Citation
Toxic bait studies with the imported fire ant, Solenopsis saevissima richteri Forel

Material Information

Title:
Toxic bait studies with the imported fire ant, Solenopsis saevissima richteri Forel
Added title page title:
Solenopsis saevissima
Creator:
Lofgren, Clifford Swanson, 1925- ( Dissertant )
Blanton, F. S. ( Thesis advisor )
Gilbert, I. H. ( Reviewer )
Smith, Carroll N. ( Reviewer )
Walker, T. J. ( Reviewer )
Pierce, Lowe E. ( Reviewer )
Place of Publication:
Gainesville, Fla.
Publisher:
University of Florida
Publication Date:
Copyright Date:
1968
Language:
English
Physical Description:
x, 67 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Ants ( jstor )
Corn cobs ( jstor )
Fats ( jstor )
Fire ants ( jstor )
Food ( jstor )
Infestation ( jstor )
Insecticides ( jstor )
Soybeans ( jstor )
Test ranges ( jstor )
Toxicity ( jstor )
Dissertations, Academic -- Entomology and Nematology -- UF
Entomology and Nematology thesis Ph. D
Insect baits and repellents ( lcsh )
Solenopsis invicta -- Control ( lcsh )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Abstract:
Studies were conducted to develop a toxic bait to control the imported fire ant, Solenopsis saevissima richteri Forel. The investigations were designed to find effective, inexpensive food attractants and delayed action toxicants that permit distribution of the bait in the colony before the worker ants are killed. A search was also made for granular carriers for the food attractants and toxicants that would carry the bait through vegetation to the ground where the ants forage. Vegetable oils with iodine values of about 100 and saturated animal fats such as lard and tallow were the most attractive food materials found. In addition, they are good solvents for the toxicants, relatively inexpensive and readily available. Highly unsaturated vegetable oils are unattractive. Rancidity and hydrogenation cause a decrease in the acceptance of vegetable oils. The most effective toxicant found was mirex. It gave delayed kill (less than I5/0 mortality after 2^^- hours but at least SO'jo after 2 to 20 days) over a k)0-fold range of concentrations (0.0025-1.0-;^). In a bait transfer test in which large worker ants transferred bait to equal numbers of minor workers, it gave kill of the minor workers over a 10- fold range of concentrations. It was the only toxicant that gave kill of major workers when baits were transferred to them by minor workers. Although not highly absorptive, the most useful and practical carrier was corncob grits. Mineral carriers such as attapulgite clay react with food oils, causing them to set-up or harden. The best bait formulation tested consisted of corncob grits (85;;^) impregnated with soybean oil containing mirex at concentrations of 0.075^ to 0.3^. It gave excellent control of ants in small plot tests. It is readily applied with various types of granular application equipment and is easily packaged and stored. Aerial application of this bait at the rate of 12 l/2 pounds per acre to a 960-acre plot gave over 99^0 control of ant colonies. The bait is now used routinely in the Imported Fire Ant Eradication Program.
Thesis:
Thesis (Ph. D.)--University of Florida, 1968.
Bibliography:
Bibliography: leaves 63-65.
Additional Physical Form:
Also available on World Wide Web
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Clifford Swanson Lofgren.

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University of Florida
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University of Florida
Rights Management:
Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
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ABU5645 ( NOTIS )

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TOXIC BAIT STUDIES WITH THE IMPORTED
FIRE ANT,

SOLENOPSIS SAEVISSIMA RICHTERI
FOREL








By
CLIFFORD SWANSON LOFGREN


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY










UNIVERSITY OF FLORIDA
1968








AGRIw ;
CULTU RADo
LIBRA Y




















































UNIVERSITY OF FLORIDA


3 1262 08552 2711













ACKNOWLEDGEMENTS


The writer wishes to express his deep appreciation to the members

of his committee: Dr. F. S. Blanton, Dr. C. N. Smith, Dr. T. J. Walker,

Mr. I. H. Gilbert and Dr. E. Lowe Pierce.

He acknowledges the support of the Plant Pest Control Division,

Agricultural Research Service, United States Department of Agriculture,

under whose auspices the research was conducted. He especially thanks

Mr. C. H. Gaddis for his suggestions during the course of the investic;a-

tions and Mr. C. E. Stringer, Jr., Mr. F. J. Bartlett and Mr. W. A. Banks

for their assistance in various phases of the work.













TABLE OF CONTENTS


page

ACKNOWLEDGEMENTS ii

LIST OF TABLES vi

LIST OF FIGURES viii

ABSTRACT ix

INTRODUCTION 1

LITERATURE REVIEW 2

Importation and Spread of the Imported Fire Ant 2

Life History 2

Biology and Ecology 3

Economic Importance 5

Medical Importance 5

Feeding Habits 6

Control 7

Residual insecticides 7

Baits 8

SCOPE OF STUDIES 10

METHODS AND MATERIALS 11

Laboratory Tests 11

Source and maintenance of ants 11

Food acceptability test 11

Toxic bait test 12





METHODS AND MATERIALS (continued) pag

Field Tests 18

Individual colony tests 18

Control tests 22

Small plot design and counting procedures 22

Application procedures 25

Formulation procedures 25

Large scale aerial application procedures 26

RESULTS 27

Acceptability of 32 Commercially Available Fats and Oils 27

The Effect of Hydrogenation on the Acceptability of
Cottonseed Oil 29

The Acceptability of Rancid Fats 30

The Effect of the Addition of some Anti-oxidants to Once-
refined Soybean Oil on Its Acceptance by Imported Fire Ants 31

A Comparison of the Toxicity of 7 Bait Toxicants with 3
Different Test Methods: Continuous, Limited and Transfer
Feeding 32

Toxicity of 4 Toxicants in Peanut Oil When Transferred by
Major or Minor Workers to Workers of the Opposite Size 34

The Acceptability of Baits to Individual Imported Fire Ant
Colonies: An Evaluation of 14 Different Carriers for Oil
Baits 36

The Acceptability of Flour-Soybean Oil Bait Containing
Various Concentrations of 4 Toxicants to Individual
Imported Fire Ant Colonies 40

Control of Imported Fire Ants with Granular Baits
Containing the Toxicants Kepone or Mirex and Soybean Oil 41

A Comparison of 6 Fats and Oils as Food Attractants in Toxic
Baits for Imported Fire Ant Control 46

The Effectiveness of 4 Toxicants in Flour-Soybean Oil Bait
in Controlling Imported Fire Ants 47








RESULTS (continued)
page

The Effectiveness of 4 Toxicants in Corncob Grits-Soybean
Oil Baits for Controlling Natural Infestations of Import-
ed Fire Ants 48

The Effectiveness of Different Application Rates of Corncob
Grits-Soybean Oil-Mirex Bait 51

The Effect of Mirex Concentration and Application Rate on
Control of Imported Fire Ants with Granulated Mirex-
Soybean Oil Bait 52

Control of Imported Fire Ants Following Aerial Application
of Granular Mirex-Soybean Oil Bait to 960 Acres Near
Orange Grove, Mississippi 54

SUMMARY AND CONCLUSIONS 60

LITERATURE CITED 63

BIOGRAPHICAL SKETCH 66












LIST OF TABLES


Table page

1. The acceptability of some commercially available fats
and oils to imported fire ants. 28

2. The effect of hydrogenation on the acceptability of
cottonseed oil as a food to imported fire ants. 29

3. Acceptability of soybean oil of different degrees of
rancidity as food to imported fire ants. 31

4. The effect of the addition of 2 anti-oxidants to once-
refined soybean oil on its acceptance by imported
fire ants. 32

5. The effective delayed toxicity range of 7 bait toxicants
in peanut oil to imported fire ants as determined by
3 different test methods. 33

6. Imported fire ant bait transfer tests with various
toxicants in peanut oil. 36

7. The acceptability to imported fire ants of baits
consisting of various carriers impregnated with
vegetable oils. 39

8. The acceptability to imported fire ants of flour-
soybean oil baits containing different concentrations
of 4 toxicants. 41

9. Control of imported fire ants with various toxic bait
formulations consisting of porous carriers impregnated
with soybean oil containing the toxicants, Kepone or
mirex. 42

10. A comparison of 5 fats or oils with soybean oil as food
attractants in imported fire ant baits. 47

11. The effectiveness of 4 toxicants in flour-soybean oil
bait for controlling natural infestations of imported
fire ants. 48







LIST OF TABLES (continued)


Table page

12. The effectiveness of 4 toxicants in soybean oil-
corncob grits bait for controlling natural
infestations of imported fire ants. 50

13. The effectiveness of a bait composed of corncob grits
(85%) impregnated with soybean oil (14.925%) and
mirex (0.075%) when applied at different rates per
acre. 51

14. The effect of mirex concentration and application rate
on control of imported fire ants with granulated mirex-
soybean oil bait. 53

15. Control of imported fire ants with granular mirex-soybean
oil bait on subplots within a 960-acre test area near
Orange Grove, Mississippi. 57

16. Control of imported fire ants following aerial applica-
tion of granular mirex-soybean oil bait to a 960-acre
test area near Orange Grove, Mississippi. 59












LIST OF FIGURES



Figure page

1. Materials used in toxic bait tests -- carbon dioxide
anesthetization chamber, vacuum tube, flower pot
test chambers, bottles containing bait formulations
and bottle caps with cotton for offering toxic baits
to ants. 16

2. A series of toxic bait test chambers sitting on wet
peat moss. 16

3. Worker ants are placed in squares of grid pattern
printed on standard mimeograph paper. 21

4. After ants are placed in squares as shown in Figure 4,
a portion of paper is folded over the ants and they
are crushed with a photographic roller. 21

5. Dye that is forced out of the ants when they are
crushed appears as colored spots on the paper. 21

6. An imported fire ant infested pasture typical of
those used in small plot tests with toxic baits. 24

7. An aerial photograph of 960-acre test area near Orange
Grove, Mississippi, showing locations of subplots
and check plots used for evaluating effectiveness
of granulated mirex bait. 55


viii







Abstract of Dissertation Presented to the Graduate Council
in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy


TOXIC BAIT STUDIES WITH THE IMPORTED
FIRE ANT, SOLENOPSIS SAEVISSIMA RICHTERI
FOREL

By

Clifford Swanson Lofgren

March, 1968



Chairman: Dr. F. S. Blanton

Major Department: Ehtomology



Studies were conducted to develop a toxic bait to control the

imported fire ant, Solenopsis saevissima richteri Forel. The investiga-

tions were designed to find effective, inexpensive food attractants and

delayed action toxicants that permit distribution of the bait in the

colony before the worker ants are killed. A search was also made for

granular carriers for the food attractants and toxicants that would

carry the bait through vegetation to the ground where the ants forage.

Vegetable oils with iodine values of about 100 and saturated animal

fats such as lard and tallow were the most attractive food materials

found. In addition, they are good solvents for the toxicants, relative-

ly inexpensive and readily available. Highly unsaturated vegetable oils

are unattractive. Rancidity and hydrogenation cause a decrease in the

acceptance of vegetable oils.

The most effective toxicant found was mirex. It gave delayed kill

(less than 15% mortality after 24 hours but at least 90%o after 2 to 20

days) over a 400-fold range of concentrations (0.0025-1.0%). In a bait

ix






transfer test in which large worker ants transferred bait to equal

numbers of minor workers, it gave kill of the minor workers over a 10-

fold range of concentrations. It was the only toxicant that gave kill

of major workers when baits were transferred to them by minor workers.

Although not highly absorptive, the most useful and practical

carrier was corncob grits. Mineral carriers such as attapulgite clay

react with food oils, causing them to set-up or harden.

The best bait formulation tested consisted of corncob grits (85%)

impregnated with soybean oil containing mirex at concentrations of

0.075% to 0.3%. It gave excellent control of ants in small plot tests.

It is readily applied with various types of granular application equip-

ment and is easily packaged and stored. Aerial application of this bait

at the rate of 12 1/2 pounds per acre to a 960-acre plot gave over 99%

control of ant colonies. The bait is now used routinely in the

Imported Fire Ant Eradication Program.













INTRODUCTION


From the late 1950's up to the present time, one of the most

controversial insect pests in this country has been the imported fire

ant, Solenopsis saevissima richteri Forel. The bulk of this contro-

versy has swirled around the multi-million dollar program initiated in

1957 by the Federal government to eradicate this pest. Innumerable

articles have been written and speeches made regarding the justification

or feasibility of this program and the hazards associated with the

r'- residual insecticides used in the early stages of the eradication

campaign) The development of an effective toxic bait in the early

1960's alleviated much of the concern generated over the use of the

residual insecticides and the associated potential dangers to wild

life and man. Arguments continue, however, over the economic importance

of the imported fire ant. The research reported in this dissertation

is part of the extensive effort expended in developing the imported fire

ant toxic bait mentioned previously.










LITERATURE REVIEW


Importation and Spread of the Imported Fire Ant


The imported fire ant is native to South America, occurring

principally in northern Argentina and Uruguay (Wilson, 1953). Other

subspecies and related species occur throughout much of that continent.

It was first reported in the United States by H. P. Loding in 1929 in

U.S.D.A. Insect Survey Bulletin 9. Creighton (1930) noticed this ant in

Mobile in 1926 and stated that Mr. Loding had said they occurred on the

Mobile Bayfront in 1918. Since its introduction, which presumably

occurred with ballast unloaded from boats from South America, the species

has spread over an area encompassing about 100,000,000 acres in the

states of Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi,

North Carolina, South Carolina and Texas. Much of the early spread was

undoubtedly attributable to movement of intact colonies or fertile

queens with nursery stock from the Mobile area (Anonymous, 1958).

Federal and state quarantine restrictions have essentially eliminated

spread from this and most other man related sources since their institu-

tion in 1957. Natural spread during mating flights has probably accounted

for most of the spread since then.


Life History


(The life history of the imported fire ant is similar to that of many

other ant species (Anonymous, 1958). A colony starts with a fertile queen







after the nuptial flight. She removes her wings after alighting on the

ground and immediately begins excavating a brood chamber in the soil or

under some protective object. She starts to lay eggs within a few days,

and these hatch in 8 to 10 days. The young larvae are fed by the queen

from food reserves within her body. The larval stage normally lasts from

6 to 12 days, and the pupal stage from 9 to 16 days. The first adults

are known as minim workers because of their small size, which is the

result of the limited food available to them. The minim workers begin

foraging and take over the care of the brood. The imported fire ant is

a polymorphic species, and workers of various sizes can be found in the

colony after a few months. The time required for the colony to produce

alate forms varies, depending upon climatic conditions. Khan (1969) has

reported that in laboratory and field tests at Starkville, Mississippi,

about 270 days are required. Rhoades (19-:7), however, stated that his

field observations in northern Florida indicated a colony could produce

alates in 15 to 18 weeks. From these observations, the life cycle of an

imported fire ant colony, that is, the time from the start of a colony

by a fertile queen to the production of virgin alates capable of mating

flights, is 4 1/2 to 9 months,depending upon prevailing climatic and

ecological conditions.


Biology and Ecology


The imported fire ant is extremely adaptable, and once a colony is

established it can survive under a variety of ecological situations. In

South America, it occurs from sea level to altitudes in the Andes above

10,000 feet (Hays, 1958). In the United States, however, cold weather

has apparently slowed the northward spread of the species, and it has not






established itself north of Texas, southern Arkansas, Mississippi, Ala-

bama and North Carolina. Preferred locations for queens to establish

new colonies are well-drained, closely grazed pastures, ditch banks and

dikes, road shoulders and cropland (provided it is not cultivated after

the queens have established their brood chambers). Swamps and woods are

generally less favorable, but in areas subjected to imported fire ant

mating flights for many years, colonies can become established even in

these areas.

One of the most characteristic habits of the species is its tendency

to build nests which consist of mounds of dirt, honeycombed with small

tunnels or galleries (Anonymous, 1958). These mounds vary in size,

depending upon the age of the colony and the soil type. In clay soil,

some mounds may be 2 to 3 feet in height and 3 to 4 feet in diameter at

the base. The area under the mound is also honeycombed with tunnels,

some of which may reach a depth of 5 feet. The mound is the main center

of activity for the colony. The queen, the brood, alate males and queens

and a large portion of the workers are found in it. Characteristically,

the mound is covered with a hard crust of dirt. The ants leave the nest

through tunnels which extend for long distances just beneath the soil

surface. Any disturbance of the mound results in an outrush of large

numbers of workers which attempt to sting the disturbing object or

animal. Afterwards, the ants quickly carry off the exposed brood into

the undisturbed tunnels and usually repair the mound. Occasionally,

the ants will move the nest; the reasons for this are not known, but it

presumably is due to some undesirable disturbance, ecological or

physical factor or a response to some new food source.







Economic Importance


Since the advent of the Federally sponsored eradication program,

there has been an extensivee debate about the economic importance of the

imported fire ant) Early reports (Wilson and Eads, 1949; Anonymous, 1958)

indicated that the ants caused considerable damage to various crops (corn,

okra, cabbage, potatoes, nursery stock, etc.). (Damage in the Alabama

counties of Baldwin and Mobile during 1949 was estimated to exceed

$500,000.00.) More recent reports such as that of the Fire Ant Committee

of the Georgia Academy of Science (Bellinger et al., 1964) have challenged

the importance of the imported fire ant as an economic pest. The theory

has been advanced that the habits of the imported fire ant have changed

so that it no longer feeds extensively on crops. This conclusion ignores

completely the fact that early observations were made prior to the time

when chlorinated hydrocarbon insecticides became an integral part of

farming operations for control of a wide variety of pests. Many of

these insecticides are extremely toxic to imported fire ants. Incidental

observations by the author have shown that imported fire ants do feed

very readily on okra flowers and the roots of cabbage and corn seedlings

in fields where no insecticides have been applied\

There is little question that the imported fire ant is a nuisance

pest primarily because of its mound building activities and aggressive

stinging habits. (The economic importance of this depends on the reaction

of the people involved. Obviously, if the nuisance is sufficient to cause

a person to expend money to kill the ants, they are an economic pest.


Medical Importance


The imported fire ant is of medical importance because of its






stinging habit. A sting of the imported fire ant is very painful and is

accompanied by a strong itching sensation. The venom injected is a strong

necrotizing agent which destroys the cells in a small area around the

point of penetration. This results in the development of a sterile

pustule after about 24 hours. Because of extreme sensitivity to the

venom or an excessive number of stings, individuals may undergo anaphy-

lactic shock which can result in death (Adrouny et al.,1959; Caro et al.,

1957; Jung and Derbes, 1957). Of lesser importance but still of

considerable concern are secondary infections which can result if the

pustule is broken from scratching the affected area.


Feeding Habits


The imported fire ant is an omnivorous feeder. The list of live

plants and animals and products processed from them which are subject to

attack is extensive. The ants ingest all 3 major food categories;

carbohydrates, proteins and fats. Hays and Arant (1960) and Bartlett and

Lofgren (1961) gave long lists of foods which were accepted in laboratory

tests but concluded that vegetable and animal fats and oils were the

most preferred foods. In the field, worker ants have been observed

attacking and carrying back to the colony a wide variety of small arthro-

pods. Larger animals also may be attacked and killed. However, the

author's observations have indicated that this usually does not occur

unless the animals are in a weakened condition. Newborn animals are

very often subject to attack, and the ants feed on carcasses of large

animals that have died from other causes. Feeding on plants occurs and

seems to be most pronounced on seeds or germinating seeds and seedlings

(Wilson and Eads, 1949). Young or mature plants are not fed on to any




7

extent. One exception appears to be the flowers of okra plants. The

ants apparently feed on nectar or oils produced in the flowers. Feeding

on honeydew of aphids and mealybugs has been reported (Anonymous, 1958;

Green, 1967). The ants in some instances build "chimneys" or tunnels

along the stems of the plants and around the aphids. Although imported

fire ants are voracious feeders, the colony can withstand extended

periods of drought or flooding when foraging is extremely difficult or

impossible. <


Control


Residual Insecticides

CInsecticidal control of the imported fire ant until reently has

relied primarily on the chlorinated cyclodiene insecticides such as

chlordane, heptachlor, dieldrin and aldrin. Laboratory tests showing

the toxicity of these and over 300 other compounds have been reported by

Lofgren et al.(1964). (Early control efforts were directed toward killing

.-the ants in their individual mounds (Green, 1952; Coarsey, 1952). This

method never proved highly effective. Numerous worker ants were killed,

but -f- the queen was not killed) the survivors moved their colonies to
/
a new location. Broadcast treatments in which all the surface area was

treated were much more effective (Eden and Arant, 1949; Blake et al.,

1959). Dust, emulsion concentrate, granular and fertilizer-insecticide

formulations were tested. Dosages of 1 to 4 pounds per acre gave

residual control for 1 to 4 years depending upon the insecticide used.

