TIIE USE OF SEXUAL ATTRACTANT
PIIERDIIIDNES TO INCREASE THE
ADCEPTABIUTY OF THE MALE
CIIEMDSTERILANT 3-DIIIom-Il-PropanedIoI
BY WILD NORWAY RATS
(Rattus mwegm)

Thesis for the Degree of Ph. D.
MICHIGAN STATE UNIVERSITY
RONALD I. FIELD

197 1

_, LIBRARY

Michigan State
University

 

This is to certify that the

thesis entitled

THE USE OF SEXUAL ATTRACTANT PHEROMONES

TO INCREASE THE ACCEPTABILITY OF THE MALE CHEMOSTERILANT
3-Chloro-I, 2-Propanediol

BY WILD NORWAY RATS (Rattus norvegicus).
presented by
Ronald J. Field

has been accepted towards fulfillment
of the requirements for
PH.D. degree in ZOOLOGY

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ABSTRACT

THE USE OF SEXUAL.ATTRACTANT PHEROMDNES
TO INCREASE THE ACCEPTABILITY OF THE MALE CHEMOSTERILANT
3-Chloro-l,2-Propanediol
BX'WILD NORWAY RATS (figtfig§_norvegicus).

By
RONALD J. FIELD

Numerous works have demonstrated the effectiveness of using
sterilization techniques as methods of population control in pest
species. Recently an alpha-chlorohydrin, 3-chloro-l,2-propanediol, which
exhibits permanent chemosterilant properties in Norway rats, 35333;
norvegicus, has been developed by R. J. Ericsson of the Upjohn Co. This
material seems to be virtually one hundred per cent affective in male
rats of this species, if ingested in doses of at least 35 mg/kg. Wild
individuals which encounter the material, however, quickly develop a
severe aversion which may inhibit sufficient food consumption of the
material to induce sterility.

In an attempt to counteract this behavioral mechanism.on the part of
the rats, estrous urine collected from Long-Evans laboratory rats was
mixed with the read containing the chemosterilant prior to introducing it
to the wild rats, thus making it more acceptible to them and increasing
the rate of consumption of the chemosterilant.

The following experiments were performed to demonstrate the
attractiveness of this additive in a series of six tests. 1) Wild-
caught animals were given a 1.0 per cent concentration of the

chemosterilant in their food for a period of six days to determine the

RONALD J. FIELD

severity of bait shyness. 2) These rats were given a similar 1.0 per
cent diet for two days, then three ml. of estrous urine was added daily
to the food containing the chemosterilant in order to determine its
effect as an attractant. 3) Two groups of animals were given a 0.5 per
cent concentration of the chemosterilant in the food simultaneously, but
one group received three ml. of estrous urine daily while the other did
not. #) Several animals were given a 1.0 per cent mixture of the
chemosterilant with the addition of three ml. of estrous urine daily and
results were compared with those obtained from experiment 1. 5) Several
females were separated into two groups. One group was given a 1.0 per
cent mixture of chemosterilant with the addition of three ml. of estrous
urine daily, while the other was given only the 1.0 per cent mixture
without the addition of the urine. 6) A test was made to determine the
existence of synergistic effects between the toxicity of the chemo-
sterilant and a reduction of food consumption by rats.

There are two appendices to this paper. Appendix A involves a
discussion of current rat control techniques practiced in Michigan, and
contains suggestions for possible improvement of these policies.
Appendix B deals with a graphic model of the ecology of rat populations

within an urban ecosystem.

THE USE OF SEXUAL ATTRACTANT PHEROMONES
TO INCREASE THE ACCEPTABILITY OF THE MALE CHEMOSTERILANT
3-Chloro-l,2-Propanediol
BY'WILD NORWAY RATS (Rattus norvegicus).

BY ‘9
Ronald leEield

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Zoology

1971

f‘ ,/ M 3 4/

ACKNOWLEDGEMENTS

I wish to express my appreciation to the following people for their
advice in the preparation of my‘research and evaluation of the project:
Rollin Baker, Hyram.Kitchen,'William.Cooper, and Myles Boylan of'my
guidance committee; John Ruskin and Dr. Dean Tribby of the Ingham Co.
Health Department; Alvin Therrion of the Michigan State Health Department,
and John B. Calhoun, John Christian, Kyle Barbehenn, Charles Southwick,
and William.Jackson, each of whom offered personal suggestions concerning
some aspect of the study.

Additional thanks is expressed to R. J. Ericsson of the Upjohn Co.
who offered several suggestions, and supplied the amount of the chemo-
sterilant which was used in this research.

I am also deeply indebted to several people for funding of expenses
during the time in which this research was being completed. These people
are Rebert Green of the M.S.U. Center for Urban Affairs, w; w; Armistead
of the MLS.U. College of Veterinary Medicine, and James Butcher of the
M.S.U. College of Natural Science.

Thanks are also extended to Anthony P. Miano and Frank Thompson of
the Highland Park Health Department for their assistance in the collection
of rats for the study, and to Beverly Cockrell fer her assistance with
the necropsy of several experimental animals.

A final vote of thanks goes to my wife Sandra for her interest in the
project, and her tolerance of the discontinuity of family life incurred
due to the endeavor.

ii

CONTENTS
Page
INTRODUCTION ....................................................... l
MMHHDES.u.n.u.n.”.u.”.u.u.u.u.n.u.u.u.u.n.u.n 6
MWWSMDMEMMSununuuununnununununuuuu 7
EXPERIMENT I .................................................. 9
EXPERIMENT II ................................................. lO
EXPERIMENT III ................................................ lO
EXPERIMENT IV ................................................. ll
EXPERIMENT V .................................................. ll
EXPERIMENT VI ................................................. 12
RESULTS AND DISCUSSION ............................................. l3
EXPEREMENT I .................................................. l3
EXPERIMENT II ................................................. l7
EXPERIMENT VI ................................................. 21
EXPERIMENT III ................................................ 22
EXPERIMENT IV ................................................. 30
EXPERIMENT V .................................................. 3U
CONCLUSIONS ........ 38
SYNERGISM ..................................................... 38

ACCEPTIBILITY T0 U-5897 TO RATS AS A FUNCTION OF DOSE
CONCENTMTION 0.00.0.0000...OOOOOOOCOOOOOOOOOOOOOOOOOOOOOOOQOOO 39

EFFECT OF USING THE PHEROMONE IN ESTROUS URINE AS AN
ATTRACTANT 0.0.0.0...O...00.000.000.00...0.0.0.0....0.0.0.0.... 39

ATTRACTING.ABILITY OF THE PHEROMONE AT THE 0.5% AS
COMPARED TO THE 1.0% CONCENTRATION ............................ 41

iii

Page
LIIERATIIRE CIIED 0.0.0.0...0.00.00.00.0000.000.000.00.0.00.00.00.00. 1+2
APPENDHA O...OOOOOOCOOOOOOOO...COO...00....OOOOCOOOOOOOOOOOOOOCOOO 48

APPENDHB 0.0...OOOOOOOOOOOOOOOOOOOOOOOOOCOOOOOOOOOCOOOOIOOOOOOOOOO 59

iv

Table

l.

2.

LIST OF TABLES

Daily rate of'consumption of 1.0 per cent mixture of
Up5897 measured in per cent of daily rate of
consumption for normal chicken mash ..........................

Effect on daily rate of food consumption caused by
adding 3 ml. of estrous urine daily ..........................

