insects down the trees.
The continuous patrolling of the trees by large numbers of ants
must have the same disturbing effect upon predatory insects which
may feed upon the white fly as upon those which prey upon the ar-
mored scales. Nevertheless, these enemies do not prevent extremely
heavy white-fly infestation in orchards where there are no ants,
whereas in groves in which ants are extremely numerous the amount
of white-fly infestation often is small.
PREVENTION OF INJURY TO ORANGE TREES.
In Louisiana the damage resulting to the orange industry from
the presence of the Argentine ant may be prevented largely by one
or more of the following measures: (1) General improvement in
orchard cultural practices, including the control of such orchard
pests as the armored scales, the white fly, and the rust mite. (2)
Direct measures for the destruction of the ant colonies and the use
of ant barriers.
In California the means of preventing injury and controlling the
ant are somewhat different. The armored scales are controlled by
standardized methods of fumigation; and other orchard practices
also are standardized to some extent. Banding, as described on
pages 19 and 20, to keep ants from ascending and descending the
trees, and poisoning (see pp. 17-19), appear to be the most promising
methods of control in that State.
BETTER ORCHARD CULTURE AS A PREVENTIVE OF INJURY IN LOUISIANA.
In Louisiana the first step toward preventing injury by the
Argentine ant should be the control of the armored scales, through
which most of this injury occurs, and the improvement of orchard
practices in general. The destruction of the ants will not remove
the necessity of controlling the armored scales and other principal
pests, nor will it prevent injury due to faulty cultural conditions.
Orange growing in Louisiana never has received the care and
attention that it merits, and it is capable of much greater com-
mercial development than it has yet attained. In the earlier days
citrus trees were grown there mostly for ornamental purposes or in
small yard plots supplying only enough fruit for home consumption.
Then followed small groves, almost exclusively of hardy seedling
varieties largely resistant to insect pests, the fruit from which repre-
sented almost clear gain, no money having been expended to grow
it, and the profits merely supplementing those from more important
sources.
1 See Farmers' Bulletin 923, Fumigation of Citrus Trees," which may be had free on
application to the Division of Publications, United States Department of Agriculture.
CONTROL OF ARGENTINE ANT IN ORANGE GROVES.
Most of the present plantings are budded trees set out since the
great freeze of 1899, which killed to the ground every orange tree in
the State. These trees are much more susceptible to injury from in-
sects and other natural influences encountered in Louisiana than are
the seedling trees. The nursery stock was largely of inferior quality,
and the trees usually were planted too close together in shallow, wet
soil, which encourages the roots to cover a great area close to the
surface. The insect pests were allowed to flourish unchecked, all cul-
tural care was neglected, and many of the trees were damaged fur-
ther by floods, storms, and freezing. As a result a large proportion
of them have remained undersized and in poor health. The amount
of production has never reached that of normal healthy trees, and at
from 7 to 10 years of age both trees and crop began to fail. The
maximum production of Louisiana orange trees was but slightly more
than three-fourths of a box per bearing tree, and the present produc-
tion is only about one-half of a box per tree.
The success of certain well-tended orange groves in Louisiana
demonstrates that oranges can be grown with profit in the State.
The only commercially successful and profitable groves, however, have
been those which receive an amount of care and attention much above
the average for the State. The Argentine ant now occurs in slightly
more than one-fourth of the Louisiana orange groves.
Comparison of the condition of the trees and the amount of the
crop in ant-invaded groves with those in groves in which there are no
ants shows that only about one-sixth more of the trees of the former
are in poor condition than of the latter, while the average reduction
in crop is only about one-fifth greater per tree in ant-invaded groves.
This difference probably is due largely to the greater neglect of ant-
infested trees because of discouragement at the invasion of the ant.
There are, of course, a number of groves in Louisiana that con-
sist of trees of such poor quality and in such a run-down condition
that they will never repay the cost of reclamation. There are others,
however, that can be so improved by spraying, cultivation, and
pruning that the production will be more than doubled in a single
season and still further increased by continued treatment.