When the Imported Fire Ant Eradication Program was initiated in

1957, the standard treatments adopted were 2 pounds per acre of hepta-

chlor or dieldrin as granular formulations. This procedure was later






changed to 2 applications of 1/4 pound per acre of granular heptachlor

applied at intervals of 3 to 6 months (Lofgren et al., 1961; Lofgren et

al.,1965). This was done to save on application costs and to reduce

undesirable residues and hazards to wild life. (Residual treatments are

not used in this program at the present time. However, for small areas

where residues are not a problem, these insecticides still provide the

best and longest control


Baits

Poison baits have been a favored approach to ant control for many

years. The first large scale use of baits was in conjunction with con-

trol of the Argentine ant, Iridomyrmex humilis Mayr in the early 1900's.

Barber (1916) developed a sweet bait containing tartaric acid as the

toxicant. Other baits for this species with sodium arsenite or thallium

sulfate as toxicants have been reported by Mallis (1954). Effectiveness

of the baits reportedly was dependent upon the worker ants feeding it to

the queen. The slow action of the toxicants permitted this to be done

without killing the worker ants prematurely.

Travis (1939) reported on studies with the native fire ant, Solenop-

sis geminata (F.),in which he tested syrup baits containing thallium

sulfate and thallium acetate. Neither formulation was consistently

effective in the field. Green (1952) tested a bait consisting of thal-

lium sulfate with corn meal and oil against the imported fire ant. It

worked effectively on captive colonies but was ineffective when scattered

around mounds in the field. studiess conducted by Hays and Arant (1960)

indicated that peanut butter and Keaone (decachlorooctahydro-1,3-4-

metheno-2H-cyclobuta [cd] pentalen-2-one) at a concentration of 0.125%

and packed in soda straws gave control of imported fire ants. i







At the same time, Bartlett and Lofgren (1961) tested a bait consisting

of peanut meal-peanut oil and Kepone (0.25%) which gave 95% control of

imported fire ants on small field plots after 16 weeks. They also

reported on a useful technique for determining the acceptability of

baits based on the incorporation of dye in the food. After the dyed

baits were exposed to ant colonies for 24 to 48 hours, 100 worker ants

from each colony were examined for the presence of dye. Tests with

several vegetable and animal oils showed that corn, cottonseed, peanut,

olive, fish, cod-liver and neat's-foot oils were very attractive (43" to

71% of workers contained dye after 24 hours). Tung oil was completely

unacceptable.












SCOPE OF THESE STUDIES


The studies discussed in this report were initiated to develop an

effective and safe bait which could be used in a large scale eradication

or control program. The 2 primary ingredients of an ant bait are (1)

a highly attractive food material that is cheap and readily available

and (2) a highly effective toxicant with a delayed toxic action so that

it may be distributed throughout the ant colony, and especially to the

queen, before the workers are killed. To be entirely practical, the

bait must be formulated in such a way that it can be distributed over

large acreages and be readily found by the ants. (Since the ants forage

primarily on the soil surface, a granular bait which passes through

vegetation is most desirable) Based on these requirements, experimental

procedures were developed or modified for the evaluation of foods,

toxicants and granular carriers in the laboratory and field, and

numerous series of tests were conducted with them.













METHODS AND MATERIALS


Laboratory Tests


Source and Maintenance of Ants

Attempts to rear colonies from newly mated queens or to maintain

captive field colonies in the laboratory for long periods of time

(over 2 3 months) were unsuccessful. For the food acceptability

tests, ant colonies were collected as needed, placed in large wash tubs

with soil and moved into a greenhouse. The ants were kept from escaping

either by placing the tubs in large shallow pans filled with water or

by dusting the inner sides of the tubs with talc. The colonies were fed

for a week or more before they were used in any tests. Food consisted

of insects, vegetable oils, dog food and 10% sucrose solution in water.

This feeding period was necessary to decrease the activity of the ants

and make them more selective in food preference. Colonies which con-

tinued to feed very avidly or very sparingly were discarded.

Ants for the bait toxicant tests were collected the same day the

tests were initiated and were not prefed. All ants were obtained from

field colonies located in or near Gulfport, Mississippi.


Food Acceptability Tests

The search for the most suitable food material was limited to fats

and oils. This was done primarily because prior research had indicated

this type of food was very acceptable, readily available and generally







not very expensive. In addition, fats and oils are easy to formulate

on granular carriers, they are good solvents for most insecticides and

their water repellency makes bait formulations containing them less apt

to be destroyed by rain or dew after application.

The test methods employed were the same as those described by

Lofgren et al.(1961). Essentially, they consisted of comparing the

feeding activity of the ants on each food with that on a standard

material (peanut oil). The fats and oils were applied to 1-inch-square

pieces of blotting paper and placed on pieces of aluminum foil on soil

in a tub containing an imported fire ant colony. After 5 minutes, the

ants feeding on the candidate material and the standard were counted.

The ants were then removed from the food, the position of the 2 foods

on the mound were reversed, and a second 5-minute test was conducted.

One or more tests with 8 replications each were made with each food

material. An acceptance ratio for each material was determined by

dividing the total number of ants feeding on the candidate material by

the total number feeding on the standard. Using this procedure, 4 series

of tests were conducted to determine (1) the acceptability of 32 commer-

cially available fats and oils, (2) the effect of hydrogenation on the

acceptability of cottonseed oil, (3) the acceptability of rancid oils

and (4) the effect of anti-oxidants on acceptability of fats and oils.


Toxic Bait Test

The need of a laboratory method for rapidly screening a large num-

ber of bait toxicants against imported fire ants became very evident in

early work with baits. Many test methods for evaluating bait toxicants

on other insects have been reported; however, these methods are primarily







designed to select insecticides which give a quick kill. The objective

of a test for selecting toxicants for use in baits against a colonial

insect, such as the imported fire ant, must be to detect insecticides

which are characterized by a delayed killing action. The reason is that

the foraging ants must not become alarmed by the presence of the toxicant

or be killed before the bait is brought back to the colony. Observations

in the field have shown that once the ants become aware that they have

taken a poisoned bait, they will usually cease feeding on it and move

the colony.

The following procedures were employed in the laboratory studies.

Small plastic flower pots, 42 mm in diameter at the base and 63 mm at the

top with an upright rim 16mm high were used as test chambers. The rim

formed a narrow ridge at its base inside the pot. There were 3 small

holes in the bottom. A layer about 1/4-inch thick of plaster of paris

mixed with cement (9:1 ratio) was poured over the bottom of the pot and

allowed to harden. When the pots were placed on wet peat moss, the

plaster of paris acted as a wick to draw up water and maintain a high

humidity, which was essential for the survival of the ants. The cement

was added to make a harder mixture which the ants could not tunnel

through for escape. The ants were confined in the containers by small

plate-glass discs with a diameter slightly less than that of the rim,

so that they rested on the ridge between the rim and the tapered portion

of the chamber. The insides of the pots were dusted lightly with talc.

The talc had to be used sparingly because ants are easily killed by it.

especially in the absence of moisture or if they are in a weakened condi-

tion.

In preparing the toxic bait, the candidate insecticides were







dissolved directly in the food material; i.e., either peanut oil or 10-

sucrose solution, depending upon the solubility of the chemical. The

bait was offered to the ants on cotton plugs in small vial lids. Worker

ants were collected with the aid of carbon dioxide and an aspirator and

placed in the test containers the afternoon of the day preceding the test.

This time interval permitted the ants to recover from the effects of the

carbon dioxide and to orientate themselves to the container before the

start of the test. Ants that died during this 24-hour period were

replaced with others similarly conditioned. Figures 1 2 illustrate

various aspects of these procedures.

As mentioned previously, the objective of the tests was to

determine whether a toxicant would give delayed toxicity. In these tests,

delayed toxicity was defined as less than 15% mortality after a 24-hour

exposure and more than 89% mortality at the end of the test period

(2 to 20 days). Three different test methods -- continuous feeding,

limited feeding and bait transfer -- were used.

In the continuous feeding procedure, ad libitum feeding by the ants

was permitted throughout the test period. Observations for dead ants

were made over a 20-day period. It was recognized that this test did not

differentiate between delayed toxicity, temporary repellency, fumigant

action, or accumulative toxicity during the prolonged feeding period.

In the limited feeding tests, the previously described procedure was

modified so that the ants were allowed access to the bait for the initial

24 hours of the test period,after which the toxic bait was removed, and

the ants were starved for 24 hours. The ants were then provided with

uncontaminated peanut oil as food for the remainder of the 20-day test

period. The limited exposure to the toxicant insured that any delayed





















Figure 1.--Materials used in toxic bait tests -- carbon dioxide
anesthetization chamber, vacuum tube, flower pot
test chambers; bottles containing bait formulations
and bottle caps with cotton for offering toxic baits
to ants.


























Figure 2.--A series of toxic bait test chambers sitting on wet
peat moss.







- l----


O -


5 v







toxicity exhibited was due to delayed action rather than accumulative

action.

Imported fire ants readily pass food from one individual to another.

The bait transfer technique was designed to determine how effectively

toxic baits are passed between the worker ants. Worker ants were

separated into 2 groups according to size. Major or minor worker ants

were fed bait for 24 hours and then transferred to a clean test chamber

containing unfed ants of the opposite size. This sizing procedure per-

mitted a determination of which ants had been pre-fed.

Two experiments were conducted with these methods to thoroughly

evaluate 7 promising toxicants. In the first experiment, the delayed

toxicity range for the 7 toxicants was determined by the continuous and

limited feeding tests, and the effective toxicity range was determined

in the bait transfer test. Two tests with 2 replications each were

conducted. Twenty worker ants were used in each replication in the

continuous and limited feeding tests. In the bait transfer test, 10

major workers transferred bait to 10 minor workers in each replication.

The major workers were kept with the minor workers throughout the test,

but mortality counts were made only on the minor workers. Cbservations

for mortality were made over a 20-day period. The concentrations of

each toxicant in the peanut oil are recorded in Table 1.

In the second experiment, 4 toxicants were evaluated with the bait

transfer test to (1) compare their toxicity when 20 ants were pre-fed and

allowed to feed 10 unfed ants and (2) determine differences in toxicity

to major workers and minor workers. The toxicant concentrations were

the same as in the previous test. The pre-fed ants were separated from

the unfed ants after 3 days. Observations for mortality were made over


a 31-day period.







The toxicants evaluated

Bayer 30911



Bayer 38920




Coumaphos



1-Fluoro-
chlordene


Hooker HRS-
1243




Kepone


Mirex


in these studies were:

Phosphonothioic acid, methyl-,
0,2,4-dichlorophenyl 0-methyl
ester

6,9-Methano-3H-2,4-benzodioxepin,
6,7,8,9,10,10-hexachloro-l,5,5a,
6,9,9a-hexahydro-3-methyl-, chlori-
nated to contain 70% total chlorine

Phosphorothioic acid, O,0-diethyl
ester, O-ester with 3-chloro-7-
hydroxy-4-methylcoumarin


4,7-Methanoindene, 4,5,6,7,8,8-hexa-
chloro-l-fluoro-3a,4,7,7a-tetrahydro-


1,2-Propanediol, 3-[(l,la,3,3a,4,5,5,5a,
5b,6-decachlorooctahydro-2-hydroxy-l,
3,4-metheno-2H-cyclobuta[cd]pentalen-
2-yl)oxy]-

1,3,4-Metheno-2H-cyclobuta[cd]pentalen-
2-one, decachlorooctahydro-

1,3,4-Metheno-2H-cyclobuta[cd]pentalene,
dodecachlorooctahydro-


Field Tests


Individual Colony Tests

The acceptability of toxic and non-toxic baits was determined with

individual imported fire ant colonies as an intermediate step between

laboratory studies and attempts to control ants on small plots. The

most useful procedure for this purpose was that described by Bartlett

and Lofgren (1961). With this test, oil baits were treated with Calco-

oil red or blue dye (0.25% by weight). One hundred grams of bait was

scattered around the base of each mound. After 24 hours, worker ants

were collected and examined for the presence of dye in the gut. This was

done by placing 100 randomly selected ants (killed with methylene chloride)







on a sheet of white paper on part of which a grid pattern of 100 1/4-inch

squares was printed. (Figure 3.) After the ants had been placed indivi-

dually within the squares, the paper was folded in half over the ants.

A photographic roller was rolled over the folded paper, crushing the ants

and forcing their gut contents onto the paper. If dye was present, it

appeared as a stain on the paper. (Figures 4 and 5.) The number of

stained squares was determined by viewing the paper over a light box.

All of the tests were run with ant colonies along roadsides where they

were readily accessible and adequate space between colonies was easily

attained. Six replicates were made with each bait.

This test was particularly useful because it gave a rapid indication

of the acceptability of a bait (as indicated by its actual ingestion)

with a minimum of effort. Although it was not done in these tests, the

procedure could be expanded so that the distribution of the bait to all

ant forms in the colony could be determined. A more accurate evaluation

could undoubtedly be attained with the use of a radioactive material

such as P32. This would, however, be at the sacrifice of speed and

efficiency because of the need for much greater care in handling the bait

and the treated ants.

Two series of experiments were conducted using these procedures.

In the first series, baits consisting of vegetable or animal oils and

fats in various carriers were evaluated. In the second, the repellency

of various concentrations of 4 of the most promising toxicants combined

with a soybean oil (40%)-white flour (60O) bait was determined. This

bait was used in combination with the toxicants because it is readily

and consistently accepted by ant colonies in the field.














Figure 3.--Worker ants are placed in squares of grid pattern printed
on standard mimeograph paper.

















Figure 4.--After ants are placed in squares as shown in Figure 4, a
portion of paper is folded over the ants, and they are
crushed with a photographic roller.

















Figure 5.--Dye that is forced out of the ants when they are crushed
appears as colored spots on the paper.





21







Control tests

Small plot design and counting procedures.--Considerable difficulty

was encountered in obtaining a good evaluation of a bait in preliminary

field tests when 1-acre plots were used because of cross feeding by the

ants from one treated plot into another or because of early reinfestation

by colonies from adjacent untreated land or from plots where poor control

was obtained. To minimize these problems, the tests were conducted on

plots of 6 to 8 acres each. Three 1-acre subplots were set up within

the large plots. The subplots were at least 50 feet from each other and

from the border of the large plot. Only one large plot was treated with

each formulation. All of the plots were located in pastures. Figure 6

shows an imported fire ant infested pasture typical of those used in the

tests. The control obtained with each bait was determined by the percent

reduction in active imported fire ant mounds on the subplots at intervals

after treatment. An ant mound was considered active as long as more than

20 worker ants could be found, or if a wingless queen was found with less

than 20 workers. This was done to eliminate from the counts mounds con-

taining small numbers of worker ants, which are often found in old mounds

that have been abandoned. Mounds in which only alate males or females

remained were considered inactive. De-alated queens found alone were

assumed to be from post-treatment mating flights.

At the 16- or 26-week counts, incipient colonies were occasionally

found which indicated reinfestation from mating flights. Since these

colonies were not present at the time of treatment, they were excluded

from the total number of active colonies on the plot. This was done so

that the results of the tests would reflect only the effect of the baits

on the ant population present at the time of treatment. Only those


































Figure 6. An imported fire ant infested pasture typical of those
used in small plot tests with toxic baits.









































































































































V."i







colonies with very small mounds and a predominance of minor workers were

excluded.

Application procedures.--Cyclone hand seeders or power-take-off

Cyclone seeders mounted on jeeps were employed for distributing granular

baits in the early tests. In later tests, in which the corncob grits

carrier was used exclusively, the baits were distributed with a jeep-

mounted Buffalo turbine blower. The standard slurry (flour and soybean

oil) bait was applied with a specially designed applicator which pumped

the bait out each end of a 10-foot boom and dropped it directly to the

ground in strips 10 feet apart. With the exception of the bran baits,

the granular formulations were distributed uniformly over the entire

plot (30-foot swath with Buffalo turbine and 20-foot swath with the

Cyclone seeder). The bran baits were applied in 4-foot strips at 20-

foot intervals across the plot. Slurry baits were applied at the rate

of 6 pounds per acre; rates for the granular formulations varied and are

indicated in the table of results for the various tests.

Formulation procedures.-- The bait formulations were prepared by

pouring the oils over the granules or flour as they were mixed in a large

commercial electric food mixer. Because of the viscosity of the oils,

they do not readily penetrate porous carriers. This was overcome by

heating the oils to 1000 150C before application to the carriers.

With this procedure, it was in most instances possible, within the

carrier's absorptive limits, to obtain dry flowable formulations. In the

tests in which barriers were evaluated, the concentration of toxicant in

the formulations was based on the weight of the oil in the bait rather

than total formulation weight.

In the tests in which different carriers were compared and in some







of the bait toxicant evaluations, the standard bait consisted of 40,) soy-

bean oil and 60% white flour. Kepone at a concentration of 0.25% in the

oil was added to this bait.

Large scale aerial application procedures.--A 960-acre block of

land near Orange Grove, Mississippi, was selected for an aerial applica-

tion test with granulated mirex bait. It included varying types of land

cover and terrain. Approximately 50% of the area was in woodland, idle

or waste land. The remaining area consisted of small pastures, culti-

vated fields, gardens and pecan and tung groves. Thirty-three small plots

were set up within the area for making the pre- and post-treatment counts

for ant colonies. The size of these plots ranged from about 1/2 to 1 1/2

acres with the majority slightly under 1 acre. The pre-treatment count

of fire ant colonies per plot ranged from 7 to 43.

The bait formulation consisted of 0.075% mirex, 14.925% crude

soybean oil and 85% 10-40 mesh corncob grits and was prepared by a

commercial formulator. It was applied at the rate of 12 1/2 pounds per

acre (4.2 gms of mirex per acre) with a Piper Pawnee airplane equipped

with a Texas A & M type granular distributor. The overall swath width

obtained with the distributor was 60 feet; however, the actual swath

width flown with the plane was 30 feet. This was done to insure an

adequate overlap of the swaths, and it also permitted the operation of

the plane under higher wind conditions than would have been possible

with a narrower overlap of swaths. The swaths were marked by a man

stationed at each end of the plot holding specially designed balloons

covered with nylon covers and filled with helium. These are manufactured

commercially under the name, Kytoon.












RESULTS


The Acceptability of 32 Commercially Available Fats and Oils


Thirty-two commercially available fats and oils were compared for

their attractiveness as foods to the imported fire ant. In addition,

2 different grades or samples of 5 of the materials (hog grease, lard,

linseed oil, soybean oil and beef tallow) were tested. Nineteen of the

fats or oils gave acceptance ratios as good as or better than the peanut

oil standard (>0.90). (See Table 1.) The most attractive fats were the

2 types of tallow and 1 of the 2 lard.samples. It is evident that the

acceptance ratio for any fat can vary considerably from sample to sample

as evidenced by the results with lard (0.97 and 1.75) and soybean oil

(16 samples of crude soybean oil ranged from 0.59 to 1.01; 38 samples of

once-refined soybean oil varied from 0.97 to 2.01). Variation in the

peanut oil standard was avoided by running all tests with oil from the

same sample. The sample was stored in a refrigerator to avoid rancidity.

The results with soybean oil also showed that a crude grade of fat is

not as acceptable as the refined. The least attractive oils were those

classified as drying oils which are highly unsaturated. Examples of this

type of oil are the following which had acceptance ratios ranging from

0.05 to 0.53: linseed oil (I.V. 170-204), oiticica oil (I.V. 139-155),

perilla oil (I.V. 193-208) and tung oil (I.V. 160-175). The iodine value

(I.V.) is a measure of the degree of unsaturation. Common edible oils

such as peanut and soybean oils have I.V.'s of about 100.






Table l.--The acceptability of some commercially available fats and oils
to imported fire ants.