Daily rate of consumption for 0.5 per cent mixture
of Ua5897 measured in percentage of‘daily rate of
consumption for normal chicken mash ..........................

Comparison of’daily'consumption rates for 1.0 per
cent mixture with and without daily addition of
3m10f eStrmlS urine 0.00.00...0.0.0.0.0...OOOOOOOOOOOOOOOOOO

Effect on daily consumption rate by females for 1.0
per cent mixture of U-5897 caused by the daily
addition of 3 ml of estrous urine ............................

Mean weight loss per individual as a percentage of
original weight 0.00.00.00.00.00000000DOOOOOOOOOOOOOO00.00....

Mean lethal dose of U-5897 per individual ....................

Page

l4

14

24

24

24

20
20

LIST OF FIGURES

Figure

l. Diagram.of three rat pens ....................................
2. Daily rate of food consumption using chicken mash

containing 1.0 per cent concentration of U-5897 ..............
3. Alteration of rate of food consumption caused by

adding 3 ml. of estrous urine on day 3 and 4 to

1.0 per cent mixture or U-5897 00.00.000.000...0.000.000.0000.
4. Daily rate of food consumption for pairs of rats

using 0.5 per cent mixture of U;5897 with and

Without estrous mine added O...O...00.0.0000...OOOOCOOOOOIIO.
5. Daily rate of food consumption fbr single male

rats using 0.5 per cent mixture of U-5897 ....................
6. Daily rate of food consumption for males after

adding 3 ml. of estrous urine to both 1.0 per cent

and 0.5 per cent mixtures of U-5897 ..........................
7. Daily rate of food consumption for pairs of rats

using 1.0 per cent U-5897 mixtures with and

without the daily addition of estrous urine ..................
8. Daily rate of food consumption for females with and

without the daily addition of 3 ml of estrous

urine to 1.0 per cent mixture of U-5897 ......................
9. Model diagram.of'urban rat populations .......................

vi

Page

15

l9

25

31

35

33

36
60

INTRODUCTION & LITERATURE REVIEW

The Norway rat (13291—5. norvegicus) has long been a problem to man-
kind. The species, which is endemic to the Old World, became identified
as a significant health hazard during the Middle Ages when it acted as a
vector for the dread bubonic plague which ravaged Europe during that
period (Zinsser, 1935). Since that time it has become a recognized
vector for some fifty or more diseases.

After being transported to the New World aboard ships of explorers
and merchants (Darlington, 1957: 388), this rodent spread across the
continents following the westward movements of human populations, and
became firmly entrenched as a species and a semiparasite of man.

Presently, this highly adaptable murid rat has been successful in
continuing to be a public health menace especially in cities but also in
agricultural areas throughout the world, in spite of elaborate control
operations. In the United States alone, the estimated total cost of
damages caused by the gnawing teeth and filthy excrements of these
animals lies somewhere between $900,000,000 and $1 billion annually
(Bjornson Q 11;, 1956).

In addition to the simple destruction of property, these animals are
still significant factors in the transmission of diseases and also the
cause of infant mortality and tissue damage to children through the
lacerations and puncture wounds inflicted by their bites (Scott, 1965;

Ruskin, 1968).

Currently, most urban areas in the United States are attempting to
curtail their rodent problems through rat control programs of varying
efficienoy (See Appendix A). Due to the adaptability of these rodents,
and to the relatively inefficient methods of instituted control measures,

the problem persists, and in many instances, is believed to be increasing.

HISTORY OF RAT CONTROL

Historically, man initiated his attempts to control rat populations
through the use of the simple rat traps. These were soon found to be
relatively inefficient. This was mainly due to the rats' high learning
capabilities which lead to the phenomenon of "trap shyness", or the
avoidance mechanism.utilized by rats when encountering traps (Brown, 1960;
Calhoun, 1962a: 88).

The next attempt to control or reduce rat infestations involved the
use of such poisons of the single dose variety as red Squill (Urginea
maritima), strychnine (Stgychnos';p.), arsenic, phosphorus, and more]
recently, alpha-naphthylthiourea (ANTU), sodium fluoracetate (1080), and
flouracetamide (1081). These poisons work to some extent, but again lead
to "bait shyness" on the part of the rats (Bjornson gtflgl., 1965; Brown,
1960). In addition, many of these materials provided dangerous hazards
to nontarget species, including humans, which chanced to come in contact
with them (Ruskin, 1968).

The poisoning procedure was coupled as early as 1913 with more
functional measures such as rat-proofing buildings, garbage removal, and
other environmental manipulations (Simpson, 1913). These practices were
found to be a very efficient combination, but unfortunately, urban

ecosystems were not and are still not compatible with such a program to a

great extent (Calhoun, pers. com.). This is due to several factors, but
can be attributed primarily to building deterioration and housing policy
(Beyer, 1965).

In 1944, Dr. Karl P. Link (Overmann gt 3%., 1944) completed
extensive research on the bovine hemorrhagic sweet clover disease, which
lead directly to the discovery of the multiple dose anticoagulant poisons.
These poisons function very well as rodent control measures, and are still
used today by most authorities. These have several drawbacks, however,
such as the necessity of daily surveillance of the bait material by
personnel. In addition, there is the simple biological fact that merely
killing off adults in an increasing rat population may not be an
effective control measure. This is partially due to the territorial
behavior of the animals, and their propensity for immigration into an
area recently vacated due to mortality (Calhoun, 1961; Davis, Emlem, and
Stokes, 1948; Knipling, 1955). Howard (1967) has theorized that, in fact,
the converse may occur, in that the simple introduction of mortality may
actually cause an increase in density of rodent infestations.

In recent years the advent of antifertility agents (Knipling, 1955,
1960) or chemosterilants offered a new approach to possible control of
rat populations (Bock and Johnson, 1956; Davis, 1961). Theoretically,
this method of control should be superior to simply killing off adult or
even juvenile animals, since lack of mortality in the sterilization
process should result in no immigrational replacement activity.
Conversely, the permanently sterilized dominant animals simply remain,
thus effectively preventing any reproductive recruitment into the

population, and simultaneously inhibiting the immigration of fertile

individuals due to the inherent territorial dominance of those present
(Knipling, 1955).

Conceptually, the idea was highly desirable. Unfortunately, however,
chemosterilants tested were generally found inefficient as sterilants
(Kennelly'gtugl,, 1970), increased bait shyness (Marsh and Howard, 1969) ‘
or caused high mortality rates (Ericsson, 1970). An additional problem
lies in the possibility of sterilization techniques creating an adverse
effect by reducing the dominance and libido of the animals which ingest
it (Howard, 1967; Calhoun, pers. comm.).

One of the latest advances in the field of chemosterilants has been
made by Dr. Ronald J. Ericsson of the Upjohn Company. He has developed
an alpha—chlorohydrin compound (3-chloro—1,2-propanediol) which causes
temporary sterility, permanent irreversible sterility in male Norway rats,
or mortality in both male and.female rats, depending upon the amount
ingested. The drug, labeled U-5897, has been found to be effective in
this manner when administered abdominally, by gavage, mixed in fbod, or
mixed in water (Ericsson, 1970; Ericsson and Connor, 1969). There is a
marked advantage in the drug over many other experimental chemosterilants
due to the fact that only a single dose of'35 mg/kg body weight is required
for permanent sterility. This is a result of the formation of gross
lesions and spermatic granulomata in the caput epididymus caused.by the
action of the drug, thus blocking spenm passage. At a dose level of 152
mg/kg, which has been determined to be the LD-50 dose rate in Norway rats
(Ericsson, 1970), mortality occurs due to the development of lesions in
the myelin sheath of the brain, and also to intestinal lesions and

resultant hemorrhagic gastroenteritis (Ericsson, pers. comm.).