In Louisiana, therefore, the improvement of cultural conditions
and the control of the armored scales, white fly, and rust mite, the
principal injurious pests, are absolutely imperative if orange grow-
ing is to be made successful, even where the Argentine ant is not pres-
ent. These insects can be controlled, even with the ant present, by
following a properly arranged program of spraying,' and they can not
1 For effective insecticides and directions for spraying, see Farmers' Bulletin 933.
" Spraying for the Control of Insects and Mites Attacking Citrus Trees in Florida,"
which may be obtained free from the Division of Publications, United States Department
of Agriculture.
FARMERS BULLETIN 928.
be controlled by the destruction of the ant alone. Presence of the
ants will not interfere with the control of these pests by spraying.
TRAPPING THE ANT IN LOUISIANA.
In Louisiana, owing to heavy annual rainfall, the ant colonies can
be collected in specially constructed traps and destroyed, a thorough
control thus being effected at moderate expense. Moreover, if this
method be followed diligently, permanent control, which at the same
time will eliminate the ant as a household pest, will be achieved.
This is by far the best and most practicable means of destroy-
ing the Argentine ant in the orange groves of Louisiana.' It
is the only method
adapted to ant de-
struction in large
groves and can be
used equally well in
house lots. The trap-
ping method of de-
struction is based on
the fact that the ants
can be induced to
concentrate in popu-
lous colonies in arti-
ficial nests to avoid
rain and can there be
conveniently killed
by fumigation. The
trap box meets every
nesting requirement
of the ant under
Louisiana condi-
tions. Not only are
rains and cold ex-
cluded, but to a large
extent draughts and
light also. Larger
Numbers of ants will
mass together in nu-
li'(;. 1.-Average killing of Argentine ants in ant trap used merous small colo-
in Louisiana orange groves. nies than in a few
1 The discovery that the ants would nest in large numbers in boxes of decaying vegetation
in winter was first made by Messrs. Newell and Barber, who describe a method of destroy-
ing them based on this fact. (See U. S. Dept. Agr. Bur. Ent. Bul. 122, p. 95-96.) The
trapping method described in the present bulletin depends upon the nesting of numerous
small colonies, that is, colonies averaging only from 100 to 160 queens each, in a
specially devised trap box which excludes rain.
CONTROL OF ARGENTINE ANT IN ORANGE GROVES.
extremely large ones. The traps are therefore small and a rather
large number per acre are used. An average-size mass of ants
killed in one of these traps is illustrated in figure 1.
CONSTRUCTION AND COST OF TRAPS AND FUMIGATING COVERS.
The trap (figs. 2 and 3, A) is made of --inch sap pine and con-
sists of the following nine pieces:
Two sides 12 by 12 inches.
Two sides 10 by 12 inches.
One bottom 10 by 10 inches.
Two top pieces 8 by 12 inches.
Two pieces triangular molding 12 inches long.
First the smaller sides and bottom are fastened together, then the
larger sides added. Rosined nails or screws should be used in order
to prevent separation at the seams and resultant enlargement of the
box to a size too great for the fumigation cover. The top pieces are
fastened together in the form of a gable with a tight joint, this roof
merely resting, loose, upon the top of the box to exclude rain. The
pieces of molding are
nailed across the in-
ner sides of the roof
to hold it in place.
A cover to keep the
gas in while fumigat-
ing is made of 28-
gauge galvanized
iron, consisting of one
piece 38 by 13~ inches,
bent into two right
angles, forming two
sides and the top, and
two pieces 131 by 13-
inches, forming the
other two sides. The
edges of the latter two
pieces are folded over
those of the first piece
and hammered tightly
together. Covers with
hammered seams are
suitable if very well
made, but soldered Fic. 2.-Trap used in destroying the Argentine ant in the
seams are to be pre- Louisiana orange groves. (Note.-There should be only
feared, although they a single hole in the bottom to connect with the ant
galleries under the trap.)
may be slightly more
expensive. The completed cover (fig. 3, B) should measure 121 by
121 inches inside, after a margin of one-fourth inch has been turned
down all around the edge to reinforce it.
FARMERS' BULLETT1 928.
The cost of the traps, based cn the price paid for 400 of them used
in experimental work in 1914, would be about 31 cents each. The
traps in question, made of C-grade sap pine, all parts cut to fit by the
milling company furnishing the lumber, were supplied knocked down
at 23 cents each, to which there was an additional charge of 8 cents
each for transportation and setting up. The cost of the fumigating
covers, based on the purchase of 48 of them in 1914, would be about
75 cents each, delivered.