Acceptance
Fat or oila No. of tests ratio
Vegetable
Almond, sweet 4 1.03
Apricot kernel 4 1.09
Avocado 2 0.71
Castor 6 .13
Chaulmoogra 2 .15
Coconut 3 .68
Corn 2 .92
Cottonseed 2 1.37
Linseed, raw 4 0.53
Linseed, sun thickened 2 .13
Oiticica 1 .05
Olive 2 1.01
Palm 1 1.15
Palm kernel 2 0.94
Peanut 1.00
Perilla 1 0.31
Poppyseed 2 1.26
Rapeseed 5 0.72
Ricebran, crude 4 .81
Safflower 3 1.01
Sesame 3 0.45
Soybean, crudeb 49 .78
Soybean, once refined 111 1.26
Tung 8 0.35
Wheat germ 4 1.05
Animal
Butter 4 0.57
Butter oil 1 1.05
Cod liver 2 1.47
Dogfish liver 1 0.47
Grease oil, hogd 2 1.29
Grease, hog, white 7 1.17
Grease, hog, yellow 8 1.21
Lard, Sample Af 4 1.75
Lard, Sample Bf 2 0.97
Neat's-foot 12 1.00
Tallow, beef, fancy 6 1.97
Tallow, beef, top white 3 1.80

a The exact grades of all the samples are not known; however, unless
otherwise indicated, they can be considered as refined.
b Sixteen different samples. Acceptance ratios ranged from 0.59 to 1.01.
c Thirty-eight different samples. Acceptance ratios ranged from 0.97 to
2.01.
d The lower melting fats obtained from hog grease.
e Yellow grease is obtained by rendering the darker colored parts of the
hog; white grease is rendered from the remaining parts.
f Commercial edible grades of hog fat.







The Effect of Hydrogenation on the
Acceptability of Cottonseed Oil


A solidified fat would be preferable in a bait to eliminate loss of

the fat to other absorptive surfaces and to deter leaching of the fat

during exposure to rains. One means to accomplish this is to hydro-

genate the fat, thus decreasing its degree of unsaturation. A study was

therefore made to determine the effect of hydrogenation on the acceptabi-

lity of cottonseed oil. The samples of hydrogenated cottonseed oil were

prepared by Dr. T. H. Hopper, Chief, Industrial Crops Laboratory,

Southern Utilization Laboratory, Agricultural Research Service, United

States Department of Agriculture, New Orleans, Louisiana. Nine samples

with varying iodine values were prepared. The results (see Table 2)

show that as the degree of hydrogenation increases (I.V. 88.1 to I.V.

27.7) the acceptance ratio decreases (0.76 to 0.14).


Table 2.--The effect of hydrogenation on the acceptability of cottonseed
oil as a food to imported fire ants.a

Degree of hydrogenation as
indicated by iodine number Acceptance ratio

88.1 0.76
79.9 .75
72.7 .56
63.9 .42
53.7 .32
47.7 .24
39.7 .22
33.8 -12
27.7 .14


a Average results from 2 tests with 8 replications each.







The Acceptability of Rancid Fats


With reference to man, rancidity refers to any objectionable odor

or taste which develops in fats over a period of time. The principal

chemical changes which occur are a result of hydrolysis or oxidation.

They can be brought about by heat, light, moisture, air, enzymes,

bacteria and metals. During the chemical changes, free fatty acids,

ketones, peroxides and other substances are formed. The method used for

assessing the degree of rancidity in these tests involved the determina-

tion of a peroxide value. This value refers to the oxygen content in

milliequivalents per kg of fat sample and is a direct representation of

the amount of oxidized fat.

A sample of rancid soybean oil with a peroxide value of 600 was com-

pared with nonrancid soybean oil with a peroxide value of 2 for

acceptability to imported fire ants. The average acceptance ratio for

the rancid oil was 0.37 (5 tests) compared with 0.87 for the nonrancid

oil (6 tests). In a second experiment, the acceptability of 4 rancid

oil samples that had been extracted with pentane from soybean oil-

corncob grits baits was determined. These baits had been exposed to

normal weather conditions outdoors until the oil reached various stages

of rancidity. It is evident from the results (Table 3) that rancid oil

is much less attractive to imported fire ants. The acceptance values

for rancid oils were inversely proportional to the peroxide values for

every sample of oil tested.







Table 3.--Acceptability of soybean oil of different degrees of rancidity
as food to imported fire ants.a
Rancidity of oil as indicated
by peroxide value Acceptance ratio

33 1.42
191 0.41
215 .16
224 .13


a Average of 2 tests with 8 replications each.



The Effect of the Addition of some Anti-oxidants to
Once-refined Soybean Oil on Its Acceptance by Imported Fire Ants


Anti-oxidants are chemicals which delay the development of rancidi-

ty in fats. As a result, a test was conducted to determine the effect

of the addition of various concentrations of 2 anti-oxidants to refined

soybean oil on its acceptance by imported fire ants. The 2 anti-

oxidants, which were obtained from the Eastman Chemical Company, were

Tenox 7 butylatedd hydroxyanisole 28%, propyl gallate 12%, citric acid

6%, glyceryl monooleate 20%, propylene glycol 34%), and Tenox S-1

propyll gallate 20%, citric acid 10%, propylene glycol 70%). They were

tested at the concentration of 0.05, 0.1, 0.25 and 0.5% in the oil.

Sixteen replications were made with each. The results are presented in

Table 4.

None of the concentrations of the anti-oxidants appreciably

affected the acceptability of the soybean oil in these tests although

the acceptance ratios were still a little below that of the standard

(1.39). At the highest anti-oxidant concentration, 0.5%, the acceptance

ratios were 0.92 and 0.93. The results suggest that either of these

materials could be used in oil baits to preserve them during storage;







however, tests were not conducted with aged baits to determine if they

actually would retard rancidity without loss of attractiveness.



Table 4.--The effect of the addition of 2 anti-oxidants to once-refined
soybean oil on its acceptance by imported fire ants.

Anti- Cone. Avg. no. of ants Acceptance
oxidants (M) feeding on standard ratio

Tenox 7 0.05 62 1.17
0.1 63 1.02a
0.25 60 1.06
0.5 77 0.92
Tenox S-1 0.05 64 1.07
0.1 60 1.26
0.25 58 1.04
0.5 47 0.93
(Check)b 80 1.39


a Average of 24 replications; all other 16 replications.
b Once-refined soybean oil without anti-oxidants.



A Comparison of the Toxicity of 7 Bait Toxicants with 3
Different Test Methods: Continuous, Limited and Transfer Feeding


Seven toxicants which had been selected in previous tests for their

delayed toxic action were compared by 3 different test methods. The

results of these tests are presented in Table 5. The results of screen-

ing tests with these and over 300 other compounds have been reported

previously by Lofgren et al.(1967). The data have been summarized, and

only the days required to obtain 15% and 903 kill are given. This was

done because the primary objective of the tests was to determine the

delayed toxicity range. Mirex gave delayed toxicity in the continuous

and limited feeding tests over a 400-fold dosage range (0.0025-1.0));

in the bait transfer test, the range was 10-fold (0.1-1.0o). Kepone and

HRS-1243 were about equal in effectiveness and exhibited delayed action







in the continuous feeding test over a 50- to 100-fold dosage range and

in the limited feeding test over a 10- to 25-fold range. Neither com-

pound gave any appreciable delayed kill in the bait transfer test. The

remaining compounds gave delayed kill only in the continuous and limited

feeding tests and over a range which varied from 2- to 10-fold. In order

of effectiveness they were: Bayer 38920, coumaphos, Bayer 30911 and 1-

fluorochlordene.



Table 5.--The effective delayed toxicitya range of 7 bait toxicants in
peanut oil to imported fire ant workers as determined by 3
different test methods. (Corrected for check mortality by
Abbott's formula.)


Toxicant

Mirex


Cone.
()

0.001
.0025
.005
.01
.025
.05
.1
.25
.5
1.


HRS-1243 .005
.01
.025
.05
.1
.25
.5
1.


Kepone


.0025
.005
.01
.025
.05
.1
.25
.5
1.


Lethal time (days) required to kill 15o and 90%
of ants with each of the following test methods:
Continuous feeding Limited feeding Transfer feedingb
LT-15 LT-90 LT-15 LT-90 LT-15 LT-90


>20
17
13
11
7
7
4
4
3
3

>20
20
10
7
6
6
4
4

>20
20
15
8
8
8
4
6


>20
20
15
11
9
6
6
3
3
2

>20
20
9
7
7
4
4


>20
10
10
7
8
5


>20
>20
15
9
11
6


>20






Table 5.--Continued


Cone.
Toxicant (%)


Lethal time (days) required to kill 15', and 90,'
of ants with each of the following test methods:
Continuous feeding Limited feeding Transfer feeding
LT-15 LT-90 LT-15 LT-90 LT-15 LT-90


Bayer
38920







Coumaphos


>20
>20
15
13
8
8
5

>20
20
15
6
4


.001
.0025
.005
.01
.025
.05
.1

.001
.0025
.005
.01
.025
.05
.1


.001
.0025
.005
.01
.025

.0025
.005
.01
.025
.05
.1


>20 >20


>20
13
8
5


>20
20
7
3


>20



>20
>20
11
>20
15


>20
20
8
4


>20
11
3
2


>20


>20
>20
13




>20
>20
11

>20


>20
9
8
5


>20
10
6
4


1-Fluoro-
chlordene





Bayer 30911


Check


a Effective delayed
24 hours but at
b Ten minor workers


toxicity is defined as less
least 90% after 20 days.
fed by 10 major workers.


than 15% mortality after


Toxicity of 4 Toxicants in Peanut Oil When Transferred
by Major or Minor Workers to Workers of the Opposite Size


Four of the toxicants in the previous test were also evaluated in

bait transfer tests in which either major or minor workers were pre-fed;







the ratio of pre-fed to unfed workers was 2 to 1. The observations in

this experiment (see Table 6) were made over a 31-day period compared

to 20 days in the previous test. The results can be compared, however,

if the LT90 values of less than 21 days are considered. On this basis

all the toxicants with the exception of Bayer 30911 gave kill of the

minor workers over a greater range of dosages when the ratio of pre-

fed major workers to unfed minor workers was 2 to 1 than when it was 1

to 1 (see Table 5). The range was 100-fold for mirex, 40-fold for

HRS-1243, 4-fold for Kepone and 2-fold for Bayer 30911. The increased

toxicity was greater than would be theoretically expected. Presumably,

twice as much bait and toxicant was available to the minor workers and,

therefore, the lowest dosage causing mortality might drop by one-half.

Actually, it dropped by a factor of 4 to 10. Since field colonies were

used in these tests, the increased toxicity must be due to differences

such as the degree of hunger of the ants, body weight, or factors other

than numbers which would affect the quantity of bait actually transferred.

In the test where minor workers transferred bait to major workers,

only mirex was toxic enough to give kill over a range of dosages (0.1-

1.0%). This undoubtedly reflects a smaller uptake of bait by the minor

workers and a need for more toxicant to kill the major workers.






Table 6.--Imported fire ant bait transfer tests with various toxicants
in peanut oil.a

Days required to obtain indicated
kill:


Toxicant


Bayer 30911


10 minor workers
fed by 20 major
workers
15o 90%


Cone. (%)

0.005
.01
.025
.05
.1
.25
.5
1.0

0.01
.025
.05
.1
.25
.5
1.0

0.025
.05
.1
.25
.5
1.0


10 major workers
fed by 20 minor
workers
157 900


Mire::


>31-
21
17
11
11
10
6
4

>31
17
19
31
11
7
7

>31
>31
>31
12
8


>31
3-1
>31
31
28


>31 17


a Corrected for check mortality by Abbott's formula.



The Acceptability of Baits to Individual Imported Fire Ant
Colonies: An Evaluation of 14 Different Carriers for Oil Baits

A series of 5 tests was conducted to determine the acceptability of

baits consisting of 14 different granular carriers impregnated with


31
>31
>31
10
9
7
4
3

>31
>31
>31
>31
10
>31
>31

5
19
26
6
>31
>31

>31
>31
>31
11
>31


>31
>31
>31
31
28
28
14
13

>31
>31
>31
>31
31
>31
>31

>31
>31
>31
>31
>31
>31

>31
>31
>31
>31
>31

>31


HRS-1243


Kepone


0.005
.01
.025
.05
.1


Check







vegetable oils to imported fire ant colonies in the field. The various

baits evaluated, the composition of each and the results are recorded in

Table 7.

Acceptance of the standard white flour-soybean oil bait varied

from 40% to 75%. This variation probably reflects such differences as

temperature and availability of natural foods. Puffed barley grits,

aged pine sawdust, kenaf or okra hurds and corncob pith formulations

all gave results comparable to or better than the standard in their

respective tests. Wheat bran and corncob grits formulations were

slightly less attractive; however, it is believed this was a result of

a reduced amount of oil in these formulations. The fresh pine sawdust

formulation was definitely less attractive. The results with vermicu-

lite were erractic, and even at the highest oil concentration (75%), the

feeding rate was reduced 25% in comparison to tne standard. Feeding on

the clay granular formulations varied from 10% to 47% as compared to 75%

for the standard. All work with these carriers was discontinued when it

was found that the oils reacted with the granules and set up or hardened

within a few days to several weeks after formulation.

It was concluded from the tests and information on availability of

the carriers that puffed barley grits, wheat bran, aged pine sawdust and

corncob grits were the only carriers worthy of extensive field tests for

controlling imported fire ants.



















































Table 7.--Footnotes

a One hundred grams of bait scattered around each mound; six replica-
tions unless otherwise indicated. The mesh size range of the
granular carriers was as follows: puffed barley grits, 6-16;
corncob grits, 10-40; sawdust, minus 8; okra hurds, kenaf hurds
and corncob pith, 8-30; vermiculite and various clay granules,
20-40.
b The granulated stalk of this plant; kenaf is also called ambary,
Hibiscus cannabinus L.
c The granulated stalk of this plant.







Table 7.--The acceptability to imported fire ants of baits consisting of
various carriers impregnated with vegetable oils.a


Bait components


Oil and
Concentration


Carrier


Worker ants
containing
dye after
24 hours ( )


Test I


Peanut
Soybean
Cottonseed
Peanut
Soybean
Cottonseed
Soybean
Cottonseed
Soybean


Bran, wheat
Bran, wheat
Bran, wheat
Puffed barley
Puffed barley
Puffed barley
Corncob grits
Corncob grits
White flour


grits
grits
grits


Test II


Soybean


Soybean


Soybean


Sawdust, pine aged
Sawdust, pine, fresh
White flour

Test III

Kenaf hurdsb
Corncob pith
Okra hurdsc
White flour

Test IV

Vermiculite
Vermiculite
Vermiculite
Vermiculite
White flour

Test V

Pikes Peak 9J66
Creek-O-Nite
Attaclay AARVM
Florex ARVM
Pikes Peak 9I1LVM
White flour


Soybean







The Acceptability of Flour-Soybean Oil Bait Containing Various
Concentrations of 4 Toxicants to Individual Imported Fire Ant Colonies


In early field studies it was found that most insecticides exhibit

some degree of repellency when combined with a bait. As a result, tests

were conducted with 4 promising toxicants (mirex, Kepone, HRS-1243 and

Bayer 30911) to determine their effect on the acceptability of flour-

soybean oil baits. Various concentrations of the toxicants which

bracketed the upper levels of their toxicity range were tested. Feeding

activity was compared with that on the same bait without toxicant.

All the toxicants showed some repellency as the insecticide concen-

tration was increased (see Table 8). Mirex was definitely the least

repellent. The average number of ants containing dye at the 3 lowest

concentrations (0.05, 0.1 and 0.25%) was 84%. The acceptance decreased

to 64% at a concentration of 1%. The decrease in acceptance was very

pronounced with the other 3 compounds; the ranges in acceptance from the

lowest concentration to the highest were as follows: Kepone (80% to 25o),

HRS-1243 (83% to 28%) and Bayer 30911 (71% to 0%).

Some of the apparent repellency in these tests could be due to toxic

action of the insecticide; however, the insecticides were chosen because

of their delayed action, and general observations made during the test

did not reveal any appreciable number of dead ants around or in the test

colonies. As a result, toxicity was not considered to have any appreci-

able effect on the results.






Table 8.--The acceptability to imported fire ants of flour-soybean oil
baits containing different concentrations of 4 toxicants
Percent of ants containing dye at concentration (i)
indicated
Toxicant 0.025 0.05 0.1 0.125 0.25 0.5 1.0

Mirex 82 82 82 69 64
Kepone 79 74 53 48 25
HRS-1243 83 70 66 42 28
Bayer 30911 70 50 26 4 0 -


a Average of 6 replications. Acceptance of check containing no insecti-
cide was 94%.



Control of Imported Fire Ants With Granular Baits
Containing the Toxicants Kepone or Mirex and Soybean Oil


A series of 5 tests was conducted to evaluate wheat bran, corncob

grits, puffed barley grits and sawdust as carriers for toxic oil baits.

The results of the tests are presented in Table 9. In the first test,

the first 3 carriers were evaluated. The maximum amount of oil which

could be tolerated on the wheat bran and corncob grits was 15; without

their becoming too oily. Even at this low content, the bran, because of

its flat particles, would not flow readily and needed constant agitation

to maintain a flow through the hand seeders. The concentration of Kepone

in each of the baits was maintained at 0.25% on the basis of the weight

of the oil in the formulation. The puffed barley grits formulation gave

control comparable to that of the standard bait (981 and 97%) after

16 weeks. The corncob grits and bran baits gave 60% and 58% control,

respectively, after the same time interval; there was a 40% reduction

in the check plots.

Observations at the time of bait application in the first test showed

that the ants would quickly pick up and carry the bran and corncob grits













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baits to the colony. The poorer control obtained was attributed to the

small amount of oil and toxicant available per particle of bait. In

order to compensate for this, it appeared that either the oil content on

the carrier or the concentration of toxicant in the oil had to be in-

creased. The first of these alternatives was investigated in the second

test. Formulations of bran were prepared containing 15%, 20% and 25, by

weight of soybean oil. The concentration of Kepone in the oil in each

bait was 0.25%. Because of the extremely dense growth of grass on the

plots, it was impossible to make accurate counts of mounds at 8 to 16

weeks, so that final count was made after 26 weeks. The data show that

the speed of kill with the bait was directly proportional to the amount

of oil and toxicant in the bait; however, after 26 weeks, the percent

reduction in active mounds was comparable for the three formulations.

On the basis of these results, the third test was made to evaluate

the 3 carriers in the first test with modifications in the bran and

corncob grits formulations to compensate for the small amount of oil or

toxicant per particle of bait. Since no satisfactory method had been

found at this time to increase the amount of oil on the corncob grits

carrier, the Kepone concentration in the oil was increased to 0.5%.

It was found that bran-oil baits could be made containing 40% soy-

bean oil. This was done by adding 10% by weight of monoglycerides to the

soybean oil. The combination hardened on the bran, resulting in a formu-

lation comparable in oiliness to a 24% formulation without monoglycerides.

The puffed barley grits formulation remained the same with the exception

that 10% of monoglycerides was added to the oil to retard its seeping

from the grits when exposed to the hot sun during and after application

to the plots. With the exception of the corncob grits formulation, the







Kepone concentration in each bait was maintained at 0.25% of the weight

of the oil. The control data (Table 9, Test III) show that all of the

baits, including the standard as formulated in this test, gave complete

control of the ants.

About the time the previous test (No. III) was completed, mirex was

found to be a good toxicant. It was decided to shift emphasis to this

compound because mirex was: (1) less toxic to mammals than Kepone,

(2) not repellent to ants at high concentrations in the bait, and (3) a

little more toxic than Kepone but with good delayed toxic action.

Test IV was started to determine the effectiveness of mirex in the

soybean oil-corncob grits bait. Concentrations of 0.25% and 0.5% in the

oil were tested. The results show that, as with Kepone in the previous

experiment, complete control was obtained in 2 weeks at the 0.5' concen-

tration. At the 0.25% toxicant level, complete control was attained also;

however, the kill was very much delayed, and the maximum reduction was

not reached until after 8 weeks.

Test V was initiated to (1) evaluate sawdust as a carrier, (2) retest

the corncob grits formulation which had worked so well in the previous

experiments, and (3) determine the effectiveness of a corncob grits-

soybean oil formulation where the oiliness which occurred at oil levels

above 15% was overcome by coating the impregnated granules with gelatin.