An important quality of the drug is the wide separation (2.5xlO)
between the minimal effective dose (MED) which causes temporary sterility
(6 to 7 mg/kg) and the LD-50 dose. The importance of this fact lies in
the greater likelihood of the target species being able to eat enough of
the material to become infertile, but not ingesting enough to cause
mortality, thereby removing it from the population of territorially
functional male animals.

Ericsson (1970) also notes that the chlorohydrin chemosterilant has
no observable effects in reducing either dominance or libido as have been.1
demonstrated.with other antifertility'measures such as castration.

One of the problems which still exists with this drug is its effect
in causing bait refusal by the animals (Ericsson, pers. comm.). This
would tend to reduce its effectiveness in a wild population since it will
not be consumed in sufficient quantities or by sufficient numbers of
individuals to be effective in reducing the density of the population.

Related entomological problems in attracting insects to traps in
field situations have been partially solved through the use of sexual
attractant pheromones (Roelofs and Coneau, 1970; Brady.gtwgl., 1971).

The effects of pheromones as sexual attractants in mammals have been
noted in canines (Beach and Gilmore, 1949), but no detailed research has
been conducted in that area. Other studies have demonstrated the use of
mammalian pheromones as scent markers (Ralls, 1971), and as influencing
mechanisms in reproduction (Parks and Bruce, 1961; Whitten, 1966; and
Bronson, 1968). The research described in this paper is an attempt to
utilize a sexual attractant pheromone to reduce bait shyness in wild
Norway rats in conjunction with the alpha-chlorohydrin chemosterilants

described above.

OBJECTIVES

In view of the previously stated inadequacies of current rodent
control techniques, the research upon which this paper is based is an
attempt to evaluate a new method. That is to say, it is an attempt to
make a relatively new experimental technique more functional by'making it
more attractive to the rodents themselves.

The method described herein of‘utilizing olfactory sexual
attractants or pheromones to make baits more inticing has been used
previously'in the control of insects (Roelofs and Coneau, 1970; Brady,
gt_al,, 1971). Little however, has been written which concerns the use
of this technique with mammals.

As a supplemental appendix to my basic research problem, I would
like to discuss the current rat control techniques as they are practiced
in various cities in southern Michigan and attempt to suggest possible
alterations or additions which might improve these existing techniques.
These proposed suggestions will include additional methods of enumerating
rat populations and a discussion of rodent breeding seasons which could
lead to better evaluation of control efforts and to perhaps a more
efficient reduction in populations through better synchronization of
these control efforts with reproductive periods.

A second appended supplement to this paper will involve a graphic
model which describes the ecological interactions of a rat population
within the biological framework of an urban ecosystem. This graphic
representation will be discussed at length for additional clarification

of its structure.

METHODS AND MMTEREALS

Forty-five wild Norway rats were caught in Tomahawk and National
‘Wire live traps from various locations in the greater Lansing, Michigan,
area, to be used as the experimental subjects for the testing of
pheromones as attractants with chemosterilant baits. After capture,
these rats were housed in quarantine cages prior to being placed in
3' x 6' experimental pens for the actual testing (Figure l).

The experimental pens were constructed from 3/4" plywood sheets
which were 4' in height. The lower 16" of all four sides of these pens
were lined with 22 gauge galvanized sheet metal as a preventative measure
against gnawing by the rats. All of the pens were kept on a light cycle
of alternating twelve hours of light and twelve hours of darkness. The
ambient temperature was regulated at 70°F.

Each pen was supplied with an unlimited quantity of water. Food was
provided in the form.of chicken feeder mash which was placed in 4” diameter
finger bowls. The mash was used in preference to prepared lab rat chow
in the form of nuggets, in order to prevent the animals from.removing it
from the feeding dish and storing it for later consumption (Marx, 1951).
The enclosures also contained one galvanized tin nest can for each rat
present in the pen, and an additional wooden nest box. The floors of the
pens were covered with wood chips for sanitation purposes, but this
material was only changed at the end of the testing period for each rat
or pair of rats. The subsequent cage litter soiled by only that animal
or pair of animals was allowed to accumulate in an attempt to increase or

maximize the familiar home range or territorial behavior among the animals

(Belle, 1971).

FIGURE 1:

1 BLOCK OP 3 RAT PENS

48" 286 IN EACH
CORNER

 

2 HINGBS
PER DOOR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Several types of experiments were conducted upon these wild rats in
order to determine the effects of estrous urine from female laboratory
rats in attracting wild rats to a chemosterilant bait.

The estrous urine used in the experiments was collected from female
Long-Evans laboratory rats, in accordance with suggestions offered by
John B. Calhoun (pers. comm.). Metabolic cages which separated and
caught both the urine and the feces of the animals within them were used
for the collection of this material. I

The stage of the estrous cycle in the lab rats was determined daily
by taking vaginal smears following the procedure outlined by Zarrow
(1964). Only females actually in estrous, i.e. having cornified
epithelial cells present in vaginal smears, were used for the daily
collection of urine. Urine from all such females was mixed together and
was used only on the day it was collected. Any unused portion was
discarded rather than stored for use at a later date, thus preventing any
possibility of decomposition of the hemical structure of the pheromone

material due to aging.

Experiment I:

Fourteen adult rats consisting of six pairs and two single males
were given a diet of plain or untreated normal mash for five days to
determine their average daily food consumption. At the end of this
period, the animals were weighed. The normal food was then replaced with
a homogeneous mixture prepared by the Upjohn Company and obtained through
the cooperation of Dr. R. J. Ericsson. This mixture consisted of the
same chicken feeder mash but had the addition of 1 per cent by weight,

U-5897. The animals were kept on this diet for five days in an attempt

10

to determine their acceptance of this material as food, and to determine
their average daily consumption of the mixture. At the end of the
experimental period all dead animals were weighed and examined to
determine cause of death and the effects of the chemosterilant. This
became standard procedure for each of the experiments, as did the initial
several day diet of plain mash, and the recording of weights at the end

of this period.

Experiment II:

Ten adult rats consisting of one single male and feur pairs from
Experiment I and one new single male were tested with a 1.0 per cent
mixture of U-5897 after a 10 day average was taken fer normal food
consumption. The animals were placed on a diet of the 1.0 per cent
mixture for two days, and the average consumption was calculated for this
diet. At the end of this period, three ml. of estrous urine were added
to the 1.0 per cent mixture of chemosterilant daily for two additional
days, and the average consumption was again determined for the food.with
the pheromone added. This experiment was a preliminary attempt to
evaluate the relative efficiency of estrous urine as an attractant when
mixed with bait material which had been previously demonstrated to be

undesirable to rats (Ericsson, pers. comm.).

Experiment III:

Twelve adult rats (four pairs and four single males) were once again
given normal food for five days. On the sixth day, the normal food was
replaced with the mixed chemosterilant bait, but the concentration of
U-5897 was reduced from the previous 1.0 per cent to 0.5 per cent by

weight. These rats were separated into two equal groups of two pairs and

11

two single males each. One group was then given only the 0.5 per cent
chemosterilant mixture, while the other was given the same mixture, but
with the daily addition of three ml. of estrous urine. The results of
this experiment were graphed to determine any difference in the rates of

food consumption between the two groups.