PREPARING THE ORCHARD AND SETTING THE TRAPS.
The favorite rainy-weather nesting places of the ant are under
loose boards, boxes, logs, sacks, and other loose pieces of cloth, and
i'IG. 3.-Trap (A) and gas-tight cover (B) used in destroying the Argentine ant in
Louisiana orange groves,
in piles of lumber or bricks, dead weeds, etc. The ants also nest in
the walls of buildings when opportunity offers. They seek the
higher, better drained ground in wet weather, and usually the larger
colonies will be found on ditch banks and the high ground at the base
of the trees.
In order to induce more rapid concentration of the ant colonies in
the traps, the orchard as far as possible should be kept free from
suitable natural nesting places. It should be cleared of loose boards
and all similar materials under which the ants might collect. Piles
of dry weeds, cowpeas, and prunings from the orange trees should
not be allowed to collect in the grove, and stacks of lumber should
CONTROL OF ARGENTINE ANT IN ORANGE GROVES.
be set upon posts banded with the adhesive recommended on page 20,
to keep the ants out. The grove should be clean cultivated, from
March to September, by plowipg and disking both ways of the grove
three or four times during that period. Even the cover crops should
not be grown during the first season of trapping, or until a very large
part of the ants have been destroyed.
There should be at least 25 traps to the acre of 100 trees, and the
destruction of the ants will be accomplished much more rapidly if
twice that many are used. If 25 are used, one trap should be placed
near every other tree in each direction. For example, starting with
the first orchard row, set a trap near each of the first, third, and fifth
trees, etc., throughout the length' of the row, then similarly in the
third, fifth, and seventh rows, etc. The traps should be located just
under the outer spread of the trees, where they will not be in the
way of the cultivator or so close to the tree that it will be injured
by the carbon disulphid gas. At a distance of about 4 feet from the
trunk the trap still will be on the tree hill and there will be no
danger of injury to the tree from the fumigant. The trap should be
placed upon a slight, level elevation made by throwing up and
smoothing off a few shovelfuls of soil.
The number of covers necessary will depend upon the number of
traps and the conditions of labor. In experimental work with 415
traps, 48 covers could be operated most economically in fumigating,
as a crew of three could handle this number without loss of time
between setting and removing the covers. Therefore the proportion
of covers may be estimated roughly at 12 per 100 traps, or 3 per acre
of 25 traps, where 300 or 400 traps are used.
In winter the traps should be filled with damp but not wet stable
manure and dry weeds or straw, the manure occupying the lower half
of the box. In summer the manure, which is used principally for its
heat, may be omitted. Maggots of the house fly, and perhaps other
insects which inhabit the manure, serve as an added attraction to the
ants. It is important to keep the lids always on the traps, to keep
out rain and darken the nest, and to help retain its warmth in winter.
As rain is by far the most important factor in driving the ants into
the traps, many more ants will be destroyed by trapping in summer
than in winter.
METHOD AND COST OF FUMIGATING THE TRAPS.
When the traps are full of ants and ready for fumigation the lids
are removed, 2 fluid ounces of carbon disulphid poured in, and the
covers slipped on and banked with soil, one shovelful being tamped
down at each side to help retain the gas. The traps must be fumi-
gated for one hour. Two ounces of carbon disulphid per trap of 1
cubic foot capacity, for one hour, kills all stages of the ants in the
traps and for 3 inches in the ground beneath, as well as worms, sow-
bugs, etc., inhabiting the soil.
FARMERS' BULLETIN 928.
Once fumigation is started, it should be completed in 4 or 5- days,
or before possible dry weather may cause the ants to leave the traps.
If the number of traps is small, one man can conduct the fumigation,
but where there are 300 or 400 or more traps the work can be done
most efficiently by a crew of three, one to carry and measure the
insecticide while the other two remove and reset the covers and bank
with soil. Such a crew, working continuously, can handle 48 fumi-
gating covers, removing them from one lot of traps and placing them
over the next in from 50 minutes to one hour. Three men can
fumigate over 1,000 traps in 4 days.