Two levels of mirex in soybean oil (0.25% and 0.5%) were tested with the

sawdust carrier. The source of the sundried pine sawdust was an aban-

doned millsite near Gulfport, Mississippi. It was sieved through 1/0-

inch hardware cloth before formulation. The corncob grits-gelatin

formulation was prepared by pouring a hot 10% gelatin-water solution over

the oil-impregnated grits as they were tumbled in the mixer. The amount







of gelatin solution added was 12 1/2% by weight of the corncob grits and

oil. The concentration of mirex in the oil on both the corncob grits

formulations was 0.5%.

After 16 weeks, the control (see Table 9) obtained with the sawdust

formulations was 100% with the 0.25% mirex concentration and 97% with the

0.5%. The corncob grits formulation with the gelatin coating gave

slightly better control than the formulation without gelatin (97% vs. 91%

at 16 weeks).

In evaluating the 4 carriers tested on the basis of the criteria

listed in the introduction, it was evident that the corncob grits formu-

lations were the most satisfactory with regard to cost, formulation, ease

of handling, and ease of application with various types of conventional

application equipment.



A Comparison of 6 Fats and Oils as Food Attrac-ants
in Toxic Baits for Imported Fire Ant Control


Peanut oil, tallow, tallow oil, yellow hog grease, and hog grease

oil were compared with soybean oil as food attractants when used on corn-

cob grits with the toxicant mirex (0.5% in oil). The application rates

were 10 pounds per acre. The results are presented in Table 10. After

16 weeks, all the baits had given 100% control except the formulation with

yellow hog grease which gave 97/ control.




47


Table 10.--A comparison of 5 fats or oils with soybean oil as food attrac-
tants in imported fire ant baits. (All baits were made with
corncob grits as the carrier and contained 0.075% mirex in the
finished formulation).


Fat or oil

Soybean oil
Beef tallow oila
Beef tallowb
Yellow hog grease
Hog grease oild
Peanut oil
Check


Average pre-treatment count
of active mounds

13
10
10
12
13
33
12


Percent reduction in
active mounds after
weeks shown:
2 4 6 16

100 100 97 100
100 97 100 100
100 100 93 100
97 97 97 97
86 oo00 00 100
66 93 97 100
0 0 0 3


a Obtained from inedible tallow "stearine" by graining and
b Inedible No. 1 grade.
c An inedible fat obtained by rendering the darker-colored
hog.
d The lower melting fats obtained from grease.


pressing.

parts of the


The Effectiveness of 4 Toxicants in Flour-Soybean
Oil Bait in Controlling Imported Fire Ants


Kepone, mirex, HRS-1243 and Bayer 30911 were compared in white flour-

soybean oil baits for their effectiveness in controlling natural infesta-

tions of imported fire ants at various concentrations in the finished

formulation. The results (see Table 11) show that the most effective

toxicant was mirex. It gave 100% kill of the ants at both concentrations

tested (0.05% and 0.1%). HRS-1243 gave complete control at the highest

concentration (0.25%) and 99% at the lowest concentration (0.l )).

Bayer 30911 killed all the ants at a concentration of 0.05% in the bait

but produced a reduction of only 89% at the 0.02% concentration. The

decline of control after 16 weeks in Test I and 8 weeks in Test II was

from reinfestation from mating flights either just prior to or just after

the bait was applied. This count was made in September when new

colonies begin to build mounds with the onset of cooler weather.




48


Table 11.--The effectiveness of 4 toxicants in flour-soybean oil bait
for controlling natural infestations of imported fire ants.a
Percent reduction in
Avg. pre-treatment active mounds after
Toxicant and concentration count of active ant following weeks:
(;j) in finished formulation mounds 2 4 8 16
Test I

Mirex, 0.05 31 93 100 100 99
Mirex, 0.1 15 100 100 100 96
IRS-1243, 0.1 16 87 94 99 0
HRS-1243, 0.25 14 97 100 100 0
Kepone, 0.25 11 96 100 98 8
Check 14 13 5 5 0

Test II

Bayer 30911, 0.02 18 62 89 55 -
Bayer 30911, 0.05 15 98 100 85
Kepone, 0.25 14 83 100 00 -
Check 11 40 27 8 -


a Actual bait composition with white flour 56 or 50), soybean oil 43 or
47%, and monoglycerides 1 or 3%. Average results from three 1-acre
areas within 6-acre plot. Application rate 6 lb/acre.



The Effectiveness of 4 Toxicants in Corncob Grits-Soybean Oil
Baits for Controlling Natural Infestations of Imported Fire Ants


In a series of 3 tests, mirex, Kepone, HRS-1243 and Bayer 30911 were

evaluated in a corncob grits-soybean oil bait for control of imported

fire ants. The results are given in Table 12. In Test I, mirex was the

only toxicant which gave any appreciable amount of control (95% after 16

weeks). HRS-1243 gave a maximum control of 60% after 16 weeks. The

baits were applied in August; application was interrupted several times

by light showers. Since this bait will lose some of the oil and toxicant

when it comes in contact with water, the rain may have accounted for the

poor control obtained with all of the toxicants except mirex. The reason

for control with mirex can be attributed to its greater toxicity as

demonstrated in the laboratory tests.




49

In Test II, the plots started to become reinfested after 16 weeks

and in Test III, after 8 weeks. Both these counts were made in September,

at the time when incipient imported fire ant colonies are most easily

found. In addition, there was some migration in Test III of mature

colonies across the 50-foot buffer zone onto the count areas. For this

reason, the best evaluation of the results of these 2 tests can be made

by comparing the 2- to 8-week results in Test II with the 2- to 4-week

results in Test III. On this basis, Kepone and mirex at a concentration

of 0.075% both gave complete control. At the 0.15% level, however, mirex

gave 100% control in Test II and a high of 99% in Test III compared to

96%o and 99% respectively for Kepone. The lesser control by Kepone at the

highest concentration in Test II could be due to greater repellency at

this concentration (1% in the oil). HRS-1243 gave 95% and 97% control,

respectively, at concentrations of 0.15% and 0.3% in Test II and 99% con-

trol at the 0.3% level in Test III.













Table 12.--The effectiveness of 4 toxicants in soybean oil-corncob grits
bait for controlling natural infestations of imported fire
ants.


Conc.(Co) in
finished
formulation


Pre-treatment count in
active ant mounds


Percent reduction in
active mounds after
following weeks:
2 4 8 16


Test I


Bayer 30911

HRS-1243

Mirex
Check



Kepone

HRS-1243

Mirex

Check



Kepone

HRS-1243
Mirex

Check


0.015
.03
.075
.15
.075


Test II


0.075
.15
.15
.3
.075
.15


74
52
54
87
98
100
0


100
95
82
96
100
100
11


100
96
95
97
100
100
31


99
85
94
84
100
100
42


Test III


0.075
.15
.3
.075
.15


93
48b
73b
95
93
0


100
91
99
100
98
24


a Average results from 3 count areas in a 6-acre plot; application rate
10 lb/acre.
b These figures include mounds introduced into the area from mating
flights or migration subsequent to application of the toxic bait.


Toxicant





51

The Effectiveness of Different Application
Rates of Corncob Grits-Soybean Oil-Mirex Bait


Tests with the corncob grits (85/)-soybean oil(14.925%')-mirex(0.075%)

bait were conducted to determine its effectiveness at application rates

varying from 2 1/2 to 15 pounds per acre.

After 16 weeks, complete control was attained with application rates

of 5 pounds per acre and higher (see Table 13). Fair control (52%) re-

sulted from the 2 1/2-pound rate. Most of the colonies remaining on this

plot were affected, and the following spring only 2 colonies contained

brood at a time when colonies on the check plots contained an abundance

of brood.

The ant infestation in the pasture selected for the test ranged

from 13 to 36 mounds per acre. This number is about normal for southern

Mississippi. It is possible that higher numbers of colonies per acre

might have affected the degree of control at the 5- and 7 1/2-pound

rates. Other unreported tests have definitely shown that 10 to 15

pounds per acre is sufficient to control infestations as high as 100

mounds of normal size per acre.



Table 13.--The effectiveness of a bait composed of corncob grits (85i)
impregnated with soybean oil (14.925%) and mirex (0.075')
when applied at different rates per acre.
Percent reduction in
Average active mounds after
Dosage Grams of mirex pre-treatment count in following weeks:
(lb/acre) per acre active ant mounds 2 4 8 17

2.5 0.85 36 10 11 13 52
5.0 1.70 21 31 52 87 100
7.5 2.55 17 73 88 98 100
10.0 3.40 18 63 91 94 100
15.0 5.11 13 98 98 o10 100
Check 29 0 1 2 5







The Effect of Mirex Concentration and Application
Rate on Control of Imported Fire Ants With Granulated
Mirex-Soybean Oil Bait


A study was made to determine the effectiveness of granulated mirex-

soybean oil bait containing 0.075%, 0.154 or 0.3% mirex and applied at

the rate of 3, 5 or 10 pounds per acre. Two complete tests were conduct-

ed; one was started in March and the second in June. The results of the

pre- and post-treatment observations on the plots through 16 weeks are

presented in Table 14. No counts were made on any of the plots after

16 weeks, because they had become reinfested with new colonies. When

this happens, it becomes extremely difficult to distinguish between the

remnants of old colonies and the new ones. However, at the 16-week

observations, many of the remaining colonies showed symptoms characteris-

tic of toxic bait poisoning; that is, only large workers remained, total

worker population was below normal, the mounds were not worked, and no

brood was present. In all tests, records were kept of the number of

abnormal colonies present at each count period. Continued observation

of these colonies has shown that they almost always die. Because of this

fact, a percent reduction in active mounds for each treatment was calcu-

lated with the assumption that all abnormal colonies present after 16

weeks eventually died. Although this information has little relevancy

for small acreage control, it does indicate the potential result if a

similar treatment were applied over a large acreage in an eradication

program where mating flights into the area would not be a factor.

The data show that a very high degree of control of the ant popula-

tion present at treatment time was obtained on all the plots. There was

no distinct difference in control attributable to the 3 different mirex

concentrations and application rates with the possible exception of







0.075% mirex bait applied at 3 pounds per acre in March. However, even

with this treatment, if all the abnormal colonies died, the eventual

control would have been 98%. There was a marked difference in speed of

kill between the March and June treatments. This result was undoubtedly

due to temperature differences which have a marked effect on activity of

the ants.


Table 14.--The effect
control of


of mirex concentration and application rate on
imported fire ants with granulated mirex-soybean
oil bait.a


Formulation
application
rate (ib/acre)


Pre-treatment
count of
active ant
mounds


Percent reduction
in active mounds
after following
weeks:
2 4 8 16


Percent reduction
in active mounds
if all abnormal
colonies died


March Test

10 43
13 65
23 50
20 53
11 58
84 100
57 79
10 56
48 86

June Test


100
100
95
100
100
100
97
99
99


100
100
95
99
99
100
96
99
100


82
87
89
79
83
100
99
95
100


99
100
98
99
97
100
95
100
100


81
97
99
98
99
100
97
98
100


99
100
100
99
100
100
98
99
100


98.3
99.5
100
98.9
99.6
100
100
98.8
100


100
100
100
100
100
100
100
100
100


6- to 8-acre plot.


Mirex
Cone.
(%)


0.075


.15


.3


.075


.15


.3


a Average results from three 1-acre subplots within a
b See text for description of abnormal colonies.







Control of Imported Fire Ants Following Aerial Application
Of Granular Mirex-Soybean Oil Bait to 960 Acres
Near Orange Grove, Mississippi


The results of the preceding tests definitely show that the most

promising bait for large scale applications is the one consisting of

soybean oil, mirex and corncob grits. In all cases, it gave high or

complete control on small test plots. In addition, it proved amenable to

standard packaging, storage and application procedures. To be certain

of its effectiveness, however, it was necessary to test the bait over a

large area that included a variety of land cover and usage. In addition,

its safety to man and animals needed to be verified. To satisfy these

requirements, a large scale aerial application was made to a 1 1/2 square

mile block of land near Orange Grove, Mississippi. Figure 7 is an

aerial photograph of the area indicating the individual subplots where

pre- and post-treatment counts were taken. The bait was applied to the

area in September. Post-treatment observations for active colonies were

made over a 1-year period with the results for each subplot tabulated in

Table 15 and summarized in Table 16.

It is evident that the bait treatment was very effective in control-

ling imported fire ants. At the end of 32 weeks, 100% control had been

obtained in all the observation plots except one. On this plot, one

colony was found. This colony was not observed on the plot at the 26-

week count. It is not known whether this was a new colony which had

developed after treatment, or an old colony that had not been killed out.

It will be noted that the kill of ants was very slow and that even after

4 weeks, some of the plots showed no reduction in active ant mounds.

General observations showed that the greatest effect of the bait was

obtained 4 to 8 weeks after treatment. After abouc 5 weeks of extremely





















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dry weather following the application of the bait, thousands of dead ants

were found piled up in the road ditches surrounding the test area. The

slow kill is undoubtedly attributable to the fact that the test was

initiated at the onset of cool weather and to light feeding of the ants

on the bait. The light feeding was evidenced by the lack of piles of

bait around the ant mounds. Normally, when feeding activity is heavy,

small piles of bait from which the ants have extracted the oil are found

around the base of the mounds within several days after the bait applica-

tion. A rapid kill of ants is associated with this behavior.

Observations in the test area one year later, showed that it had

become heavily reinfested with small ant colonies with mounds ranging

from 2-4 inches in diameter. The number of these colonies found on the

plots ranged from 0 to 256. Heavy infestations of ants were present in

all the surrounding area,providing a ready source of new queens during

mating flights. This reinfestation pattern is typical of that noted on

small test plots and illustrates the fact that baits offer no residual

protection against reinfestation. In general, observations have shown

that areas treated with bait from January through July most likely will

become reinfested the next fall, while areas treated during the latter

part of the year will not become reinfested until the fall of the follow-

ing year. The actual reinfestation in either case appears to coincide

with the period of greatest mating flight activity (May-June). It cannot

be concluded from these observations that queens from mating flights late

in the year will never establish colonies; however, the percentage which

does successfully establish a colony is evidently very low. Green (1962)

has suggested that large outbreaks of new imported fire ant infestations

coincide with periods of frequent showers during June, July and August.







Table 15.--Control of imported fire ants with granular mirex-soybean oil
bait on subplots within a 960-acre test area near Orange Grove,
Mississippi.a

Pre-treatment Percent reduction in active
Plot count of active mounds after following weeks:
Land usage no. ant mounds 2 4 8 16 26 32 52

Treated Plots


Woods, heavy



Woods, light






Pecan grove,
pasture



Pecan grove,
cultivated

Pasture








Idle or
wasteland


0 0 32 91 100 100 77
56 44 67 00oo 00oo 00oo 00oo
7 7 57 71 79 100 100

0 35 85 100 oo 100oo o
44 64 81 loo00 oo00 oo00 0
19 43 90 100 100 00oo 95
25 5 70 80 95 100 90
8 o 75 83 00oo 00oo 92
12 0 65 82 100 100 100oo

36 50 94 97 94 loo 64
0 0 67 75 00oo loo
59 94 100 loo oo00 oo 0
36 80 96 oo00 oo00 100 0

75 92 100 100 100 100 -
21 42 89 97 100 97 0

26 58 84 o100 oo 1oo 48
53 49 88 98 loo loo 61
11 25 68 93 100 100 o
48 58 94 loo oo oo00 0
12 0 62 100 100 100 0
80 86 97 100 100 63
7 45 83 93 00oo ioo o
27 53 83 93 97 100 17


52 67 100 100 -
60 75 85 80 80 100 65
0 0 63 88 100 ioo o
33 50 oo 00oo 00oo 00oo 0
7 o 37 90 oo oo00 40
25 50 70 90 loo 1 oo 6o

15 o 62 100 100 0
43 43 71 100 100 0
42 58 83 92 loo 0
14 o 57 100 1oo 1oo 0


Cropland






Table 15.--Continued
Pre-treatment Percent reduction in active
Plot count of active mounds after following weeks:
Land usage no. ant mounds 2 4 8 16 26 32 52

Check Plots

Pasture 38 22 0 0 0 0 0 0 0
Woods 39 13 0 23 31 0 8 15 15
Wasteland 40 22 0 23 27 0 50 0
Cultivated 41 22 0 0 32 18b -
Corn field 42 10 0 30 0 20 80 40
Pecan grove 43 17 6 0 0 29 47 0
Woods, pasture 44 31 19 10 32 10 55 19


a Application of bait made by airplane on September 21-23, 1961; applica-
tion rate 12.5 lb/acre; bait consisted of 0.075% mirex; 14.925%
soybean oil, and 85% corncob grits.
b Plot was mound treated with insecticide by farmer; so counts were dis-
continued.



This indicates that warmth and moisture are essential for colony estab-

lishment. Green (1959) also noted that extremely cold weather can

result in mortality of imported fire ants. This was noted also in the

Gulfport, Mississippi, area when temperatures dropped to 10F during

January and December, 1962, and January, 1963. Large numbers of dead

ants could be found outside some mounds after the weather became warmer

and the live ants could remove the dead ones. Cold weather could be a

factor in reducing or eliminating development of colonies by queens from

mating flights late in the year.

Concurrent with this test, a study was made of the effects of the

bait on wild life; milk was obtained from cows grazing within the treated

area and vegetables were harvested and analyzed chemically for mirex

residues. No adverse effects to wild life were noted (Baker, 1963) and

no residues in milk or on the vegetables were found (Lofgren et al.,

1964). The analytical methods were accurate to 3 ppb in the milk

residue and 10 ppb in the vegetable studies.








Table 16.--Control of imported fire ants following aerial application of
granular mirex-soybean oil bait to a 960-acre test area near
Orange Grove, Mississippi.a


Average pre-
Number of treatment count
Land usage observation plots of active mounds

Woods 9 20
Pecan grove 4 23
Pasture 8 32
Idle 6 22
Crops 6 15


Percent reduction in
active mounds after
following weeks:
4 6 16 32 52

27 72 92 100 60
58 92 96 100 26
49 83 97 100 27
39 74 92 100 36
40 82 99 99 0


a A summary of results presented in Table 15.



Following these tests, mirex bait was tested on several large blocks

of land. One of these, near Savannah, Georgia, contained about 80,000

acres. Excellent control was obtained in all instances; however, rein-

festation patterns similar to those in the previous test were noted.

As indicated in the introduction to this dissertation, mirex bait is now

used routinely in the Imported Fire Ant Eradication Program.













SUMMARY AND CONCLUSIONS


The imported fire ant, Solenopsis saevissima richteri Forel, was

introduced into the southeastern part of the United States during the

early 1900's. It spread from the original infestation at Mobile,

Alabama, into 9 other states encompassing an area of about 100,000,000

acres. Although it causes little direct damage by feeding on plants, its

mound building and stinging habits make it an extreme nuisance to both

urban and rural dwellers. The research discussed in this dissertation

was conducted to develop a toxic bait which could be used for the control

or eradication of this pest. Studies were conducted with food attractants,

toxicants and granular carriers. The following conclusions are based

on the results attained:

1. Most animal and vegetable fats are readily accepted by imported

fire ants as food; highly unsaturated fats such as linseed oil, oiticica

oil, perilla oil and tung oil are much less attractive.

2. The cost and availability of soybean oil are factors which

make it preferable as the food attractant in baits for large scale con-

trol programs.

3. A once-refined grade of soybean oil is consistently more

attractive than a crude grade.

4. Hydrogenation of cottonseed oil showed that as the degree of

hydrogenation increases, acceptability to the ants decreases.

5. Rancidity causes fats to become less acceptable to ants.







6. Two anti-oxidants, Tenox 7 and Tenox S-1 did not appreciably

decrease the attractiveness of soybean oil at concentrations of 0.05 to

0.5%.

7. Mirex is an extremely effective bait toxicant. In continuous

and limited feeding tests, it gave delayed toxicity over a 400-fold

dosage range (0.0025-1.0%); in a bait transfer test where 10 major

workers were pre-fed and allowed to transfer food to 10 minor workers,

it produced toxicity over a 10-fold range (0.1-1.0%).

8. Kepone and HRS-1243 are also effective toxicants, giving de-

layed kill over a 10- to 25-fold range in limited feeding tests.