Experiment IV:

Three pairs of adult rats were tested.with a 1.0 per cent mixture of
the chemosterilant and the daily addition of two ml. of estrous urine.
The average daily rate of consumption of this mixture was then compared
with the results of the paired animals from.Experiment I in order to
determine the effect of the pheromone as an attractant at a 1.0 per cent

concentration of chemosterilant.

Experiment V:

Five single females were tested at the l per cent concentration of
the chemosterilant mixture after their normal fOOd-consumption average
was determined. Three of these animals were then placed on the plain 1.0
per cent mixture, while the two were placed on a diet of the same mixture,
with the addition of three ml. of estrous urine daily; Although 3-chloro-l,
2-propanediol has no effect as a sterilant on female rats, it has been
shown to be lethal to them when ingested in quantities equal to or in
excess of the LD-5O dose rate of 152 mg/kg body weight (Ericsson, 1970).
Fer this reason, it becomes important to determine whether female rats
are also attracted by the pheromone in estrous urine if it is mixed into

a chemosterilant bait.

Experiment VI:

.After tabulating the results of the original five experiments, it

became apparent that differential mortality occured between groups of
animals that ate relatively large quantities of the chemosterilant and
then ate little or no food afterward, and other groups which ate as much
or more of the chemosterilant but ate a great deal of supplemental food.
I proposed the hypothesis that food acts as somewhat of a buffer, thus
delaying the lethal effects of the drug when large amounts of food are
eaten with the chemosterilant. In order to test this hypothesis, the
following experiment was devised and instituted.

Eight adult male Long-Evans rats were separated into 2 groups (Group
A and Group B) which contained 4 rats each. Each group was given an
unlimited supply of drinking Water for the duration of the experiment,
but all animals in Group A were denied all food from the date of initial
injection until they died.

Group A was then split into 2 sub—groups, A—1 and A—2, each of which
contained 2 animals. The animals in A-l then received gavage doses of
the U—5897 chemosterilant at the rate of 200 mg/kg on the first day, and
100 mg/kg on the following day; After this injection of 300 mg/kg, the
animals were simply allowed to remain in their cages until they died.

The length of this period was then recorded for comparison with Group B.

The animals in A-2 also received 300 mg/kg of the U-5897 in the same
manner, however, they were injected at a rate of 75 mg/kg/day fer the
first four days of the experiment. Their survival time was also recorded.

Group B was treated identically with Group A except that an unlimited
supply of food was made available to the animals, and their individual
daily food consumption was recorded. At the conclusion of the experiment,

results from all four sub-groups were compared.

RESULTS AND DISCUSSION

Experiment I: Results

The daily'average food consumption of normal chicken mash was
calculated to be 25.2 t 1.6 grams per day fer each individual rat tested
in this group. For convenience and accuracy, the animals which were
paired in pens were considered as a unit, and the unit or pair
consumption averaged 50.2 i 3.3 grams per day for the trial. This
overall average food consumption was then broken down into the individual
components which were found to be 24.1 i 3.6 gms/day for males and 19.2 i
5.1 for females (see Table 1). This computation was performed by
calculating the ratio of the individual weights of each animal to the
total weight of both animals in the pen. The total consumption of food
per day'was then multiplied by this fraction to determine the number of
grams of food eaten by each animal. This method assumes that the rate of
food injection per gram of rat is a constant.

All figures which refer to the rate of consumption of food for the
animals being tested with the U;5897 will be stated in terms of a
percentage of the normal daily rate of food consumption. This method
eliminated any discrepancies in the absolute amounts eaten in grams,
which are obviously functions of the sizes of the individual animals.

All data include 95 per cent confidence intervals in the standard errors
of the means.

on the first day of the introduction of the chemosterilant in the
food during this experiment, food consumption dropped drastically for
both the pairs and the single males (see Table l and Figure 2). On the

second day of the test, the consumption continued to drop to less than

13

14

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omocwm m>xwfim MHNm ow>2m Awooww aHazmca :szm Ncumc u ea cmeMI>mdmc U>Hra
H N u e
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mHzorm x>rmm z I N n I wo.H H ~.m o.o o.o w.u H o.o u.m H o.o

 

 

0.1

100.0

.10.0

0’

fl

—
.-
‘-
—

 

 

15

FIGURE
DAIL or FOOD CONSWPI-ION
us INC CHICKEN MASH CONTAIN c
1.0 PER CENT CONCENTRATI
0F U-5897
SINGLE MALES
PAIRS ------
( 95 CON ENC LIMITS ARE 1- 5 1
ON DAY 1 AND .0 FOR ALL

16

l per cent of normal, and remained there for the remainder of the testing
period. There was possibly a somewhat greater effect upon single males
than on paired animals; however, this could not be verified statistically
due to the small sample size.

The lethal doses in Experiment I averaged 4453 i 9.5 gms/animal for
each of the three males, and 45.0 i 10.0 for the two females which died
during the test period. This was approximately 122 mg/kg for these animals.
The survival times for the animals which ingested lethal amounts of the
chemosterilant were calculated to be 4.7 i 0.3 days for the males, and
4.5 i 0.5 for the females.

Post mortem.examination with the assistance of Dr. Beverly Cockrell
showed that each had died due to severe intestinal hemorrhaging or
gastroenteritis and acute dehydration along with depletion of all body
fat. All males tested had developed bilateral lesions in the epididymus,
and exhibited bilateral atrophy of the testes. Lesions in the cranial
myelin sheath similar to those found'by Ericsson (pers. comm.) were
sought but were not found in any of the rats examined.

At the end of the sixth day of the treatment with the chemosterilant,
the remaining nine rats of the original group of 14, were returned to a
plain mash diet. Since five cases of'mortality had already occurred, thus
making a prediction of the effect possible for the remaining rats, it was
deemed more feasible to utilize these surviving animals as test subjects
in Experiment II than to kill them at this time. This provided a supply
of rats which were preconditioned or presensitized to the chemosterilant
and therefore exhibited severe bait shyness.

0n the first day of replacement of the 1.0 per cent mixture of

U;5897 with normal or untreated.mash, the fecd consumption immediately

17

increased to an average of 26.76 grams per individual. This represented
an increase of nearly 2 grams over the original rate of consumption before
the chemosterilant was introduced. These findings using wild rats are in
contrast to those of Ericsson (pers. comm.) who found that when laboratory
rats were treated similarly, their rate of consumption at the time of
reintroduction to untreated food remained at a low level, and did not

return to the original level for some time.

Experiment I: Discussion

The data gathered on these animals apparently demonstrate that after
an initial ingestion of about 40 mg of the U-5897 (see Figure 2) per
capita, when present in food at a 1.0 per cent by weight concentration,
the rats developed extreme anorexia and refused to eat any more of the
food containing this material. This is the phenomenon described
previously'by Calhoun (1962a) as bait shyness. In the case of five of
the rats, this behavioral phenomenon was continued to the point of death.
If the rest of the experimental animals had been allowed to remain on the
same diet over a longer period of time, it can be predicted fromrthe
results obtained for those original five animals that the rest would also

have died from similar causes.

Experiment II: Results

At the end of a ten day ‘recuperation period from.Experiment I, the
nine remaining animals along with one new male were placed on a diet
containing 1.0 per cent U-5897. The average consumption of normal food
had been previously'calculated to be 51.5 i 4.4 for pairs and 30.1 i 1.8

for single males.