The same trap filler may be used indefinitely, but it and the traps
must be aired thoroughly after each fumigation. The filler should
be spread out on the ground and the traps turned up to the sun for
several hours before resetting.
The cost of installing and operating the ant traps, based on the
prices prevailing in 1914-15, would probably run about as follows,
per acre of 100 trees:
25 traps at $0.31 each____----------------------------- $7. 75
3 covers at $0.75 each------------------------____-- 2.25
Net cost of traps and fumigating covers per acre------____ 10.00
In practice a crew of three have fumigated 400 traps in 11 8-hour
days; their services, at the rate of $1.25 per day each, cost $5.62. The
price of carbon disulphid prevailing in 1915 was $10.75 per hundred
pounds. On this basis the cost of fumigation, with the use of 25
traps per acre of 100 trees, would be about as follows:
Cost of labor, fumigating 25 traps at $0.014 each --------- $0.35
Cost of insecticide, 25 traps at $0.013 ench ______________ .325
Net cost of fumigation per acre------------------------- .675
From five to eight fumigations about one month apart will be
necessary to reduce the ants to an inconsiderable number in the
orange grove.
USE OF DRAINAGE DITCHES TO PREVENT REINFESTATION.
The orange grove will be rid of ants more rapidly if reinfestation
is prevented by means of barrier ditches. This means of preventing
the spread of ants is well known in Plaquemines Parish, where some
of the growers have adapted drainage ditches to this use. Where
drainage ditches already have been dug around three sides of the
orchard, as is the case in many orchards, they need only to be cleared
of weeds and provided with divided bridges which ants can not cross
(figs. 4 and 5) to adapt them for use against ants. On the lower land
subsurface water will remain in the ditches practically throughout
the rainy weather. In higher sections it will be necessary at times to
flood the ditches with water from the river by means of rice-irri-
CONTROL OF ARGENTINE ANT IN ORANGE GROVES.
gating siphons. The water can be siphoned over the levee in the
high-water stage, but must be forced over with gasoline engine and
pump during the low stage. The ants spread very little by flight, but
will travel far in the usual trails to nest in the traps, food usually
being plentiful in the orange trees near at hand.
COOPERAT1VIY AND COMMERCIAL TRAPPING.
By cooperative trapping, in which all the landowners in a given
section club together to purchase traps and insecticide, the ants can
be destroyed more thoroughly and rapidly than if each one should
undertake the work on his own account. Special crews could be
trained to carry on the fumigation efficiently, and the cost of the
FIG. 4.-A bridge which the Argentine ant can not cross. (Newell and Barber.)
traps and insecticide would be reduced by purchasing in large quan-
tity. The trapping method also might be put to use in southern
Louisiana by commercial concerns, which could undertake to rid the
land of ants at so much per acre.
USE OF POISONED BAITS' AND ANT BARRIERS.
POISONING THE ANTS.
Destruction of the Argentine ant by means of poisoned sirups and
other baits in orchards where orange trees, weeds, and windbreaks or
SFor a discussion of the control of the Argentine ant in the household, the reader is
referred to Bulletin No. 377 of the United States Department of Agriculture, "The
Argentine Ant: Distribution and Control in the United States."
FARMERS' BULLETIN 928.
borders of ornamental plants are left accessible to the ants is too slow
and uncertain to be of practical value. Under such circumstances
only a small proportion of the ants will be attracted from the natural
sources of food in the trees and weeds, as they soon learn the in-
jurious nature of the poison and ignore it, while continuing to feed at
the usual near-by sources of supply.
It is absolutely necessary, therefore, if satisfactory results are to
be obtained by this method, that all sources of food other than the
poisoned bait be eliminated so far as possible. This involves clean
cultivation and the banding of all trees, orange and ornamental, with
a mixture that will keep the ants out. Tree-banding alone in some
cases will cause a large proportion of the ants to migrate to another
FIG. 5.-Bridges which the Argentine ants can not cross. (Newell and Barber.)
locality in search of food and, as long as maintained, will have the
desired effect of preventing injury to the trees from the ants.