9. Bayer 38920, Bayer 30911, coumaphos and l-fluorochlordene gave

delayed kill of ants over a 2- to 10-fold dosage range.

10. In bait transfer fests where 20 major workers were allowed to

transfer bait to 10 minor workers, mirex killed over a 100-fold dosage

range; HRS-1243, a 40-fold range; Kepone, a 4-fold range; and Bayer

30911, a 2-fold range.

11. In laboratory tests where 20 minor workers transferred bait to

10 major workers, mirex was the only toxicant that satisfactorily killed

over a range of dosages (0.1-1.0%).

12. Puffed barley grits, aged pine sawdust, kenaf or okra hurds,

wheat bran and corncob pith or grits are satisfactory carriers for oil

baits on the basis of dyed food tests with individual imported fire ant

colonies; fresh pine sawdust, vermiculite and several mineral carriers

are unacceptable.

Q In dyed food tests with individual ant colonies, mirex was

less repellent than Kepone, HRS-1243 and Bayer 30911.

14. In tests on small field plots, baits consisting of soybean oil




62

containing mirex or Kepone and wheat bran, corncob grits, puffed barley

grits or aged pine sawdust gave control of imported fire ants.

15. On the basis of cost, availability, ease of formulation and

handling and ease of application with conventional application equipment,

the most practical carrier for the oil baits is corncob grits.

16. Soybean oil, beef tallow oil, beef tallow, yellow hog grease,

hog grease oil and peanut oil are all good food attractants in mirex-

corncob grits baits.

17. Mirex, Kepone and HRS-1243 were all highly effective as toxi-

cants in flour-soybean oil baits for controlling imported fire ants in

small plot field tests at dosages ranging from 0.05 to 0.25%; Bayer

30911 at 0.05% gave good control but only fair control at 0.02O.

18. Mirex and Kepone at concentrations of 0.075% and 0.15% in

soybean oil-corncob grits baits gave very good control of imported fire

ants in small field plots; HRS-1243 gave good control at a 0.3% concen-

tration but poor to fair control at concentrations of 0.075% and 0.15%.

19. Corncob grits-soybean oil bait containing 0.075% mirex gives

excellent control when applied at rates of 5 to 15 pounds per acre but

poor control at 2 1/2 pounds per acre.

20. Soybean oil-corncob grits baits containing 0.0755, 0.15; or

0.3/ of mirex and applied to field plots at rates of 3, 5 or 10 pounds

per acre give excellent control of imported fire ants; control of ants

is significantly faster when baits are applied during warm summer

weather.

21. Aerial application of corncob grits-soybean oil-mirex bait to

a 960-acre plot demonstrated that the bait effectively controlled ants

in woods, pecan groves, pasture, waste land and crop land (only one

colony out of 750 remained on 33 observation plots).













LITERATURE CITED


Adrouny, G. A., V. J. Derbes, and R. C. Jung. 1959. Isolation of a
hemolytic component of fire ant venom. Science 130(3373):449.

Anonymous 1958. Observations on the biology of the imported fire ant.
U.S.D.A. ARS 33-49.

Baker, M. F. 1963. New fire ant bait. Highlights of Agricultural
Research, Agr. Exp. Sta. of Auburn Univ. 10(2):16.

Barber, E. R. 1916. The Argentine Ant. Distribution and Control in
the United States. U.S.D.A. Bull. 377.

Bartlett, F. J., and C. S. Lofgren. 1961. Field studies with baits
against Solenopsis saevissima richteri, the imported fire ant.
J. Econ. Entomol. 54(1):70-73.

Bellinger, F., R. E. Dyer, R. King, and R. B. Platt. 1964. The
imported fire ant. A report by the Fire Ant Committee of the
Georgia Academy of Science, Inc. 46pp.

Blake, G. H., W. G. Eden, and K. L. Hays. 1959. Residual effectiveness
of chlorinated hydrocarbons for control of the imported fire ant.
J. Econ. Entomol. 52(1):1-3.

Caro, M. R., V. J. Derbes, and R. Jung. 1957. Skin responses to the
sting of the imported fire ant (Solenopsis saevissima). Arch.
Dermotol. 75(4):475-488.

Coarsey, J. M. 1952. Third quarterly report for 1952. Station,
Kerrville, Texas, Div. of Insects Affecting Man and Animals, Bur.
Ent. and Plant Quar., Agric. Res. Serv., U. S. Dept. Agric.

Creighton, W. S. 1930. The new world species of the genus Solenopsis
(Hymenop., Formicidae). Amer. Acad. Arts and Sci. Proc.
66(2):87-89.

Eden, W. G., and F. S. Arant. 1949. Control of the imported fire ant
in Alabama. J. Econ. Entomol. 42(6):976-979.

Green, H. B. 1952. Biology and control of the imported fire ant in
Mississippi. J. Econ. Entomol. 45(4):593-597.

Green, H. B. 1959. Imported fire ant mortality due to cold. J. Econ.
Entomol. 52(2):347.







Green, H. B. 1962. On the biology of the imported fire ant. J. Econ.
Entomol. 55(6):1003-1004.

Green, -. B. 1967. The imported fire ant in Mississippi. Miss. State
Univ. Agr. Exp. Sta. Bull. 737.

Hays, K. L. 1958. The present status of the imported fire ant in
Argentina. J. Econ. Entomol. 51(1):111-112.

Hays, S. B., and F. S. Arant. 1960. Insecticidal baits for control of
the imported fire ant, Solenopsis saevissima richteri. J. Econ.
Entomol. 53(2):188-191.

Jung, R. C., and V. J. Derbes. 1957. The imported fire ant, Solenopsis
saevissima var. richteri, as an agent of disease. Amer. J. Trop.
Med. and Hyg. 6(2):372-373.

Khan, A. R. 1966. Studies on the rearing, biology and control of the
imported fire ant. Dissertation State College, Mississippi, 91 pp.

Lofgren, C. S., V. E. Adler, and W. F. Barthel. 1961. Effect of some
variations in formulation or application procedure on control of the
imported fire ant with granular heptachlor. J. Econ. Entomol.
54(1):45-47.

Lofgren, C. S., W. A. Banks, and C. E. Stringer. 1964. Toxicity of
various insecticides to the imported fire ant. U.S.D.A. ARS 81-11.

Lofgren, C. S., F. J. Bartlett, and C. E. Stringer. 1961. Imported
fire ant toxic bait studies: the evaluation of various food
materials. J. Econ. Entomol. 54(6):1096-1100.

Lofgren, C. S., C. E. Stringer, W. A. Banks, and P. M. Bishop. 1967.
Laboratory tests with candidate bait toxicants against the imported
fire ant. U.S.D.A. ARS 81-14.

Lofgren, C. S., C. E. Stringer, Jr., F. J. Bartlett, W. A. Banks, and
W. F. Barthel. 1965. Dual low dosage applications of heptachlor
for control of the imported fire ant. Fla. Ent. 48(4):265-270.

Mallis, Arnold. 1954. Handbook of pest control. Second Edition.
New York. MacNair-Dorland Company. 1068p.

Rhoades, W. C., and D. R. Davis. 1967. Effects of meteorological
factors on the biology and control of the imported fire ant.
J. Econ. Entomol. 60(2):554-558.

Travis, B. V. 1939. Poisoned-bait tests against the fire ant, with
special reference to thallium sulfate and thallium acetate.
J. Econ. Entomol. 32(5):706-713.

Wilson, E. O. 1953. Origin of the variation in the imported fire ant.
Evolution 7(3):262-263.





65


Wilson, E. 0., and J. H. Eads. 1949. A report on the imported fire ant.
Solenopsis saevissima var. richteri Forel in Alabama. Ala. Dept.
of Conservation, Spec. Rpt. July 16.53pp. plus 13 plates, mimeo-
graphed.













BIOGRAPHICAL SKETCH


Clifford Swanson Lofgren was born July 29, 1925, in St. James,

Minnesota, where he lived and attended school until he entered the

United States Army in March, 1946. He worked as a Surgical Technician

in the Medical Corps until his discharge in August, 1947. The next

month, he enrolled at Gustavus Adolphus College, St. Peter, Minnesota.

He graduated in 1950 with a Bachelor of Arts degree with a major in

Chemistry. In 1951, he was accepted as a student in the Department of

Entomology and Economic Zoology of the University of Minnesota and re-

ceived the Master of Science degree in 1954. From 1954 to 1955, he was

employed by the Plant Pest Control Division of the Agricultural Research

Service of the United States Department of Agriculture on the Golden

Nematode Project at Hicksville, New York. In 1955, he transferred to

the Insects Affecting Man and Animals Laboratory of the Entomology Re-

search Division of the Agricultural Research Service of the United

States Department of Agriculture in Orlando, Florida, where he conducted

research on the control of household insects. In 1957, he was trans-

ferred to the Plant Pest Control Division at Gulfport, Mississippi, to

organize and direct a research program for developing methods of control

for the imported fire ant.

In 1963, he returned to the Insects Affecting Man and Animals

Laboratory, which had moved to Gainesville, Florida. Since then, he has

been Project Leader of the Area Control Section of the Laboratory, with




67


the responsibility of developing methods for outdoor control of mosqui-

toes, ticks, chiggers and other medically important arthropods.

Clifford Swanson Lofgren was married to the former Renee Kathleen

Liljenberg in 1954 and is the father of 3 children. He is a member of

the Entomological Society of America, the American Mosquito Control

Association, the Florida Entomological Society and the Florida Anti-

mosquito Association.
















This dissertation was prepared under the direction of the chairman

of the candidate's supervisory committee and has been approved by all

members of that committee. It was submitted to the Dean of the College

of Agriculture and to the Graduate Council, and was approved as partial

fulfillment of the requirements for the degree of Doctor of Philosophy.



March, 1968










Dean, College of Agriculture





Graduate School





Supervisory Committee:



Chairman





*7/ \ ^f>

c/.^AS/CC/ '^J^y' ___

























































































2,




Full Text

PAGE 1

TOXIC BAIT STUDIES WITH THE IMPORTED FIRE ANT, SOLENOPSIS SAEVISSIMA RICHTERI FOREL By CLIFFORD SWANSON LOFGREN A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1968

PAGE 2

L8l%-t Library n,nl^,^,''.^':r °<' FLORIDA 3 1262 08552 2711

PAGE 3

ACMOWLEDGEMENTS The writer wishes to express his deep appreciation to the members of his committee: Dr. F. S. Blanton^ Dr. C N. Smith, Dr. T. J. Walker, Mr. I. H. Gilbert and Dr. E. Lowe Pierce. He acknowledges the support of the Plant Pest Control Division, Agricultural Research Service, United States Department of Agriculture, under whose auspices the research was conducted. He especially thanks Mr. C. H. Gaddis for his suggestions during the course of the investi{;ations and Mr. C. E. Stringer, Jr., Mr. F. J. Bartlett and Mr. W. A. Banks for their assistance in various phases of the work. ii

PAGE 4

TABLE OF CONTENTS page ACKNOWLEDGEMENTS ii LIST OF TABLE vi LIST OF FIGURES viii ABSTRACT ix INTRODUCTION 1 LITERATURE REVIEW 2 Importation and Spread of the Imported Fire Ant 2 Life History 2 Biology and Ecology 3 Economic Importance 5 Medical Importance 5 Feeding Habits 6 Control 7 Residual insecticides 7 Baits 8 SCOPE OF STUDIES 10 METHODS AND MATERIALS 11 Laboratory Tests 11 Source and maintenance of ants 11 Food acceptability test 11 Toxic bait test 12 111

PAGE 5

METHODS AND MATERIALS (continued) _„„ Field Tests 2.8 Individual colony tests -|_g Control tests op Small plot design and counting procedures 22 Application procedures 25 Formulation procedures 25 Large scale aerial application procedures 26 RESULTS 27 Acceptability of 32 Commercially Available Fats and Oils 2? The Effect of Hydrogenation on the Acceptability of Cottonseed Oil 29 The Acceptability of Rancid Fats 30 The Effect of the Addition of some Anti-oxidants to Oncerefined Soybean Oil on Its Acceptance by Imported Fire Ants 3I A Comparison of the Toxicity of 7 Bait Toxicants with 3 Different Test Methods: Continuous, Limited and Transfer Feeding 32 Toxicity of h Toxicants in Peanut Oil When Transferred by Major or Minor Workers to Workers of the Opposite Size 34 The Acceptability of Baits to Individual Imported Fire Ant Colonies: An Evaluation of ik Different Carriers for Oil Baits 36 The Acceptability of Flour-Soybean Oil Bait Containing Various Concentrations of k Toxicants to Individual Imported Fire Ant Colonies kO Control of Imported Fire Ants with Granular Baits Containing the Toxicants Kepone or Mirex and Soybean Oil kl A Comparison of 6 Fats and Oils as Food Attractants in Toxic Baits for Imported Fire Ant Control kS The Effectiveness of k Toxicants in Flour-Soybean Oil Bait in Controlling Imported Fire Ants 47 iv

PAGE 6

RESULTS (continued) page The Effectiveness of k Toxicants in Corncob Grits-Soybean Oil Baits for Controlling Natural Infestations of Imported Fire Ants }^q The Effectiveness of Different Application Rates of Corncob Grits-Soybean Oil-Mirex Bait 5I The Effect of Mirex Concentration and Application Rate on Control of Imported Fire Ants with Granulated MirexSoybean Oil Bait 52 Control of Imported Fire Ants Following Aerial Application of Granular Mirex-Soybean Oil Bait to 96O Acres Near Orange Grove^ Mississippi 5lj. SUIMARY AND CONCLUSIONS 60 LITERATURE CITED 63 BIOGRAPHICAL SKES^CH 66

PAGE 7

LIST OF TABLES Table page 1. The acceptability of some commercially available fats and oils to imported fire ants . 28 2. The effect of hydrogenation on the acceptability of cottonseed oil as a food to imported fire ants. 29 3. Acceptability of soybean oil of different degrees of rancidity as food to imported fire ants. 3I k. The effect of the addition of 2 ant ioxidants to oncerefined soybean oil on its acceptance by imported fire ants. 32 5. The effective delayed toxicity range of 7 bait toxicants in peanut oil to imported fire ants as determined by 3 different test methods. 33 6. Imported fire ant bait transfer tests with various toxicants in peanut oil. 36 7. The acceptability to imported fire ants of baits consisting of various carriers impregnated with vegetable oils . 39 8. The acceptability to imported fire ants of floursoybean oil baits containing different concentrations of k toxicants. kl 9. Control of imported fire ants with various toxic bait formulations consisting of porous carriers impregnated with soybean oil containing the toxicants, Kepone or mirex. k2 10. A comparison of 5 fats or oils with soybean oil as food attractants in imported fire ant baits. kj 11. The effectiveness of k toxicants in flour-soybean oil bait for controlling natural infestations of imported fire ants. 2+8 VI

PAGE 8

LIST OF TABLES (continued) Table page 12. The effectiveness of ^4toxicants in soybean oilcorncob grits bait for controlling natural infestations of imported fire ants. 50 13. The effectiveness of a bait composed of corncob grits (85'/a) impregnated with soybean oil {lk-.92^'^) and mirex (0.075^) when applied at different rates per acre. 51 li;. The effect of mirex concentration and application rate on control of imported fire ants with granulated mirexsoybean oil bait. 53 15. Control of imported fire ants with granular mirex-soybean oil bait on subplots within a 960-acre test area near Orange Grove, Mississippi. 57 16. Control of imported fire ants following aerial application of granular mirex-soybean oil bait to a 960-acre test area near Orange Grove, Mississippi. 59 Vll

PAGE 9

LIST OF FIGURES Figure page 1. Materials used in toxic bait tests -carbon dioxide anesthetization chamber, vacuum tube, flower pot test chambers, bottles containing bait formxilations and bottle caps with cotton for offering toxic baits to ants. 16 2. A series of toxic bait test chambers sitting on wet peat moss. l5 3. Worker ants are placed in squares of grid pattern printed on standard mimeograph paper. 21 h. After ants are placed in squares as shown in Figure k, a portion of paper is folded over the ants and they are crushed with a photographic roller. 21 5. Dye that is forced out of the ants when they are crushed appears as colored spots on the paper. 21 6. An imported fire ant infested pasture typical of those used in small plot tests with toxic baits. 24 7. An aerial photograph of 960-acre test area near Orange Grove, Mississippi, showing locations of subplots and check plots used for evaluating effectiveness of granulated mirex bait. 55 Vlll

PAGE 10

Abstract of Dissertation Presented to the Graduate Council in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy TOXIC BAIT STUDIES WITH THE IMPORTED FIRE ANT, SOLEMOPSIS SAEVISSIMA RIGHT ERI FOREL By Clifford Swans on Lofgren March, I968 Chairman: Dr. F. S. Blanton Major Department: Entomology Studies were conducted to develop a toxic bait to control the imported fire ant, Solenopsis saevissima richteri Forel. The investigations were designed to find effective, inexpensive food attractants and delayed action toxicants that permit distribution of the bait in the colony before the worker ants are killed. A search was also made for granular carriers for the food attractants and toxicants that would carry the bait through vegetation to the ground where the ants forage. Vegetable oils with iodine values of about 100 and saturated animal fats such as lard and tallow were the most attractive food materials found. In addition, they are good solvents for the toxicants, relatively inexpensive and readily available. Highly unsaturated vegetable oils are unattractive. Rancidity and hydrogenation cause a decrease in the acceptance of vegetable oils. The most effective toxicant found was mirex. It gave delayed kill (less than I5/0 mortality after 2^^hours but at least SO'jo after 2 to 20 days) over a k)0-fold range of concentrations (0.0025-1.0-;^). In a bait ix

PAGE 11

transfer test in which large worker ants transferred bait to equal numbers of minor workers, it gave kill of the minor workers over a 10fold range of concentrations. It was the only toxicant that gave kill of major workers when baits were transferred to them by minor workers. Although not highly absorptive, the most useful and practical carrier was corncob grits. Mineral carriers such as attapulgite clay react with food oils, causing them to set-up or harden. The best bait formulation tested consisted of corncob grits (85;;^) impregnated with soybean oil containing mirex at concentrations of 0.075^ to 0.3^. It gave excellent control of ants in small plot tests. It is readily applied with various types of granular application equipment and is easily packaged and stored. Aerial application of this bait at the rate of 12 l/2 pounds per acre to a 960-acre plot gave over 99^0 control of ant colonies. The bait is now used routinely in the Imported Fire Ant Eradication Program.

PAGE 12

INTRODUCTION From the late 1950 's up to the present time, one of the most controversial insect pests in this country has been the imported fire ant, Solenopsis saevissima richteri Forel. The bulk of this controversy has swirled around the multi-million dollar program initiated in 1957 T^y the Federal government to eradicate this pest. Innumerable f^ articles have been written and speeches made regarding the justification or feasibility of this program and the hazards associated with the If (residual insecticides used in the early stages of the eradication campaign. The development of an effective toxic bait in the early 1960's alleviated much of the concern generated over the use of the residual insecticides and the associated potential dangers to wild life and man. Arguments continue, however, over the economic importance of the imported fire ant. The research reported in this dissertation is part of the extensive effort expended in developing the imported fire ant toxic bait mentioned previously.