18

The rate of food consumption dropped drastically at the first
contact with the chemosterilant. The new male, however, which had not
been presensitized to the material, only dropped to 12 per cent of normal
on the first day, as compared with a far greater reduction in the case
of all other animals (see Table 2, Figure 3). .After a second day of very
low consumption by all animals, 3 ml of estrous urine from the laboratony
rats of the Long-Evans strain was added to the food containing the 1.0
per cent concentration of U;5897. This resulted in a sharp increase in
food consumption in both pairs and single males (see Table 2 and Figure 3).
The pairs increased their consumption to 8.4 i 2.8 per cent of normal
while the single males were somewhat lower at only 5.3 i 0.6 per cent of
normal. On the following day, each group continued to increase. The
pairs climbed to 14.4 i 5.6 per cent and the single males to 7.5 i 0.0
per cent.

At this point, all animals were terminated for necropsy, and per
cent weight loss was calculated for both male and female animals (see
Table 6). Males were calculated to average a 13.5 i 3.0 per cent weight
loss, while females were recorded as averaging 12.2 i 1.5 per cent.

The results of the necropsy were the same as those from Experiment I.
All males had developed bilateral testicular atrophy. All animals
exhibited some intestinal enteritis, although it had progressed to
mortality in the case of only one male which died on the third day of the

experiment.

Experiment II: Discussion
This experiment, like Experiment I, was a pilot experiment. It was
designed to determine the effect of the estrous urine collected from.Long-

Evans laboratory rats when added to an undesirable food material for the

100.0

10.0

PER CENT

OF NORMAL
RATE OF

CONSUMPTIO'

1.0

I'YS

 

 

 

19

FIGURE 3:

ALTERATION OF RATE OF
CONSUMPT CAUSED BY ADDING
ESTROUS URINE ON DAY

PER CENT
MIXTURE OF U-5897

CE LIMITS ARE:
4.2 FOR PAIRS

0.3 FOR SINGLE MALES

20

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21

purpose of'making it more attractive to Wild Norway rats. The results
accrued from this experimental manipulation of the food material
apparently demonstrate that the estrous urine is indeed an effective
attractant. This seems to be verified by the more than 500 per cent
increase in mean food consumption rate which is induced by the addition
of the urine.

This experimental addition of urine apparently caused no detrimental
effects in the chemosterilant properties of the Ue5897, since the male
rat which was introduced to the chemosterilant for the first time during
this test, developed bilateral lesions and testicular atrophy to a similar
degree as those animals which had been preconditioned with up to 65 mg of

the material in Experiment I.

Experiment VI: Results

In order to facilitate clarity in the discussion of Experiment III
through Experiment V, the results of Experiment VI are interjected at
this point, rather than in the normal sequential position.

After initial injections of the 1.0 per cent water solution of the
U-5897, it was found that the animals getting the 300 ml in two days died
on the third and fourth days after this initial injection. They had
averaged a weight loss of 7.3 i 0.8 per cent of their original weight.
The animals, which were given similar doses in the same two day period
but had supplemental food which they ate at a rate of 1.6 grams per day
each, lived for three and six days after initial injection.

The weight loss for this second group of animals was also found to
be somewhat lower than in the first group, being 6.15 i 1.15 as compared

to the previous 7.3 i 0.8 per cent.

22

When comparing the animals which received the lethal dose at a rate
of 75 mg/kg/day for four days, similar results occurred. Those which
were permitted to eat nothing after injection, died on the sixth day
after initial injection, and had lost an average of 33.45 i 1.35 per cent
of their normal weight. Those which were supplied with all the food they
wanted to eat (an average of 10.9 grams per day per individual throughout
the experimental period) were simply terminated at the end of nine days
since they showed no sign of expiring. They had only lost an average of
11.25 i 0.35 per cent of their original weight, or an average of 65.4 per
cent less weight than the rats which did not receive food and therefore

died quite rapidly.

Experiment VI: Discussion

This experiment was designed to evaluate the possibility of the
existence of synergistic effects brought about by a lack of food coupled
with ingestion of relatively large amounts of the toxic chemosterilant
material. This theory would explain the difference in LD-5OS recorded in
the original set of experiments I through V. The results from Experiment
VI indicate that synergistic effects are incurred if both conditions are

met simultaneously.

Experiment III: Results
Group A: Pairs of animals without pheromone

Reactions exhibited by the two pairs of animals in this group when
the chemosterilant was first introduced into their food at a 0.5 per cent
concentration, were similar to those in the previous tests. On the first
day of contact with the food mixture, the rate of food consumption in

these rats drOpped to 25.1 i 1.3 per cent of the normal rate of 40.7 i 3.5

23

grams per day per pair. 0n the second day the rate dropped to less than
2 per cent of their normal rate (see Table 3 and Figure 4), and remained
at that level for the following day. On the fourth day of the testing
period, food consumption increased sharply, rising to a level of 21.6 i
21.4 per cent of normal. This rate then continued until the eighth day
of treatment, when all animals in the group were dead. None of the
animals in this group died before the end of the seventh day of treatment.

The average lethal dose ingested by these animals was calculated to
be 418.1 1 96.9 for the males, and 396.1 1 216.3 for the females in the
group. This total ingested dose of the chemosterilant was observed to be
eaten in two major peaks. These occurred on the first day of the treat-
ment, and then on the fourth through the final days of the experiment.
Arithmetic computations demonstrated that an average of 222.0 i 22.7 mg/kg
were eaten by each pair before the sudden rise in consumption on the fourth
day of treatment, of which an average of 89.4 per cent of this amount was
eaten on the first day of the trial.

The apparent bait shyness, which immediately followed initial
ingestion of the material on the first day of the trial, was probably due
to a mild intestinal enteritis and irritation of the mucosa due to drug
action. On the fourth day, however, the animals probably simply became
hungary enough to overcome the bait shyness, and began to eat enough of
food to sustain life, at the same time ingesting enough to poison them-
selves. This hypothesis can be partially supported by the amount of
food, in grams, which was eaten by the individuals. After the first day,
the rats ate only an average of 1.5 per cent of the normal consumption
rate, or less than 0.3 grams of food per day per individual. This rate

was maintained for both the second and third days of the test period.

24

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100.0

PER CENT
OF NORMAL
RATE OF
FOOD
CONSUMPTIONW

10.0 ‘-

 

1.0 fl
DAY

ha»-

25

VIII—'-

FIGURE 4:

DAILY RATE OF FOOD CONSUMPTION
FOR PAIRS 0F RATS USING 0.5 PER
CENT MIXTURE 0F U-5897 WITH AND
WITHOUT ESTROUS URINE ADDED

WITH URINE ------
WITHOUT URINE

 

Z CONFIDENCE LIMITS ARE:
3.1 WITH URINE
9.5 WITHOUT URINE

9

U‘

i
i

26

Results of necropsy showed the same characteristics in these animals
as in those from Experiments I and II. All animals had died as a result
of extensive gastroenteritis and severe dehydration. All males in the
group showed bilateral epididymal lesions and testicular atrophy. The
weight loss for these animals was calculated to average 23.2 i 3.1 per
cent for the males and 19.5 i 10.2 per cent for the females.

Group B: Pairs of animals with pheromone

This group of animals reacted to the material in a highly
contrasting manner to those in Group A, in that they did not exhibit as
great a reduction in food consumption. The initial drop on food
consumption to 21.1 f 0.3 per cent was similar to the drop in the animals
which did not have the additive pheromone attractant, but, there was no
subsequent drastic reduction on the second day of the treatment (see
Table 3 and Figure h). Instead, an average of 18.8 per cent of normal
was maintained throughout the entire experiment until all animals had
died on the sixth day of the trial.