Although the employment of poisoned baits in accordance with the
instructions given below often may prove practicable and effective
in ridding yards where there are comparatively few trees infested by
ants, this method can not be recommended for general orchard use in
Louisiana as a substitute for the trapping method.
In preparation for the poisoning work, the premises should be
first freed of weeds, long grass, vines, and other plants that can not
be banded to keep out ants and that harbor aphids and scale insects.
Then all the trees should be banded in accordance with the direc-
tions on page 19. The ant poison then should be distributed liberally
CONTROL OF ARGENTINE ANT IN (01ANGE GROVES.
about the premises, in containers that will keep out rain. One-pint
fruit jars, of the type illustrated in figure 6, are suitable for this
purpose. A single hole is punched in the center of the lid for the
admission of the ants. A piece of sponge is placed in each jar to
aid the ants in reaching the poison. Scrap or waste sponges suitable
for this purpose sell for about 25 cents per pound at drug stores,
and 1 pound of them will serve for a dozen or more jars. About
one-half pint of sirup will serve for each jar. The jars should be
laid on their sides, and occasionally shifted to a new position.
The best poison is prepared as follows: Make a sirup by stirring
8 pounds of granulated sugar in one-half gallon of cold water until
dissolved, making 11 gallons of sirup. Then add 4- ounces of chloral
FIG. 6.-Artificial ant nest and jars used in poisoning the ants.
hydrate crystals, previously dissolved in a small quantity of water,
and about one-half pound of strained honey. The honey will add
to the attractiveness of the sirup.
If chloral hydrate can not be obtained, arsenite of soda may be
substituted. Dissolve 62 grains of tartaric acid crystals in 31 pints
of water. Then add 8 pounds of granulated sugar and boil until
dissolved. Allow to cool. Dissolve about 200 grains of arsenite of
soda (or 172 grains of white arsenic) in one-half pint of hot water.
When cool add to the sirup. Then add from one-half to three-
fourths pound of strained honey. The tartaric acid prevents the
souring of the arsenical sirup, which the ants will take very slowly.
USE OF TREE-BANDING MIXTURES.
In Louisiana orange groves the extensive use of adhesive and
other repellent mixtures for banding tree trunks to keep out ants
20 FARMERS' BULLETIN 928.
is not recommended in view of the more positive method of destroy-
ing the ants by trapping. When used on a large scale, even the best
bands of this sort will need more or less frequent inspection and
renewal or respreading. Although the first cost of banding pos-
sibly might be less than that of installing traps, the cost of permanent
maintenance would exceed the cost of trapping, and under present
conditions would not be justified by the increased crop returns. Tree
banding would cost more in Louisiana than in California, as in most
cases an average of three bands would be required for every orange-
tree banded in Louisiana, owing to the growth habit of the trees.
Furthermore, such barriers do not reduce the ant population, and
therefore can not be considered a positive means of control. In
Louisiana, therefore, the chief use of these mixtures will be found
in protecting yard trees and beehives from the ant and in keeping
it out of food supplies, beds, etc., in the house.
The most effective adhesive type of banding mixture, determined
from much testing of various materials and combinations of them,
is composed of 1 part by weight of flowers of- sulphur to 6 parts of
commercial tree adhesive. All the lumps in the sulphur should ba
broken and the two ingredients mixed thoroughly together without
heating, a wooden paddle serving this purpose. The sulphur not
only keeps the adhesive soft, but also has a sufficiently repellent
effect upon the ants to prevent their bridging the bands with bits
of trash or their own bodies.
Bands of this material will remain effective in rainy, foggy, or
exceptionally dry weather for from three to five months, and in the
cool weather of fall and winter as long as the ants are able to forage
out of doors. If directly exposed to the sun for long periods, however,
the surface of the bands becomes hard enough for the ants to cross. The
bands, therefore, must be applied where the shade of the tree will
protect them. The trees must be pruned so that branches will not
touch the ground, and weeds must be prevented from touching the
tree above the bands and allowing the ants to cross. The mixture
should not be applied directly to the bark, as it would be absorbed
to some extent and in time might injure the tree. First the trunk
should be wrapped snugly with tire or hose-mending tape for a
space about 6 inches wide, and then the adhesive should be applied
over this in a band about 4 inches wide and one-fourth inch thick.
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