PAGE 13

LITERATURE REVIEW Importation and Spread of the Imported Fire Ant The imported fire ant is native to South America, occurring principally in northern Argentina and Uruguay (Wilson, 1953)' Other subspecies and related species occur throughout much of that continent. It was first reported in the United States by H. P. Loding in 1929 in U.S.D.A. Insect Survey Bulletin 9Creighton (1930) noticed this ant in Mobile in 1926 and stated that Mr. Loding had said they occurred on the Mobile Bayfront in I918. Since its introduction, which presumably occurred with ballast unloaded from boats from South America, the species has spread over an area encompassing about 100,000,000 acres in the states of Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina and Texas. Much of the early spread was undoubtedly attributable to movement of intact colonies or fertile queens with nursery stock from the Mobile area (Anonymous, I958). Federal and state quarantine restrictions have essentially eliminated spread from this and most other man related sources since their institution in 1957Natural spread during mating flights has probably accounted for most of the spread since then. Life History ( The life history of the imported fire ant is similar to that of many other ant species (Anonymous, 1958)A colony starts with a fertile queen

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after the nuptial flight. She removes her vings after alighting on the ground and inmediately begins excavating a brood chamber in the soil or under some protective object. She starts to lay eggs within a few daySj and these hatch in 8 to 10 days. The young larvae are fed by the queen from food reserves within her body. The larval stage normallT^ lasts from 6 to 12 days, and the pupal stage from 9 to l6 days.^ The first adults are knoA>ni as minim workers because of their small size, which is the result of the limited food available to them. The minim workers begin foraging and take over the care of the brood. The imported fire ant is a polymorphic species, and workers of various sizes can be found in the colony after a few months. The time required for the colony to produce alate forms varies, depending upon climatic conditions. Khan {l9<'-<'^) has reported that in laboratory and field tests at Starkville, Mississippi, about 270 days are required. Rlioades (19 7)? however, stated that his field observations in northern Florida indicated a colony could produce alates in 15 to 18 weeks. From these observations, the life cycle of an imported fire ant colony, that is, the time from the start of a colony by a fertile queen to the production of virgin alates capable of mating flights, is h 1/2 to 9 months, depending upon prevailing climatic and ecological conditions. Biology and Ecology The imported fire ant is extremely adaptable, and once a colony is established it can survive under a variety of ecological situations. In South America, it occurs from sea level to altitudes in the Andes above 10,000 feet (Hays, 1958). In the United States, however, cold weather has apparently slowed the northward spread of the species, and it has not

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established itself north of Texas, southern Arkansas, Mississippi, Alabama and North Carolina. Preferred locations for queens to establish nev colonies are well-drained, closely grazed pastures, ditch banks and dikes, road shoulders and cropland (provided it is not cultivated after the queens have established their brood chambers ) . Swamps and woods are generally less favorable, but in areas subjected to imported fire ant mating flights for many years, colonies can become established even in these areas. One of the most characteristic habits of the species is its tendency to build nests which consist of mounds of dirt, honeycombed with small tunnels or galleries (Anonymous, 1958)These mounds vary in size, depending upon the age of the colony and the soil type. In clay soil, some movmds may be 2 to 3 feet in height and 3 to 4 feet in diameter at the base. The area under the mound is also honeycombed with txinnels, some of which may reach a depth of 5 feet. The mound is the main center of activity for the colony. The queen, the brood, alate males and queens and a large portion of the workers are found in it. Characteristically, the moixnd is covered with a hard crust of dirt. The ants leave the nest through tunnels which extend for long distances just beneath the soil surface. Any disturbance of the mound results in an outrush of large numbers of workers which attempt to sting the disturbing object or animal. Afterwards, the ants quickly carry off the exposed brood into the undisturbed tunnels and usually repair the mound. Occasionally, the ants will move the nest; the reasons for this are not known, but it presumably is due to some undesirable disturbance, ecological or physical factor or a response to some new food source.

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Economic Importance Since the advent of the Federally sponsored eradication program, there has been an extensive debate about the economic importance of the imported fire ant. E^rly reports (Wilson and E^ds, 19^9; Anonymous, 1958) indicated that the ants caused considerable damage to various crops (corn, okra, cabbage, potatoes, nursery stock, etc.)Damage in the Alabama coxmties of Baldwin and Mobile during 19l<-9 was estimated to exceed $500,000.00.) More recent reports such as that of the Fire Ant Committee of the Georgia Academy of Science (Bellinger et al., 196'+) have challenged the importance of the imported fire ant as an economic pest. The theory has been advanced that the habits of the imported fire ant have changed so that it no longer feeds extensively on crops. This conclusion ignores completely the fact that early observations were made prior to the time when chlorinated hydrocarbon insecticides became an integral part of farming operations for control of a wide variety of pests. Many of these insecticides are extremely toxic to imported fire ants. Incidental observations by the author have shown that ^imported fire ants do feed very readily on okra flowers and the roots of cabbage and corn seedlings in fields where no insecticides have been applied^ There is little question that the imported fire ant is a nuisance pest primarily because of its mound building activities and aggressive stinging habits. The economic importance of this depends on the reaction of the people involved. Obviously, if the nuisance is sufficient to cause a person to expend money to kill the ants, they are an economic pesti Medical Importance The imported fire ant is of medical importance because of its

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stinging habit. A sting of the imported fire ant is very painful and is accompanied by a strong itching sensation. The venom injected is a strong necrotizing agent which destroys the cells in a small area around the point of penetration. This results in the development of a sterile pustule after about 2^4hours. Because of extreme sensitivity to the venom or an excessive number of stings, individuals may undergo anaphylactic shock which can result in death (Adrouny et al,, 1959; Caro et al., 1957; Jung and Derbes, 1957)Of lesser importance but still of considerable concern are secondary infections which can result if the pustule is broken from scratching the affected area. Feeding Habits The imported fire ant is an omnivorous feeder. The list of live plants and animals and products processed from them which are subject to attack is extensive. The ants ingest all 3 major food categories; carbohydrates, proteins and fats. Hays and Arant (196O) and Bartlett and Lofgren (196I) gave long lists of foods which were accepted in laboratory * tests but concluded that vegetable and animal fats and oils were the most preferred foods. In the field, worker ants have been observed attacking and carrying back to the colony a wide variety of small arthropods. Larger animals also may be attacked and killed. However, the author's observations have indicated that this usually does not occur unless the animals are in a weakened condition. Newborn animals are very often subject to attack, and the ants feed on carcasses of large animals that have died from other causes. Feeding on plants occurs and seems to be most pronounced on seeds or germinating seeds and seedlings (Wilson and Bads, 19^^-9 )• Young or mature plants are not fed on to any

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7 extent. One exception appears to be the flowers of okra plants. The ants apparently feed on nectar or oils produced in the flowers. Feeding on honeydew of aphids and mealybugs has been reported (Anonymous, 1958; Green, 1967)' The ants in some instances build "chimneys" or tunnels along the stems of the plants and around the aphids. Although imported fire ants are voracious feeders, the colony can withstand extended periods of drought or flooding when foraging is extremely difficult or impossible. "T*^" '' Control ' \J> Residual Insecticides Ci > Insecticidal control of the imported fire ant until j^eeentiy has relied primarily on the chlorinated cyclodiene insecticides such as chlordane, heptachlor, dieldrin and aldrin., Laboratory tests showing the toxicity of these and over 3OO other compoixnds have been reported by Lofgren et al. (196^) . Early control efforts were directed toward killing the ants in their individual moxinds (Green, 1952; Coarsey, 1952). This method never proved highly effective. Numerous worker ants were killed, but ifthe queen was not killed, the survivors moved their colonies to a new location. Broadcast treatments in which all the surface area was treated were much more effective (Eden and Arant, 19^9; Blake et al., 1959)' Dust, emulsion concentrate, granular and fertilizer-insecticide formxilations were tested. Dosages of 1 to 4 pounds per acre gave residual control for 1 to 1+ years depending upon the insecticide used. When the Imported Fire Ant Eradication Program was initiated in 1957^ the standard treatments adopted were 2 pounds per acre of heptachlor or dieldrin as granular formulations. This procedure was later

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8 changed to 2 applications of l/4 pound per acre of granular heptachlor applied at intervals of 3 to 6 months (Lofgren et al.^ 19^1; Lofgren et al., 1965). This was done to save on application costs and to reduce undesirable residues and hazards to wild life. ^Residual treatments are not used in this program at the present time. However, for small areas where residues are not a problem, these insecticides still provide the best and longest control.^ Baits Poison baits have been a favored approach to ant control for many years. The first large scale use of baits was in conjunction with control of the Argentine ant, Iridomyrmex humilis Mayr in the early 1900's. Barber (1916) developed a sweet bait containing tartaric acid as the toxicant. Other baits for this species with sodixom arsenite or thallium sulfate as toxicants have been reported by Mallis (195^)' Effectiveness of the baits reportedly was dependent upon the worker ants feeding it to the queen. The slow action of the toxicants permitted this to be done without killing the worker ants prematurely. Travis (1939) reported on studies with the native fire ant, Solenopsis geminata (F. ), in which he tested syrup baits containing thallium sulfate and thallium acetate. Neither fonnulation was consistently effective in the field. Green (1952) tested a bait consisting of thallium sulfate with corn meal and oil against the imported fire ant. It worked effectively on captive colonies but was ineffective when scattered around mounds in the field. (Studies conducted by Hays and Arant (1960) indicated that peanut butter and Kepone (decachlorooctahydro-1,3-^metheno-2H-cyclobuta [cd] pentalen-2-one) at a concentration of 0.125^ and packed in soda straws gave control of imported fire ants )

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At the same time, Bartlett and Lofgren (196I) tested a bait consisting of peanut meal-peanut oil and Kepone (0.25'/o) which gave 951 control of imported fire ants on small field plots after I6 weeks. They also reported on a useful technique for determining the acceptability of baits based on the incorporation of dye in the food. After the dyed baits were exposed to ant colonies for 2k to k8 hours, 100 worker ants from each colony were examined for the presence of dye. Tests with several vegetable and animal oils showed that corn, cottonseed, peanut, olive, fish, cod-liver and neat's-foot oils were very attractive {k^';b to 71/j of workers contained dye after 2k hours). Tung oil was completely unacceptable.

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SCOPE OF THESE STUDIES The studies discussed in this report were initiated to develop an effective and safe "bait which could "be used in a large scale eradication or control program. ( The 2 primary ingredients of an ant bait are (l) a highly attractive food material that is cheap and readily available and (2) a highly effective toxicant with a delayed toxic action so that it may be distributed throughout the ant colony, and especially to the queen, before the workers are killed. To be entirely practical, the bait must be formulated in such a way that it can be distributed over large acreages and be readily found by the ants, ('since the ants forage primarily on the soil surface, a granular bait which passes through vegetation is most desirable. Based on these requirements, experimental procedixres were developed or modified for the evaluation of foods, toxicants and granular carriers in the laboratory and field, and numerous series of tests were conducted with them. 10

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METHODS AND MATERIALS Laboratory Tests Source and Maintenance of Ants Attempts to rear colonies from newly mated queens or to maintain captive field colonies in the laboratory for long periods of time (over 2-3 months) were unsuccessful. For the food acceptability tests J ant colonies were collected as needed, placed in large wash tubs with soil and moved into a greenhouse. The ants were kept from escaping either by placing the tubs in large shallow pans filled with water or by dusting the inner sides of the tubs with talc. The colonies were fed for a week or more before they were used in any tests. Food consisted of insects, vegetable oils, dog food and W/o sucrose solution in water. This feeding period was necessary to decrease the activity of the ants and make them more selective in food preference. Colonies which continued to feed very avidly or very sparingly were discarded. Ants for the bait toxicant tests were collected the same day the tests were initiated and were not prefed. All ants were obtained from field colonies located in or near Gulfport, Mississippi. Food Acceptability Tests The search for the most suitable food material was limited to fats and oils. This was done primarily because prior research had indicated this type of food was very acceptable, readily available and generally 11

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12 not very expensive. In addition, fats and oils are easy to formulate on granular carriers, they are good solvents for most insecticides and their water repellency makes bait form\ilations containing them less apt to be destroyed by rain or dew after application. The test methods employed were the same as those described by Lofgren et al. (196I). Essentially, they consisted of comparing the feeding activity of the ants on each food with that on a standard material (peanut oil). The fats and oils were applied to 1-inch-square pieces of blotting paper and placed on pieces of alumintim foil on soil in a tub containing an imported fire ant colony. After 5 minutes, the ants feeding on the candidate material and the standard were counted. The ants were then removed from the food, the position of the 2 foods on the mound were reversed, and a second 5-minute test was conducted. One or more tests with 8 replications each were made with each food material. An acceptance ratio for each material was determined by dividing the total number of ants feeding on the candidate material by the total number feeding on the standard. Using this procedure, h series of tests were conducted to determine (1) the acceptability of 32 commercially available fats and oils, (2) the effect of hydrogenation on the acceptability of cottonseed oil, (3) the acceptability of rancid oils and {h) the effect of anti-oxidants on acceptability of fats and oils. Toxic Bait Test The need of a laboratory method for rapidly screening a large number of bait toxicants against imported fire ants became very evident in early work with baits. Many test methods for evaluating bait toxicants on other insects have been reported; however, these methods are primarily

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13 designed to select insecticides which give a quick kill. The objective of a test for selecting toxicants for use in "baits against a colonial insect, such as the imported fire ant, must he to detect insecticides which are characterized "by a delayed killing action. The reason is that the foraging ants must not "become alarmed by the presence of the toxicant or be killed before the bait is brought back to the colony. Observations in the field have shown that once the ants become aware that they have taken a poisoned bait, they will usually cease feeding on it and move the colony. The following procedures were employed in the laboratory studies. Small plastic flower pots, k2 mm in diameter at the base and 63 mm at the top with an upright rim l6mm high were used as test chambers. The rim formed a narrow ridge at its base inside the pot. There were 3 small holes in the bottom. A layer about l/i»-inch thick of plaster of paris mixed with cement (9:1 ratio) was poured over the bottom of the pot and allowed to harden. When the pots were placed on wet peat moss, the plaster of paris acted as a wick to draw up water and maintain a high humidity, which was essential for the survival of the ants. The cement was added to make a harder mixture which the ants could not tunnel through for escape. The ants were confined in the containers by small plate-glass discs with a diameter slightly less than that of the rim, so that they rested on the ridge between the rim and the tapered portion of the chamber. The insides of the pots were dusted lightly with talc. The talc had to be used sparingly because ants are easily killed by it, especially in the absence of moisture or if they are in a weakened condition. In preparing the toxic bait, the candidate insecticides were

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Ik dissolved directly in the food material; i.e., either peanut oil or 10'^ sucrose solution, depending upon the solubility of the chemical. The hait was offered to the ants on cotton plugs in small vial lids. Worker ants were collected with the aid of carbon dioxide and an aspirator and placed in the test containers the afternoon of the day preceding the test. This time interval permitted the ants to recover from the effects of the carbon dioxide and to orientate themselves to the container before the start of the test. Ants that died during this 2U-hour period were replaced with others similarly conditioned. Figures 1 2 illustrate various aspects of these procedures. As mentioned previously, the objective of the tests was to determine whether a toxicant would give delayed toxicity. In these tests, delayed toxicity was defined as less than 1% mortality after a 2i+-hour exposure and more than 89^0 mortality at the end of the test period (2 to 20 days). Three different test methods -continuous feeding, limited feeding and bait transfer -were used. In the continuous feeding procedure, ad libitum feeding by the ants was permitted throughout the test period. Observations for dead ants were made over a 20-day period. It was recognized that this test did not differentiate between delayed toxicity, temporary repellency, fumigant action, or accumulative toxicity during the prolonged feeding period. In the limited feeding tests, the previously described procedure was modified so that the ants were allowed access to the bait for the initial 2k hours of the test period, after which the toxic bait was removed, and the ants were starved for 2k hours. The ants were then provided with uncontaminated peanut oil as food for the remainder of the 20-day test period. The limited exposure to the toxicant insured that any delayed

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Figure 1. --Materials used in toxic bait tests -carbon dioxide anesthetization chamber^ vacuum tube^ flower pot test chambers) bottles containing bait formulations and bottle caps with cotton for offering toxic baits to ants. Figure 2.--A series of toxic bait test chambers sitting on wet peat moss.

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16

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17 toxicity exhibited was due to delayed action rather than acciimulative action. Imported fire ants readily pass food from one individual to another. The "bait transfer technique was designed to determine how effectively toxic baits are passed between the worker ants. Worker ants were separated into 2 groups according to size. Major or minor worker ants were fed bait for 2^ hours and then transferred to a clean test chamber containing unfed ants of the opposite size. This sizing procedure permitted a determination of which ants had been pre-fed. Two experiments were conducted with these methods to thoroughly evaluate 7 promising toxicants. In the first experiment, the delayed toxicity range for the 7 toxicants was determined by the continuous and limited feeding tests, and the effective toxicity range was determined in the bait transfer test. T^-ro tests V7ith 2 replications each were conducted. Twenty worker ants were used in each replication in the continuous and limited feeding tests. In the bait transfer test, 10 major workers transferred bait to 10 minor workers in each replication. The major workers were kept with the minor workers throughout the test, but mortality counts were made only on the minor workers. Observations for mortality were made over a 20-day period. The concentrations of each toxicant in the peanut oil are recorded in Table 1. In the second experiment, h toxicants were evaluated with the bait transfer test to (l) compare their toxicity when 20 ants were pre-fed and allowed to feed 10 unfed ants and (2) determine differences in toxicity to major workers and minor workers. The toxicant concentrations were the same as in the previous test. The pre-fed ants were separated from the unfed ants after 3 days. Observations for mortality were made over a 31-
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18 The toxicants evaluated in these studies were: Bayer 3^911 Phosphonothioic acid, methyl-, 0,2,4-dichlorophenyl O-methyl ester Bayer 3892O Coumaphos 1-Fluorochlordene Hooker HRS12i^3 Kepone Mirex 6,9-Methano-3H-2,U-'benzodioxepin, 6,7,8,9,10,10-hexachloro-l,5,5a, 6, 9 J 9a-hexahydro3-niethyl, chlorinated to contain 70'^ total chlorine Phosphorothioic acid, 0,0-diethyl ester, 0-ester with 3-chloro-7hydroxy-^-methylcoumarin U,7-Methanoindene, U,5,6,7,8,8-hexachloro-l-fluoro-3a,^,7,7a-tetrahydro1,2-Propanediol, 3-[ (l,la,3,3a,U,5, 5,5a, 5'b,6-deGachlorooctahydro-2-hydrox;;,'-i, 3,^-nietheno-2H-cyclobuta[cd]pentalen2-yl)oxy]~ ~ l,3j^-Metheno-2H-cyclobuta[cd]pentalen2one, decachlorooctahydrol,3j)^-Metheno-2H-cyclobuta[cd]pentalene, dodecachlorooctahydroField Tests Individual Colony Tests The acceptability of toxic and non-toxic baits was determined with individual imported fire ant colonies as an intermediate step between laboratory studies and attempts to control ants on small plots. The most useful procedure for this purpose was that described by Bartlett and Lofgren (I96I). With this test, oil baits were treated with Calcooil red or blue dye (0.25'^ by weight). One hundred grams of bait ^vas scattered around the base of each mound. After 2k hours, worker ants were collected and examined for the presence of dye in the gut. This was done by placing 100 randomly selected ants (killed with methylene chloride)

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19 on a sheet of white paper on part of which a grid pattern of 100 l/i^-inch squares was printed. (Figure 3) After the ants had "been placed individually within the squares, the paper was folded in half over the ants. A photographic roller was rolled over the folded paper, crushing the ants and forcing their gut contents onto the paper. If dye was present, it appeared as a stain on the paper. (Figures k and 5.) The number of stained squares was determined "by viewing the paper over a light box. All of the tests were run with ant colonies along roadsides where they were readily accessible and adequate space between colonies was easily attained. Six replicates were made with each bait. This test was particularly useful because it gave a rapid indication of the acceptability of a bait (as indicated by its actual ingestion) with a minimum of effort. Although it was not done in these tests, the procedure could be expanded so that the distribution of the bait to all ant forms in the colony could be determined. A more accurate evaluation could undoubtedly be attained with the use of a radioactive material such as P-^ . This would, however, be at the sacrifice of speed and efficiency because of the need for much greater care in handling the bait and the treated ants. Two series of experiments were conducted using these procedures. In the first series, baits consisting of vegetable or animal oils and fats in various carriers were evaluated. In the second, the repellency of various concentrations of k of the most promising toxicants combined with a soybean oil (UO'/o)-white flour (GOio) bait was determined. This bait was used in combination with the toxicants because it is readily and consistently accepted by ant colonies in the field.

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Figure 3' --Worker ants are placed in squares of grid pattern printed on standard mimeograph paper. Figure k. — After ants are placed in squares as shown in Figure k, a portion of paper is folded over the antSj and they are crushed with a photographic roller. Figure 5. — Dye that is forced out of the ants when they are crushed appears as colored spots on the paper.