This was again in contrast to Group A since all of the animals in
Group B died on or before the sixth day of the trial, which was one day
earlier than those without pheromone. This could quite probably be
‘accounted for by the much higher total ingestion of the chemosterilant at
an earlier date by those with pheromone attractants.

The animals in Group B all died from an average lethal dose of 420.9 1
125.7 mg/kg, which had been ingested by the sixth day, as compared to a
lethal dose for Group A of #12.1 i 156.6 which was not attained until the
seventh day of treatment in that group.

The results of the post mortem examination on these animals were

similar to all previous results. Bilateral epididymal lesions and

27

testicular atrOphy along with acute gastroenteritis were present in all
animals in the group. 'Weight loss was calculated to be 27.7 i 5.0 per
cent for the males, and 17.3 i 9.8 for the females.

Group C: Single males without pheromone

The animals in this group were found to react in a similar manner to
those animals in Group.A. Food consumption plunged to an average of 9.6
per cent of normal in the second day of treatment, after an initial drop
to 17.7 per cent of normal on the first day (see Table 3 and Figure 5).
It remained at approximately 9 per cent for the third day, and then
increased to 23.7 per cent on the fourth day as did the consumption rate
in Group A. This rate was then maintained until death on the seventh
day, just as was the case with the animals in Group A.

The lethal dose was found to average #40.0 1 120.5 for these
animals, and their weight loss was calculated to be 25.2 i 1.7 per cent
of the original weight.

Group D: Single males with pheromone

These animals were found to be quite similar to those in Group B and
greatly in contrast to those in Group C. Once again, the average
consumption dropped drastically to 22.0 i 1.0 per cent of normal on the
first day of treatment, but rather than continue to drop on the second
day, it rose from that level to 25.8 i 16.9 per cent. The rate then
began to tail off gradually as the animals apparently'became quite
severely affected by the U-5897. All animals were dead by the sixth day
of treatment.

The lethal dose ingested by these animals was calculated to be
429.8 i 150.3 Per individual, and their weight loss was found to average

19.9 t 0.2 per cent of the original weight.

28

The results of necropsy were again similar. All animals were found
to be severely'dehydrated, exhibited acute gastroenteritis, and the males
were permanently sterilized in the same manner as all previously examined

animals.

Experiment III: Discussion

This experiment was designed to answer four separate questions.

1. To determine whether there was a difference in acceptance of baits by
rats when there was no pheromone added to the chemosterilant bait mixture,
but the concentration of U-5897 was reduced from 1.0 per cent to 0.5 per
cent. 2. To compare the effects of using the pheromone as an attractant
at the 0.5 per cent concentration, with the effects of using the same
addition of pheromone at a 1.0 per cent level as previously recorded in
Experiment I. 3. To determine if the pheromone actually created better
bait acceptance in animals whose food was treated with the substance,
when compared with animals which were simultaneously given identical food
material, but without the pheromone additive. h. To demonstrate any
differences in the attractant ability of the pheromone in regard to single
males when compared to males which were mated to females.

1. The question concerning the difference in bait acceptance
between the 1.0 per cent and the 0.5 per cent concentrations of the
chemosterilant without the additional presence of any attractant is quite
clearly answered by this experiment. In the case of the 1.0 per cent
concentration, the daily rate of consumption dropped below 0.07 per cent
of normal (see Figure 2), and stayed at that level until the termination
of the experiment. In the case of the 0.5 Per cent concentration, the
food consumption never dropped as low as 1.2 per cent of normal, or more

than 17 times higher than that of the 1.0 per cent concentration. At the

29

end of only two days of less than 2 per cent of normal consumption rate,
that rate rebounded to more than 21 per cent and then averaged 19.2 per
cent of normal for the remainder of the trial period (see Figure 0). It
therefore appears evident that a mixture of 0.5 per cent concentration is
highly'more acceptible to wild rats than is a mixture of 1.0 per cent
concentration of the U-5897.

2. The determination of the differences in the attractive ability
of the pheromone when added to a 0.5 per cent mixture of U-5897 as
compared with the same pheromone when added to a 1.0 per cent mixture can
be Obtained when the results of Experiment IV are studied. These results
will be discussed at length later in this paper.

3. The comparison between the groups of animals (A & C) which
received food containing the 0.5 per cent concentration of the U-5897 and
the groups (B & D) which received the same food with the addition of‘3 ml.
of estrous urine daily, points to a probable positive attractive
influence exhibited by the estrous urine. The rather drastic increase in
food consumption on the fourth day by all animals on a diet which did not
include the pheromone attractant can probably be attributed to a
combination of three factors. First, these animals had not eaten enough
of the chemosterilant on the first day to cause them to be irreversibly
poisoned. Secondly, they had eaten enough food on the second and third
days of the experiment to keep from losing strength and thus creating the
synergistic effect of the U-5897 as previously discussed in Experiment VI.
Thirdly, the animals while ingesting enough food to inhibit synergism.for
2 days had eaten far below their normal rate of consumption, and were
reaching a level of extreme hunger at this point, thus highly influencing

their return to the food. It must be noted that in Experiment I, none of

30

these phenomena occurred.i,g, the animals had already eaten enough of the
chemosterilant to have lethal effects, or at least, they had eaten enough
to make them so sick that the bait shyness was permanently'established.
In addition, these animals ate little or no food during the final five
days of the experiment, and thus apparently fell victim.to the combined
effects of the drug and the lack of food.

4. The success of the pheromone as an attractant when used with
single males as compared to mated males is demonstrated by Figures 4 & 5
and Table 3. The difference can be seen by comparing the rates of daily
food consumption for each of the test groups. Mated.males average some-
what higher overall with the average consumption of pheromone treated
chemosterilant material being 21.5 i 3.7 for mated males and 16.0 i 6.2
per cent of normal for single males. Due to the rather large standard
errors and the small sample size, the rates could not be statistically
verified to be significantly different, although it is possible that
paired males may have been more attracted to the pheromone than single

males were.

Experiment IV: Results

The three pairs of animals which were given the 1.0 per cent
concentration of the chemosterilant in this test were compared with the
animals in Experiment I to determine the effect of the pheromone as an
attractant at the 1.0 per cent level.

It was found that these animals with the pheromone attractant dropped
in rate of consumption to 14.2 per cent of normal for the first day of
the trial, and then averaged 5.6 per cent for the remaining six days of

the experiment until all animals were dead by the seventh day.

31

 

 

 

 

 

 

 

FIGURE 5:
-1
DAILY RATE OF FOOD CONSUMPTION
FOR SINGLE MALE RATS USING 0.5
PER CENT MIXTURE OF U-5897
WITH ESTROUS URINE ------
WITHOUT ESTROUS URINE
957. CONFIDENCE LIMITS ARE:
1 6.0 mm URINE
: 4.6 WITHOUT URINE
PREDICTED SMOOTHED CURVE
WITH ESTROUS URINE - —-—- -
100.0
PER CENT OF
NORMAL RATE
OF FOOD
CONSUMPTION
10.0 .—
1.0 ~L..__,_,w,ml _,‘__m__ ' M 1 p p 1 1 \
ms "*1 ‘ “‘5'“ *3 “I y" 7,

32

Necropsy results were again similar to all other experiments, in
that all animals exhibited severe hemorrhaging of the intestine and
stomach, and all males had developed epididymal lesions.

The average per cent weight loss was calculated to be 22.6 i 0.0 for

the males and 22.6 i 2.3 for the females.

Experiment IV: Discussion

When compared with animals which had received the same concentration
of chemosterilant in their food for the same length of time, it appears
that these animals which had the pheromone attractant added to the food
found it far more acceptible than those in Experiment I which had no such
additive. The original drop was slightly greater for the animals which
had the pheromone present (14.2 per cent of normal as compared to 19.2
per cent for the other group). After the first day of treatment however,
there was a very significant difference in the amounts of food eaten by
each of the two groups. Those animals without pheromone averaged only
0.22 per cent of normal per day, and during three of the final six days
of the experiment, they ate no food at all. This is contrasted.with the
animals in the group with pheromone additive. These animals never
dropped below 4.9 per cent of normal, and averaged 5.6 per cent for the
final six days of the experiment (see Figure 7).

In addition to the simple rate of food consumption, the lethal dose
was considerably higher for these animals than for those which did not
eat and subsequently developed synergistic effects between the action of
the U-5897 and the lack of food (see Table 7). The animals without the
attractant died after eating approximately'122 mg/kg of the material

while these animals ate an average of 355.7 mg/kg before dying.

100.0

10.0

DA YS

)—

33

FIGURE 7
ILY TE op moo ONSUMPHON FOR
PAIRS F RATS USING 1.0 PER CENT
U~5897 MIXTURES WITH AND WITHOUT
THE DAILY 4001 on o ROUS URIN
ROUS URINE \

tumour ESTR s URIN ------

952 CONFI cs LIMITS ARE-

1 1.6 WITH URINE

i 1 0 ~er ur URI

34

A third comparison can now be made by evaluating the effectiveness
of the pheromone in attracting male rats to a 0.5 per cent concentration
of U-5897 with its effectiveness in attracting male rats to a 1.0 per
cent concentration of U—5897 in food material. It can be demonstrated
(see Figure 6) that the food consumption rate for animals which were given
the 1.0 per cent concentration of the U-5897 which was treated with the
pheromone attractant averaged only 6.8 per cent of their normal daily
rate of food consumption over a 7 day period while those animals which
were given the pheromone as an attractant to a 0.5 per cent concentration
of the chemosterilant, ate 21.5 per cent of their normal rate on a six
day average. This would seem.to point toward a stronger attraction of

the pheromone if used in a 0.5 per cent mixture of the chemosterilant.

Experiment V: Results

The two groups of female rats which were tested at the 1.0 per cent
concentration level were found to react very favorably to the pheromone
attractant if it was added to the food mixture. The rate of food
consumption for the animals without the pheromone dropped to 6.5 per cent
of normal on the first day of treatment, and then stayed at a similar low
level (see Table 5 and Figure 8). In contrast, the females which had the
pheromone additive dropped only to 14.2 per cent of their normal rate of
food consumption on the first day, and then began to climb until they
reached 106.0 per cent of their normal consumption on the fifth day of
the test. At this point, they rapidly tailed off and all animals died by
the seventh day of the test. The animals without the pheromone never
reached as high as 10 per cent of their normal consumption rate, but due
to their continual ingestion of small amounts of food daily, they

continued to survive until the eighth day of the test.

 

135

 

100.0
FIGURE 6:
DAILY RATE OF FOOD CONSUMPTION FOR
\ MALES WHILE ADDING 3 M1. OP ESTROUS
URINE To BOTH 1.0 PER CENT AND 0.5
\ PER CENT MIXTURES 0P U-5897
0.5 PER CENT MIXTURE ______
1.0 PER CENT MIXTURE ------
‘ 952 CONFIDENCE LIMITS ARE:
1; 6.0 for 0.5 PER CENT
\ i 1.6 for 1.0 PER CENT
10.0 1
PER CENT
OF NORMAL -”T‘
RATE OF ‘\.\\
FOOD
CONSUMPTIOT \”' ‘\\__..__.__..,—— —-' “~ ...‘_
1.0 -
0.1 ‘L j1 l 1 _*l
I T —T —"'
DAYS 1 2 4 5 6 7

100.0 _‘

PER CENT OF
NORMAL RATE
OF FOOD

CONSUMPTION

10.0 .1

136

FIGURE 8:

DAILY RATE OF FOOD CONSUMPTION FOR
FEMALES WITH AND WITHOUT THE DAILY
ADDITION OF 3M1 OF ESTROUS URINE T0
1.0 PER CENT MIXTURE OF U-5897

WITH ESTROUS URINE
WITHOUT ESTROUS URINE ------

95% CONFIDENCE LIMITS ARE:
1 10.4 WITH URINE
1 7.8 WITHOUT URINE

 

 

1.0

1

DAYS

r’
2

 

37

The lethal doses were calculated to be 1044.7 i 685.4 for the
females with the pheromone, and 450.0 1 251.0 for the females without any
attractant. These figures are far greater than those for male rats on
similar concentrations, and also nearly 700 per cent of those stated by
Ericsson (1970) as being the LD-50 dose rate for lab rats.

Once again, necropsy showed that the animals had died from a
combination of dehydration, loss of body fat, and extreme gastroenteritis.

weight loss was calculated to be 25.6 per cent of the original
weight for the animals with pheromone, and 24.4 per cent for those which

were without any attractant.

Experiment V: Discussion

This experiment demonstrated that females are attracted even more
than males to the estrous urine of laboratory rats, and thus, that the
pheromone is a highly successful attractant for females when used in
conjunction with the alpha-chlorohydrin chemosterilant. Although the
compound is not effective in sterilizing female rats, the information may
be valuable for future use because females may be expected to possibly
eat enough of the material to be lethal to them. In certain wild
situations they may also deprive males of enough of the material to be
effective against them in the chemosterilant fashion in which it was

intended. This possibility however, must be more thoroughly tested.

CONCLUSIONS

As previously stated, the basic purpose of this paper is to
determine the relative efficiency of using the estrous urine from
laboratory rats as an attractant to induce wild male Norway rats to
ingest an undesirable chemosterilant poison.

In addition to supplying data concerning this question, this series
of experiments has also suggested several properties of the alpha-

chlorohydrin material which were not previously described.

SYNERGISM

From.the results of Experiment VI, it appears that there are
synergistic effects causing death in wild rats which ingest the 3-chloro-l,
2-propanediol mixture, thus causing wide differences in the LD-5O doses.
Animals which eat relatively small doses of the material such as those in
Experiment I, but eat very little food to act as a buffer substance in
the intestinal tract, die with much greater rapidity and from smaller
total ingested doses, than do those which eat large quantities of food
along with the chemosterilant. These data are supported by the results
of Experiment VI, in which animals which were given no food died much
more rapidly than those which were given identical doses of the
chemosterilant but supplied with unlimited food as a buffer.

Support of the hypothesis is also supplied when a comparison is made
between the average lethal dose of rats which were given the
chemosterilant at a 0.5 per cent concentration in their food (416.9
mg/kg), and those which were given food containing 1.0 per cent U-5897 by

weight (321.7 mg/kg) .