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21

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22 Control tests Small plot design and counting procedures . — Considerable difficulty vas encountered in obtaining a good evaluation of a bait in preliminary field tests when 1-acre plots were used because of cross feeding by the ants from one treated plot into another or because of early reinfestation by colonies from adjacent untreated land or from plots where poor control was obtained. To minimize these problems, the tests were conducted on plots of 6 to 8 acres each. Three 1-acre subplots were set up within the large plots. The subplots were at least 50 feet from each other and from the border of the large plot. Only one large plot was treated with each formulation. All of the plots were located in pastures. Figure 6 shows an imported fire ant infested pasture typical of those used in the tests. The control obtained with each bait was determined by the percent reduction in active imported fire ant mounds on the subplots at intervals after treatment. An ant mound was considered active as long as more than 20 worker ants could be found, or if a wingless queen was found with less than 20 workers. This was done to eliminate from the counts mounds containing small numbers of worker ants, which are often found in old mounds that have been abandoned. Mounds in which only alate males or females remained were considered inactive. De-alated queens found alone were assumed to be from post-treatment mating flights. At the l6or 26-week counts, incipient colonies were occasionally found which indicated reinfestation from mating flights. Since these colonies were not present at the time of treatment, they were excluded from the total number of active colonies on the plot. This was done so that the results of the tests would reflect only the effect of the baits on the ant population present at the time of treatment. Only those

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Figure 6. An imported fire ant infested pasture typical of those used in small plot tests with toxic baits.

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2i^

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25 colonies with very small mounds and a predominance of minor workers were excluded. Application procedures . — Cyclone hand seeders or powertakeoff Cyclone seeders mounted on jeeps were employed for distributing granular baits in the early tests. In later tests ^ in which the corncob grits carrier was used exclusively, the baits were distributed with a jeepmounted Buffalo turbine blower. The standard slurry (flour and soybean oil) bait was applied with a specially designed applicator which pumped the bait out each end of a 10-foot boom and dropped it directly to the ground in strips 10 feet apart. With the exception of the bran baits, the granular formulations were distributed uniformly over the entire plot (30-foot swath with Buffalo turbine and 20-foot swath with the Cyclone seeder). The bran baits were applied in ij-foot strips at 20-' foot intervals across the plot. Slurry baits were applied at the rate of 6 pounds per acre; rates for the granular formulations varied and are indicated in the table of results for the various tests. Formulation procedures .-The bait formulations were prepared by pouring the oils over the granules or flour as they were mixed in a large commercial electric food mixer. Because of the viscosity of the oils, they do not readily penetrate porous carriers. This was overcome by heating the oils to 100 c 150°C before application to the carriers. With this procedure, it was in most instances possible, within the carrier's absorptive limits, to obtain dry flowable formulations. In the tests in which carriers were evaluated, the concentration of toxicant in the formulations was based on the weight of the oil in the bait rather than total formulation weight. In the tests in which different carriers were compared and in some

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26 of the bait toxicant evaluations, the standard "bait consisted of kO'-^ soybean oil and 60/0 vhite flour. Kepone at a concentration of 0.25'^ in the oil was added to this bait . Large scale aerial application procedures . — A 960-acre block of land near Orange Grove, Mississippi, was selected for an aerial application test with granulated mirex bait. It included varying types of land cover and terrain. Approximately 50^ of the area was in woodland, idle or waste land. The remaining area consisted of small pastures, cultivated fields, gardens and pecan and timg groves. Thirtythree small plots were set up within the area for making the preand post-treatment counts for ant colonies. The size of these plots ranged from about l/2 to 1 1/2 acres with the majority slightly under 1 acre. The pre-treatment count of fire ant colonies per plot ranged from 7 to k^. The bait formulation consisted of O.O75/0 mirex, ll+.925/j crude soybean oil and 85'?^ 10-40 mesh corncob grits and was prepared by a commercial formiilator. It was applied at the rate of 12 l/2 pounds per acre {k.2 gms of mirex per acre) with a Piper Pawnee airplane equipped with a Texas A & M type granular distributor. The overall swath width obtained with the distributor was 60 feet; however, the actual swath width flown with the plane was 30 feet. This was done to insxire an adequate overlap of the swaths, and it also permitted the operation of the plane under higher wind conditions than would have been possible with a narrower overlap of swaths. The swaths were marked by a man stationed at each end of the plot holding specially designed balloons covered with nylon covers and filled with helium. These are manufactured commercially under the name, Kytoon.

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RESULTS Th e AcGepta"bllity of 32 Commercially Available Fats and Oils Thirty-two commercially available fats and oils were compared for their attractiveness as foods to the imported fire ant. In addition, 2 different grades or samples of 5 of the materials (hog grease, lard, linseed oil, soybean oil and beef tallow) were tested. Nineteen of the fats or oils gave acceptance ratios as good as or better than the peanut oil standard (>0.90). (See Table 1.) The most attractive fats were the 2 types of tallow and 1 of the 2 lard samples. It is evident that the acceptance ratio for any fat can vary considerably from sample to sample as evidenced by the results with lard (0-97 and 1.75) and soybean oil (16 samples of crude soybean oil ranged from 0.59 to 1.01; 38 samples of once-refined soybean oil varied from O.97 to 2.01). Variation in the peanut oil standard was avoided by running all tests with oil from the same sample. The sample was stored in a refrigerator to avoid rancidity. The results with soybean oil also showed that a crude grade of fat is not as acceptable as the refined. The least attractive oils were those classified as drying oils which are highly unsaturated. Examples of this type of oil are the following which had acceptance ratios ranging from 0.05 to 0.53: linseed oil (l.V. 170-20if), oiticica oil (l-V139-155), perilla oil (l.V. 193-208) and tung oil (l.V. l60-175)The iodine value (l.V. ) is a measure of the degree of linsaturation. Common edible oils such as peanut and soybean oils have I.V.'s of about 100. 27

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28 Table l.--The acceptability of some commercially available fats and oils to imported fire ants. Acceptance Fat or oil^ No. of tests ratio Vegetable Almond J sweet k Apricot kernel h Avocado 2 Castor 5 Chaulmoogra 2 Coconut 3 Corn 2 Cottonseed 2 Linseedj raw Ij. Linseed, sion thickened 2 Oiticica 1 Olive 2 Palm 1 Palm kernel 2 Peanut Perilla 1 Poppy seed 2 Rapeseed 5 Ricebran, crude k Safflower 3 Sesame 3 Soybean, crude^ 49 Soybean, once refined*^ 111 Tung 8 Wheat germ 4 Animal Butter i). Butter oil 1 Cod liver 2 Dogfish liver 1 Grease oil, hog'^ 2 Grease, hog, white^ 7 Grease, hog, yellow® 8 Lard, Sample A^ 4 Lard, Sample B^ 2 Neat ' s-f oot 12 Tallow, beef, fancy ' 6 Tallow, beef, top white 3 1

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29 The Effect of Hydrogenation on the Acceptability of Cottonseed Oil A solidified fat would "be preferable in a bait to eliminate loss of the fat to other absorptive surfaces and to deter leaching of the fat during exposure to rains . One means to accomplish this is to hydrogenate the fatj thus decreasing its degree of unsatirration. A study was therefore made to determine the effect of hydrogenation on the acceptability of cottonseed oil. The samples of hydrogenated cottonseed oil were prepared by Dr. T. H. Hopper, Chief , Industrial Crops Laboratory, Southern Utilization Laboratory, Agricultural Research Service, United States Department of Agricultvire, New Orleans, Louisiana. Nine samples with varying iodine values were prepared. The results (see Table 2) show that as the degree of hydrogenation increases (l.V. 88.1 to I.V. 27'7) the acceptance ratio decreases (O.76 to 0.1^). Table 2. --The effect of hydrogenation on the acceptability of cottonseed oil as a food to imported fire ants.^ Degree of hydrogenation as indicated by iodine number Acceptance ratio 88.1 0.76 79.9 -75 72.7 -56 63.9 -^2 53-7 -32 U7.7 •2it39.7 .22 33.8 .12 27.7 -1^ a Average results from 2 tests with 8 replications each.

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30 The Acceptability of Rancid Fats With reference to man, rancidity refers to any objectionable odor or taste which develops in fats over a period of time. The principal chemical changes which occur are a result of hydrolysis or oxidation. They can be brought about by heat, light, moistiire, air, enzymes, bacteria and metals. During the chemical changes, free fatty acids, ketones, peroxides and other substances are formed. The method used for assessing the degree of rancidity in these tests involved the determination of a peroxide value. This value refers to the oxygen content in milliequivalents per kg of fat sample and is a direct representation of the amount of oxidized fat. A sample of rancid soybean oil with a peroxide value of 600 was compared with nonrancid soybean oil with a peroxide value of 2 for acceptability to Imported fire ants. The average acceptance ratio for the rancid oil was O.37 (5 tests) compared with 0.8? for the nonrancid oil (6 tests). In a second experiment, the acceptability of k rancid oil samples that had been extracted with pentane from soybean oilcorncob grits baits was determined. These baits had been exposed to normal weather conditions outdoors until the oil reached various stages of rancidity. It is evident from the results (Table 3) that rancid oil is much less attractive to Imported fire ants. The acceptance values for rancid oils were inversely proportional to the peroxide values for every sample of oil tested.

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31 Talsle 3. --Acceptability of soybean oil of different degrees of rancidity as food to imported fire ants.^ Rancidity of oil as indicated by peroxide value Acceptance ratio 33 1-^2 191 oAi 215 .16 22i).13 a Average of 2 tests with 8 replications each. The Effect of the Addition of some Antioxidants to Once-refined Soybean Oil on Its Acceptance by Imported Fire Ants Anti-oxidants are chemicals which delay the development of rancidity in fats. As a result, a test was conducted to determine the effect of the addition of various concentrations of 2 anti-oxidants to refined soybean oil on its acceptance by imported fire ants. The 2 antioxidants, which were obtained from the Eastman Chemical Company, were Tenox 7 (butylated hydroxyanisole 28fo, propyl gallate 12^0, citric acid ^lo, glyceryl monooleate 20/o, propylene glycol 3h''fo) , and Tenox S-1 (propyl gallate 20/o, citric acid lO'fo, propylene glycol TOfo). They were tested at the concentration of O.O5, 0.1, 0.25 and 0.5/0 in the oil. Sixteen replications were made with each. The results are presented in Table k. None of the concentrations of the anti-oxidants appreciably affected the acceptability of the soybean oil in these tests although the acceptance ratios were still a little below that of the standard (1.39). At the highest anti-oxidant concentration, 0.5/3, the acceptance ratios were O.92 and O.93. The results suggest that either of these materials could be used in oil baits to preserve them during storage;

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32 however, tests were not conducted with aged baits to determine if they actually would retard rancidity without loss of attractiveness. Table U.--The effect of the addition of 2 anti-oxidants to once-refined s oyb ean oil on its acceptance by imported fire ants. Antioxidants Cone. Avg. no. of ants Acceptance (;4) feeding on standard ratio Tenox 7 0-05 62 0.1 63 0.25 60 0.5 77 Tenox S-1 0.05 ^^ 0.1 60 0.25 58 0.5 ^7 ( Check )^ 80 1.

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33 in the continuous feeding test over a 50to 100-fold dosage range and in the limited feeding test over a 10to 25-fold range. Neither conpound gave any appreciable delayed kill in the "bait transfer test. The remaining compounds gave delayed kill only in the continuous and limited feeding tests and over a range vhich varied from 2to 10-fold. In order of effectiveness they were: Bayer 38920, coumaphos, Bayer 309II and 1f luorochlordene . Table 5' — The effective delayed toxicity^ range of 7 bait toxicants in peanut oil to imported fire ant workers as determined by 3 different test methods. (Corrected for check mortality by Abbott ' s formula . )

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3k Table 5 •--Continued Lethal time (days) required to kill 1570 and 90;;-i of ants with each of the following test methods: Cone. Continuous feeding Limited feeding Transfer feeding^ (^0 LT-1$ LT-90 LT-1$ LT-90 LT-15 LT-90 Toxicant Bayer 38920 Coumaphos .001 .0025 .005 .01 .025 .05 .1 .001 .0025 .005 .01 .025 .05 .1 1-Fluorochlordene Bayer 309II Check .001 .0025 .005 .01 .025 .0025 .005 .01 .025 .05 .1 8 5 k h 2 2 1 15 7 5 3 1 3 2 2 1 6 5 3 1 17 >20

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35 the ratio of prefed to unfed workers vas 2 to 1. The observations in this experiment (see Table 6) were made over a 31-^y period compared to 20 days in the previous test. The results can be compared, however, if the LTgo values of less than 21 days are considered. On this basis all the toxicants with the exception of Bayer 30911 gave kill of the minor workers over a greater range of dosajjes when the ratio of prefed major workers to unfed minor workers was 2 to 1 than when it was 1 to 1 (see Table 5)The range was 100-fold for mirex, lU5-fold for HRS-12i4-3, 4fold for Kepone and 2-fold for Bayer 309II. The increased toxicity was greater than would be theoretically expected. Presumably, twice as much bait and toxicant was available to the minor workers and, therefore, the lowest dosage causing mortality might drop by one-half. Actually, it dropped by a factor of k to 10. Since field colonies were used in these tests, the increased toxicity must be due to differences such as the degree of hunger of the ants, body weight, or factors other than nifflibers which would affect the quantity of bait actually transferred. In the test where minor workers transferred bait to major workers, only mirex was toxic enough to give kill over a range of dosages (0.1l.Ofo). This undoubtedly reflects a smaller uptake of bait by the minor workers and a need for more toxicant to kill the major workers.

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36 Table 6. --Imported fire ant "bait transfer tests with various toxicants in peanut oil.^

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37 vegetable oils to Imported fire ant colonies in the field. The various "baits evaluated^ the composition of each and the results are recorded in Table ?. Acceptance of the standard white flour-soybean oil bait varied from ^O'^ to 75'^This variation probably reflects such differences as temperature and availability of natural foods. Puffed barley grits, aged pine sawdust, kenaf or okra hurds and corncob pith formulations all gave results comparable to or better than the standard in their respective tests. Wheat bran and corncob grits formulations were slightly less attractive; however, it is believed this was a result of a reduced amount of oil in these formulations. The fresh pine sawdust formiilation was definitely less attractive. The results with vermiculite were erractic, and even at the highest oil concentration (75fo), the feeding rate was reduced 25^ in comparison to tne standard. Feeding on the clay granular formulations varied from lO/o to 47/j as compared to 75/3 for the standard. All work with these carriers was discontinued when it was found that the oils reacted with the granules and set up or hardened within a few days to several weeks after formulation. It was concluded from the tests and information on availability of the carriers that puffed barley grits, wheat bran, aged pine sawdust and corncob grits were the only carriers worthy of extensive field tests for controlling imported fire ants.

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Tatle 7— Footnotes One hundred grams of bait scattered around each mound; six replications unless otherwise indicated. The mesh size range of the granular carriers was as follows: puffed barley grits, 6-16; corncob grits, 10-40; sawdust, minus 8; okra hurds, kenaf hurds and corncob pith, 830; vermiculite and various clay granules, 20-ij-O. The granulated stalk of this plant; kenaf is also called ambary. Hibiscus cannabinus L. c The granulated stalk of this plant.

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39 Table 7.--The acceptability to imported fire ants of baits consisting of various carriers impregnated with vegetable oils.^

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1^0 The Acceptability of Flour-Soybean Oil Bait Containing Various Concentrations of k Toxicants to Individual Imported Fire Ant Colonies In early field studies it vas found that most insecticides exhibit some degree of repellency when combined with a bait. As a result, tests were conducted with k promising toxicants (mirex, Kepone, HRS-1243 and Bayer 30911) "to determine their effect on the acceptability of floursoybean oil baits. Various concentrations of the toxicants which bracketed the upper levels of their toxicity range were tested. Feeding activity was compared with that on the same bait without toxicant. All the toxicants showed some repellency as the insecticide concentration was increased (see Table 8). Mirex was definitely the least repellent. The average number of ants containing dye at the 3 lowest concentrations (0.05, 0.1 and 0.25^i) was 8k-fo. The acceptance decreased to Gkfo at a concentration of ifo. The decrease in acceptance was very pronounced with the other 3 compounds; the ranges in acceptance from the lowest concentration to the highest were as follows: Kepone (80^ to 2^p) , HRS-1243 (83/c to 28/0) and Bayer 309II (Tl/a to 0^^). Some of the apparent repellency in these tests could be due to toxic action of the insecticide; however, the insecticides were chosen because of their delayed action, and general observations made during the test did not reveal any appreciable number of dead ants around or in the test colonies. As a result, toxicity was not considered to have any appreciable effect on the results.

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82

PAGE 53

k2 •ri U u CT5 O m Ti o a u o > Pi C O d O 0) o ^ o d •H 03 p « • O 0) 4J •H 03 u bO •H (a3 X -P O C O O •H O d ,d ^ -p >i •H O > w w -p -p d -H CO > U CJ •H -p tH 03 d 0) (U 4J ?-l S-i Pi S s Pi -H a •H Ch O O U 4J d o o I O r-^ a Eh d O •H -P 03 iH O tM -P •H

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^3 o ;3 c •H o o I I ON o CS EH O •H 03 O •H c

PAGE 55

baits to the colony. The poorer control obtained was attributed to the small amount of oil and toxicant available per particle of bait. In order to compensate for thiSj it appeared that either the oil content on the carrier or the concentration of toxicant in the oil had to be increased. The first of these alternatives was investigated in the second test. Formulations of bran were prepared containing l^p, 20fo and 251 byweight of soybean oil. The concentration of Kepone in the oil in each bait was 0.25'fo. Because of the extremely dense growth of grass on the plots, it was impossible to make acciirate counts of mounds at 8 to l6 weeks, so that final coxmt was made after 26 weeks. The data show that the speed of kill with the bait was directly proportional to the amount of oil and toxicant in the bait; however, after 26 weeks, the percent reduction in active mounds was comparable for the three formulations . On the basis of these results, the third test was made to evaluate the 3 carriers in the first test with modifications in the bran and corncob grits formulations to compensate for the small amount of oil or toxicant per particle of bait. Since no satisfactory method had been found at this time to increase the amount of oil on the corncob grits carrier, the Kepone concentration in the oil was increased to 0.5^. It was found that branoil baits could be made containing hO'fo soybean oil. This was done by adding 10';!^ by weight of monoglycerides to the soybean oil. The combination hardened on the bran, resulting in a formulation comparable in oiliness to a 2U^ formulation without monoglycerides. The puffed barley grits formulation remained the same with the exception that 10^ of monoglycerides was added to the oil to retard its seeping from the grits when exposed to the hot sun during and after application to the plots. With the exception of the corncob grits formulation, the

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^5 Kepone concentration in each bait was maintained at 0.25/j of the weight of the oil. The control data (Table 9, Test III) show that all of the baits, including the standard as formulated in this test, gave complete control of the ants. About the time the previous test (No. Ill) was completed, mirex was foiind to be a good toxicant. It was decided to shift emphasis to this compound because mirex was: (l) less toxic to mammals than Kepone, (2) not repellent to ants at high concentrations in the bait, and (3) a little more toxic than Kepone but with good delayed toxic action. Test IV was started to determine the effectiveness of mirex in the soybean oil-corncob grits bait. Concentrations of 0.2y/o and 0.5ya in the oil were tested. The results show that, as with Kepone in the previous experiment, complete control was obtained in 2 weeks at the 0.5)3 concentration. At the 0.25'io toxicant level, complete control was attained also; however, the kill was very much delayed, and the maximum reduction was not reached until after 8 weeks. Test V was initiated to (l) evaluate sawdust as a carrier, (2) retest the corncob grits formulation which had worked so well in the previous experiments, and (3) determine the effectiveness of a corncob gritssoybean oil formulation where the oiliness which occurred at oil levels above 15^ "was overcome by coating the impregnated granules with gelatin. Two levels of mirex in soybean oil (0.25^ and 0.5^) were tested with the sawdust carrier. The source of the sundried pine sawdust was an abandoned millsite near Gulfport, Mississippi. It was sieved through 1/8inch hardware cloth before forra\ilation. The corncob grits-gelatin formulation was prepared by pouring a hot lOfo gelatin-water solution over the oilimpregnated grits as they were tumbled in the mixer. The amount

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of gelatin solution added was 12 I/270 by weight of the corncob grits and oil. The concentration of mirex in the oil on both the corncob grits formulations was 0.5'^. After 16 weeks, the control (see Table 9) obtained with the sawdust formulations was 100^ with the 0.25"^ mirex concentration and S'J'-fo with the 0.5^The corncob grits formulation with the gelatin coating gave slightly better control than the formulation without gelatin (97'/ci vs. 91^ at 16 weeks). In evaluating the k carriers tested on the basis of the criteria listed in the introduction, it was evident that the corncob grits formulations were the most satisfactory with regard to cost, formulation, ease of handling, and ease of application with various types of conventional application equipment. A Comparison of 6 Fats and Oils as Food Att raccants in Toxic Salts for imported Fire Ant Control Peanut oil, tallow, tallow oil, yellow hog grease, and hog grease oil were compared with soybean oil as food attractants when used on corncob grits with the toxicant mirex (0.% in oil). The application rates were 10 pounds per acre. The results are presented In Table 10. After 16 weeks, all the baits had given 100^;^ control except the formulation with yellow hog grease which gave 97°/^ control.

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hi Table 10. --A comparison of 5 fats or oils with soybean oil as food attractants in imported fire ant "baits. (All baits vere made vith corncob grits as the carrier and contained 0.075"/^ mirex in the finished formulation). Fat or oil Soybean oil Beef tallow oil^ Beef tallow't' Yellow hog grease'^ Hog grease oil*-^ Peanut oil Check Average pre-treatraent count of active mounds 13 10 10 12 13 33 12 Percent reduction

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Tatle 11. --The effectiveness of k toxicants in floursoybean oil bait for controllinQ natural infestations of imported fire ants.^ Percent reduction in Avg. pretreatment active mounds after Toxicant and concentration count of active ant following weeks : (fj) in finished formulation mounds 2 4 8 16 Test I ydrex, 0.05 Mirex, 0.1 IIRS-12^3j 0-1 HRS-1243, 0.25 Kepone, 0.25 Check Bayer 309II, 0.02 Bayer 309II. 0.05 Kepone^ 0.25 Check 31

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^9 In Test IIj the plots started to "becorae reinfested after l6 weeks and in Test III^ after 8 weeks. Both these counts were made in Septeniber^ at the time when incipient imported fire ant colonies are most easily found. In addition, there was some migration in Test III of mature colonies across the 50-f'oot buffer zone onto the count areas. For this reason, the best evaluation of the results of these 2 tests can be made by comparing the 2to 8-week resvilts in Test II with the 2to 4-week results in Test III. On this basis, Kepone and mirex at a concentration of 0.075^ both gave complete control. At the 0.1^'fo level, however, mirex gave 100'^ control in Test II and a high of 99^ in Test III compared to 96-^ and 99^0 respectively for Kepone. The lesser control by Kepone at the highest concentration in Test II could be due to greater repellency at this concentration {ifo in the oil). HRS-1243 gave 95^ and 97-/0 control, respectively, at concentrations of 0.15^ and 0.3^^ in Test II and 99^ control at the 0.3^ level in Test III.

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50 Table 12. --The effectiveness of k toxicants in soybean oil-corncob grits bait for controlling natural infestations of imported fire ants. ,

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51 The gffectiveness of Different Application Rates of Corncob GritG-Soybean Oil-Mirex Bail Tests with the corncob grits (85';i)-soybean oil(lij-.925'5i)-mirex(0. 075/3) bait were conducted to determine its effectiveness at application rates varying from 2 l/2 to 15 pounds per acre. After 16 weeks ^ complete control was attained with application rates of 5 pounds per acre and higher (see Table I3). Fair control (52/i) resulted from the 2 l/2-pound rate. Most of the colonies remaining on this plot were affected^ and the following spring only 2 colonies contained brood at a time when colonies on the check plots contained an abundance of brood. The ant infestation in the pasture selected for the test ranged from 13 to 36 mounds per acre. This number is about normal for southern Mississippi. It is possible that higher numbers of colonies per acre might have affected the degree of control at the 5and 7 l/2-pound rates. Other unreported tests have definitely shown that 10 to 15 pounds per acre is sufficient to control infestations as high as 100 mounds of normal size per acre. Table I3. — The effectiveness of a bait composed of corncob grits (85'/j) impregnated with soybean oil (lij-.925/i) and rairex (0.075'w) when applied at different rates per acre.

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52 The Effect of Mirex Concentration and Application Rate on Control of Iraported Jire Ants With Granulated Mirex-Soybean Oil Bait A study was made to determine the effectiveness of granulated mirexsoybean oil bait containing 0.015lo, O.I5/, or 0.3^ mirex and applied at the rate of 3, 5 or 10 pounds per acre. Two complete tests were conducted; one was started in March and the second in June. The results of the preand post-treatment observations on the plots through 16 weeks are presented in Table \h. No counts were made on any of the plots after 16 weeks, because they had become reinfested with new colonies. V/hen this happens, it becomes extremely difficult to distinguish between the remnants of old colonies and the new ones. However, at the l6-week observations, many of the remaining colonies showed symptoms characteristic of toxic bait poisoning; that is, only large workers remained, total worker population was below normal, the mounds were not worked, and no brood was present. In all tests, records were kept of the number of abnormal colonies present at each count period. Continued observation of these colonies has shown that they almost always die. Because of this fact, a percent reduction in active mounds for each treatment was calculated with the assumption that all abnormal colonies present after I6 weeks eventually died. Although this information has little relevancy for small acreage control, it does indicate the potential result if a similar treatment were applied over a large acreage in an eradication program where mating flights into the area would not be a factor. The data show that a very high degree of control of the ant population present at treatment time was obtained on all the plots. There was no distinct difference in control attributable to the 3 different mirex concentrations and application rates with tne possible exception of

PAGE 64

53 0.075/^ mirex bait applied at 3 pounds per acre in J'larch. However, even with this treatment J if all the abnormal colonies died, the eventual control would have been SQ$. There was a marked difference in speed of kill between the March and June treatments. This result was undoubtedly due to temperature differences which have a marked effect on activity of the ants. Table lU.--The effect of mirex concentration and application rate on control of imported fire ants with gramolated mirexsoybean oil bait.^

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^h Control of Imported Fire Ants Folloving Aerial Application Of Granular Mirex-Soybean Oil &^..it to 96O Acres Near Orange Grove, Mississippi The results of the preceding tests definitely show that the most promising bait for large scale applications is the one consisting of soybean oil, mirex and corncob grits. In all cases, it gave high or complete control on small test plots. In addition, it proved amenable to standard packaging, storage and application procedures. To be certain of its effectiveness, however, it was necessary to test the bait over a large area that included a variety of land cover and usage. In addition, its safety to man and animals needed to be verified. To satisfy these requirements, a large scale aerial application was made to a 1 1/2 square mile block of land near Orange Grove, Mississippi. Figure 7 is an aerial photograph of the area indicating the individual subplots where preand post-treatment counts were taken. The bait was applied to the area in September. Post-treatment observations for active colonies were made over a 1-year period with the results for each subplot tabulated in Table I5 and summarized in Table I6. It is evident that the bait treatment was very effective in controlling imported fire ants. At the end of 32 weeks, IOOI0 control had been obtained in all the observation plots except one. On this plot, one colony was found. This colony was not observed on the plot at the 26week count. It is not known whether this was a new colony which had developed after treatment, or an old colony that had not been killed out. It will be noted that the kill of ants was very slow and that even after h weeks, some of the plots showed no reduction in active ant mounds. General observations showed that the greatest effect of the bait was obtained 4 to 8 weeks after treatment. After about 5 weeks of extremely

PAGE 66

55 t o

PAGE 67

56 dry v/eather folioving the application of the baitj thousands of dead ants were found piled up in the road ditches surrounding the test area. The slow kill is undoubtedly attributable to the fact that the test was initiated at the onset of cool weather and to light feeding of the ants on the bait. The light feeding was evidenced by the lack of piles of bait around the ant mounds. Normally, when feeding activity is heavy, small piles of bait from which the ants have extracted the oil are found around the base of the mounds within several days after the bait application. A rapid kill of ants is associated with this behavior. Observations in the test area one year later, showed that it had become heavily reinfested with small ant colonies with mounds ranging from 2-^ inches in diameter. The number of these colonies found on the plots ranged from to 256. Heavy infestations of ants were present in all the surrounding area, providing a ready soiirce of new queens during mating flights. This reinfestation pattern is typical of that noted on small test plots and illustrates the fact that baits offer no residual protection against reinfestation. In general, observations have sho\m that areas treated with bait from January through July most likely will become reinfested the next fall, while areas treated during the latter part of the year will not become reinfested tmtil the fall of the following year. The actual reinfestation in either case appears to coincide with the period of greatest mating flight activity (May-June). It cannot be concluded from these observations that queens from mating flights late in the year will never establish colonies; however, the percentage which does successfully establish a colony is evidently very low. Green (1962) has suggested that large outbreaks of new imported fire ant infestations coincide with periods of frequent showers during June, July and August.

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57 Table 15. --Control of imported fire ants with granular mirex-soybean oil bait on subplots within a 960-acre test area near Orange Grove, Mississippi.^

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58 Table 1^.-Continued

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59 Table l6. — Control of imported fire ants following aerial application of granular mirexsoybean oil bait to a 960-acre test area near Orange Grove, Mississippi.^ Average preNumber of treatment count Land usage observation plots of active mounds Percent reduction in active mounds after following weeks : If c T^ 32 52 Woods

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SUM-IARy AND CONCLUSIONS The imported fire ant, Solenopsis saevissima richteri Forel, was introduced into the southeastern part of the United States during the early 1900's. It spread from the original infestation at Motile, Alabama, into 9 other states encompassing an area of about 100,000,000 acres. Although it causes little direct damage by feeding on plants, its mo\ind building and stinging habits make it an extreme nuisance to both urban and rural dwellers. The research discussed in this dissertation was conducted to develop a toxic bait which could be used for the control or eradication of this pest. Studies were conducted with food attractants, toxicants and granular carriers. The following conclusions are based on the results attained: 1. Most animal and vegetable fats are readily accepted by imported fire ants as food; highly unsaturated fats such as linseed oil, oiticica oil, perilla oil and tung oil are much less attractive. 2. The cost and availability of soybean oil are factors which make it preferable as the food attractant in baits for large scale control programs. 3A once-refined grade of soybean oil is consistently more attractive than a crude grade. h. Kydrogenation of cottonseed oil showed that as the degree of hydrogenation increases, acceptability to the ants decreases. 5. Rancidity causes fats to become less acceptable to ants. 60

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61 6. Tvro a ntioxidants, Tenox 7 and Tenox S-1 did not appreciably decrease the attractiveness of soybean oil at concentrations of 0.05 "to 0.5^ 7. Mirex is an extremely effective bait toxicant. In continuous and limited feeding tests, it gave delayed toxicity over a toO-fold dosage range (0.0025-1'07j) ; in a bait transfer test where 10 major workers were pre-fed and allowed to transfer food to 10 minor workers, it produced toxicity over a 10-fold range (O.l-l.O^). 8. Kepone and HRS-1243 are also effective toxicants, giving delayed kill over a 10to 25-fold range in limited feeding tests. 9. Bayer 3892O, Bayer 30911, coumaphos and 1-fluorochlordene gave delayed kill of ants over a 2to 10-fold dosage range. 10. In bait transfer fests where 20 major workers were allowed to transfer bait to 10 minor workers, mirex killed over a 100-fold dosage range; HRS-I2U3, a ^l-O-fold range; Kepone, a 4-fold range; and Bayer 30911, a 2fold range. 11. In laboratory tests where 20 minor workers transferred bait to 10 major workers, mirex was the only toxicant that satisfactorily killed over a range of dosages (O. 1-1. Op). 12. Puffed barley grits, aged pine sawdust, kenaf or okra hurds , wheat bran and corncob pith or grits are satisfactory carriers for oil baits on the basis of dyed food tests with individual imported fire ant colonies; fresh pine sawdust, vermiculite and several mineral carriers are unacceptable. /13I In dyed food tests with individual ant colonies, mirex was less repellent than Kepone, HRS-1243 and Bayer 309II. Ik. In tests on small field plots, baits consisting of soybean oil

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62 containing rairex or Kepone and wheat bran, cornGO"b grits , puffed barley grits or aged pine sawdust gave control of imported fire ants. 15. Cn the basis of cost, availability , ease of formulation and handling and ease of application with conventional application equipment, the most practical carrier for the oil baits is corncob grits. 16. Soybean oil, beef tallow oil, beef tallow, yellow hog grease, hog grease oil and peanut oil are all good food attractants in mirexcorncob grits baits. 17Mirex, Kepone and HRS-12i4-3 were all highly effective as toxicants in flour-soybean oil baits for controlling imported fire ants in small plot field tests at dosages ranging from O.O5 to 0.25'-/^; Bayer 30911 at 0.05^ gave good control but only fair control at 0.02)j. 18. f-Iirex and Kepone at concentrations of 0.075^ and 0.15'^ in soybean oil-corncob grits baits gave very good control of imported fire ants in small field plots; HRS-I2U3 gave good control at a 0,3/ii concentration but poor to fair control at concentrations of O.OJ^'/o and 0.15^. 19Corncob gritssoybean oil bait containing 0.075"^ mirex gives excellent control when applied at rates of 5 to 15 pounds per acre but poor control at 2 I/2 pounds per acre. 20. Soybean oil-corncob grits baits containing 0.075'/^^ 0.15vi or 0.3;^ of mirex and applied to field plots at rates of 3) 5 or 10 pounds per acre give excellent control of imported fire ants; control of ants is significantly faster when baits are applied during warm summer weather . 21. Aerial application of corncob grits-soybean oil-mirex bait to a 960-acre plot demonstrated that the bait effectively controlled ants in woods, pecan groves, pasture, waste land and crop land (only one colony out of 750 remained on 33 observation plots).

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LITERATURE CITED Adrouny, G. A.;, V. J. Derbes, and R. C Jung. 1959Isolation of a hemolytic component of fire ant venom. Science 130(3373) :^'^9Anonymous 1958. Observations on the biology of the imported fire ant. U.S.D.A. ARS 33-^9Baker, M. F. I963. New fire ant bait. Highlights of Agricultural Research, Agr. Exp. Sta. of Auburn Univ. 10(2) :l6. Barber, E. R. I916. The Argentine Ant. Distribution and Control in the United States. U.S.D.A. Bull. 377Bartlett, F. J., and C. S. Lofgren. I96I. Field studies vith baits against Solenopsis saevissima richteri , the imported fire ant. J. Econ. Entoraol. 5i^-(l) :70-73Bellinger, F., R. E. Dyer, R. King, and R. B. Piatt. 1964. The imported fire ant. A report by the Fire Ant Committee of the Georgia Academy of Science, Inc. U6pp. Blake, G. H., W. G. Eden, and K. L. Hays. 1959Residual effectiveness of chlorinated hydrocarbons for control of the imported fire ant. J. Econ. Entomol. 52(l):l-3Caro, M. R. , V. J. Derbes, and R. Jung. 1957Skin responses to the sting of the imported fire ant ( Solenopsis saevissima ). Arch. Dermotol. 75(4) :475-488. Coarsey, J. M. 1952. Third quarterly report for 1952. Station, Kerrville, Texas, Div. of Insects Affecting Man and Animals, Bur. Ent. and Plant Quar., Agric. Res. Serv., U. S. Dept. Agric. Creighton, W. S. 1930. The new world species of the genus Solenopsis (Hymenop., Formicidae). Amer. Acad. Arts and Sci. Proc. 66(2):87-89. men, v;. G., and F. S. Arant. 1949Control of the imported fire ant in Alabama. J. Econ. Entomol. U2(6) :976-979. Green, H. B. 1952. Biology and control of the imported fire ant in Mississippi. J. Econ. Entomol. 4-5(4) :593-597Green, H. B. 1959. Imported fire ant mortality due to cold. J. Econ. Entomol. 52(2): 34763

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6i^ Green, li. B. 1962. On the biology of the imported fire ant. J. Econ. Entoinol. 55(6) :1003-100i^. Green, II. B. 196?. The imported fire ant in Mississippi. Miss. State Univ. Agr. Exp. Sta. Bull. 73?. Hays, K. L. 1958. The present status of the imported fire ant in Argentina. J. Econ. Entomol. 5l(l) :111-112. Hays, S. B., and F. S. Arant. I96O. Insecticidal baits for control of the imported fire ant, Solenopsis saevissima richterl. J. Econ. Entomol. 53(2) :l88-191. Jung, R. C, and V. J. Derbes. 1957The imported fire ant, Solenopsis saevissima var. richteri, as an agent of disease. Araer. J. Trop. Med. and Hyg. 6(2) : 372373Khan, A. R. I966. Studies on the rearing, biology and control of the imported fire ant. Dissertation State College, Mississippi, 91 PPLofgren, C. S., V. E. Adler, and W. F. Barthel. I96I. Effect of some variations in formulation or application procedure on control of the imr)orted fire ant with granular heptachlor. J. Econ. Entomol. Lofgren, C S., W. A. Banks, and C E. Stringer. 196^1-. Toxicity of various insecticides to the imported fire ant. U.S.D.A. ARS 8I-II. Lofgren, C S., F. J. Bartlett, and C E. Stringer. I96I. Imported fire ant toxic bait studies: the evaluation of various food materials. J. Econ. Entomol. 5i4-(6) :1096-1100. Lofgren, C S., C E. Stringer, W. A. Banks, and P. M. Bishop. I967. Laboratory tests with candidate bait toxicants against the imported fire ant. U.S.D.A. ARS 8l-li^-. Lofgren, C S., C E. Stringer, Jr., F. J. Bartlett, W. A. BanlvS, and W. F. Barthel. 1965. Dual low dosage applications of heptachlor for control of the imported fire ant. Fla. Ent. l4-8(l4-) : 265-270. Mallis, Arnold. 195'+. Handbook of pest control. Second Edition. New York. MacNair-Dorland Company. 1068p. Rhoades, W. C, and D. R. Davis. I967. Effects of meteorological factors on the biology and control of the imported fire ant. J. Econ. Entomol. 60(2) : 55^-558. Travis, B. V. 1939. Poisoned-bait tests against the fire ant, with special reference to thallium sulfate and thallium acetate. J. Econ. Entomol. 32(5):706-713Wilson, E. 0. 1953. Origin of the variation in the imported fire ant. Evolution 7(3): 262-263.

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65 V;ilson^ E. 0., and J. H. Eads. 19^9A report on the imported fire an1: Solenopsis saevissima var. richteri Forel in Alabama. Ala. Dept. of Conservation^ Spec. Rpt. July 16.53PPPl^-^s 13 plates, mimeographed .

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BIOGRAPHICAL SKETCH Clifford Swanson Lofgren was "born July 29, 1925, in St. James, Minnesota, where he lived and attended school until he entered the United States Army in March, 19^6. He worked as a Surgical Technician in the Medical Corps until his discharge in August, 19'+7The next month, he enrolled at Gustavus Adolphus College, St. Peter, Minnesota. He graduated in 1950 with a Bachelor of Arts degree with a major in Chemistry. In 1951, hie was accepted as a student in the Department of Batomology and Economic Zoology of the University of Minnesota and received the Master of Science degree in 195^From 195^ to 1955, he was employed by the Plant Pest Control Division of the Agricultural Research Service of the United States Department of Agriculture on the Golden Nematode Project at Hicksville, New York. In 1955, he transferred to the Insects Affecting Man and Animals Laboratory of the Entomology Research Division of the Agricultural Research Service of the United States Department of Agriculture in Orlando, Florida, where he conducted research on the control of household insects. In 1957, he was transferred to the Plant Pest Control Division at Gulfport, Mississippi, to organize and direct a research program for developing methods of control for the imported fire ant. In 1963, he returned to the Insects Affecting Man and Animals Laboratory, which had moved to Gainesville, Florida, Since then, he has been Project Leader of the Area Control Section of the Laboratory, with

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67 the responsibility of developing methods for outdoor control of mosquitoes , ticks ^ chiggers and other medically important arthropods. Clifford Swanson Lofgren was married to the former Renee Kathleen Liljenberg in 195^ and is the father of 3 children. He is a member of the Entomological Society of America, the American Mosquito Control Association, the Florida Entomological Society and the Florida Antimosquito Association.

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This dissertation was prepared under the direction of the chairman of the candidate's supervisory committee and has been approved by all members of that committee. It was submitted to the Dean of the College of Agriculture and to the Graduate Council, and was approved as partial fulfillment of the requirements for the degree of Doctor of Philosophy. March, I968 Supervisory Committee: Chairman T ^^. /^ /-ts-st/d^h Dean, College of Agriculture D^an, Graduate School

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