38

39

ACCEPTIBILITY OF U-5897 TO RATS AS A FUNCTION OF DOSE CONCENTRATION

A comparison of results of Experiment III in which the rats were fed
a 0.5 per cent concentration of the chemosterilant, with the results of
Experiments I, IV, and V, in which the concentration was at a 1.0 per
cent level, seem to demonstrate that the alpha-chlorohydrin compound is
more acceptable to the animals if it is present in the lower
concentration. Apparently there is a noxious taste, odor, or some other
property which makes the chemical unpalatible to rats, but this property
is not as evident at lower concentrations in their food material. This
is again supported by the results of the previously'mentioned experiments,
since it was found that the average food consumption for rodents at the
1.0 per cent level in which no pheromone attractant was present, averaged
4.2 per cent of the normal rate for all animals in the group, while in
the group of animals which were given the 0.5 per cent concentration
without the pheromone added the average rate of food consumption for all

animals averaged 15.7 per cent of normal.

EFFECT OF USING THE PHEROMONE IN ESTROUS URINE AS AN ATTRACTANT

The primary question investigated appears to have been at least
partially answered by this research. The pheromone material which was
added to the chemosterilant was apparently effective as an attractant to
the bait. In tests involving single males with the chemosterilant
additive at both the 0.5 per cent and the 1.0 per cent levels, the
animals which were fed the chemosterilant with the pheromone present were
found to eat from.168.6 to 220.7 per cent more (see section on results
and discussion, Experiment IV), for both concentrations. The actual

numerical figures were 14.8 per cent of normal for the 0.5 per cent

40

concentration without the pheromone, as compared to 24.95 per cent of
normal for the 0.5 per cent concentration when the pheromone was present.
For the 1.0 per cent concentration, the figures were 2.9 per cent of
normal for no pheromone, and 6.4 per cent of normal with the pheromone
present.

Similar results were recorded when the mated.ma1es were compared in
the same manner. In this case, the average consumption for males at 1.0
per cent with pheromone present was calculated to be 7.8 per cent of
normal, or 229.4 per cent of the rate of consumption exhibited by the
males on the same food but without the pheromone, who ate only at the
rate of 3.4 per cent of normal.

This was also the case with the paired animals which were fed a 0.5
per cent concentration of the chemosterilant. Those males which were
attracted by the pheromone ate an average of 21.5 per cent of their
normal consumption, or 142.4 per cent as much as those males which had no
attractant. These animals ate only at a rate of 15.1 per cent of their
normal rate when given the chemosterilant material.

Female rats were also tested to determine the effect of the
pheromone as an attractant to the chemosterilant material. This group
showed the most drastic difference in consumption when the pheromone was
added, as opposed to the same dose without the pheromone additive. Here,
the test results show that females receiving no pheromone averaged 4.7
per cent of normal, while those receiving the pheromone attractant
averaged 37.9 per cent of normal, or 806.4 per cent of the rate in the

group without the attractant.

41

ATTRACTING.ABILITY OF THE PHEROMONE AT 0.5%.AS COMPARED T0 1.0% CONCENTRATION

A final comparison can be made to demonstrate that the ability of
the pheromone to attract rats is nearly equal at each level of the
chemosterilant additive. This ability was demonstrated ianxperiments
III and IV. The addition of a pheromone to the 1.0 per cent mixture of
chemosterilant reduces the average drop in food consumption to about 7.4
per cent of normal as compared to less than 0.1 per cent of normal if
urine is not added to the chemosterilant mixture at that concentration.
The reduction in food consumption at the 0.5 per cent concentration was
held at an average of 23.4 per cent of normal by the addition of the
urine in comparison to a drOp to less than 2.0 per cent of normal fer the
first two days when the urine was not added at that concentration of
chemosterilant.

If compared on the basis of how'mMCh more readily the animals are
attracted to the pheromone than to the plain food at each level, however,
those animals which are given estrous urine at the 1.0 per cent level
average 225.0 per cent greater food consumption than do rats given the
same food material but without the addition of the urine. Animals given
the urine attractant in a 0.5 per cent mixture of the U-5897 demonstrated
only 155.5 per cent greater ingestion of the material than their counter-
parts without the pheremone additive. The effectiveness of the
chemosterilant was apparently similar in both the 0.5 and 1.0 per cent
concentrations. This is demonstrated by the fact that 100 per cent of
all male rats tested at both levels developed bilateral lesions and

testicular atrophy.

LITERATURE CITED

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Beyer, G., 1965, Housing and Society, Macmillan Co., New Yerk.

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Bock, M. and H. Jackson, 1957, The action of triethylenemelamine on the
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44

Ericsson, R. J. and V. F. Baker, 1970, Male antifertility compounds:
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and N. D. Conner, 1969, Lesions of the rat epididymus and
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of post-testicular antifertility action of 3-chloro-l,2-propanediol.
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Harder, J. D. and T. J. Peterle, 1969, The application of an anti-
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Hayes,'W. J. and T. B. Gaines, 1959, Laboratory studies of five
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Howard, W. E., 1967, Biocontrol and chemosterilants. IN Pest Control:
Biological, ngsical, and Selected Chemical Methods. ‘W. W. Kilgore
and R. L. Doutt eds. 335L386, Academic Press, N. Y., 477 pp.

, 1965, Principles of vertebrate animal control. Cong. De
La ProteCtion des Cultures TrOpicales, 627-629.

_and R. E. Marsh, 1969, Mestranol as a reproductive inhibitor
in rats and voles. J. Wildl. Mgt., 33(2): 403-408.

 

Huffaker, C. B., 1958, Experimental studies on predation: dispersion
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Jackson, H., 1959, Antifertility substances. Phar. Reviews, 11: 135-172.

Jackson, W. B., 1951, Food habits of Baltimore Md. cats in relation to
rat populations. J. Mammalogy, 32(4): 458-461.

45

Kennelly, J. J., M; V. Garrison, and B. E. Johns, 1970, The effect of
U-5897 on the reproduction of wild rats. J. Wildl. Mgt., 34(3):

508-513 .

King, 0. ML, 1950, An ecological study of the Norway rat and the house
mouse in a city block in Lawrence, Kansas. Trans. Kan. Acad. of
Sci., Dec., 1950, 500-528.

Knipling, E. F., 1960, The eradication of the screw worm fly. Sci.
American, 203: 54-61.

, 1959, Sterile-male method of population control. Science,
130: 902-904.

, 1955, Possibilities of insect control or eradication
through the use of sexually sterile males. J. Econ. Ent., 48: 459-
462.

Linhart, S. B., H. H. Brusman, and D. Balser, 1968, Field evaluation of
an antifertility agent, stilbestrol, fer inhibiting coyote
reproduction. Trans. 33rd N. A. Wildlife and Nat. Res. Conf.

and R. K. Enders, 1964, Some effects of diethylstilbestrol
in reproduction in captive red foxes. J. Wildl. Mgt., 28: 358-363.

 

Littig, K. S., Bjornson, H. D. Pratt, and C. F. Fehn, 1969, Urban rat
surveys, U.S.H.E.W. Pub., 14 pp.

Lund, M., 1964, Resistance to warfarin in the common rat. Nature, 203:
778-

Marsh, R. E., 1968, Rodents as reservoirs of disease. Proc. Asia-Pacific
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and W. E. Howard, 1970, Chemosterilants as an approach to
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, 1969, Evaluation of meatranol as a
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Mgt- 9 333 133-138-

Marx, 1951, Experimental analysis of the hoarding habit in the rat. J.
Comp. Phys., 44: 168.

Michael, R. P. and E. B. Keverne, 1968, Pheromones in the communication
of sexual status in primates. Nature, 218: 746-749.

Orgain, H. and ML'W. Schein, 1953, A preliminary analysis of the physical
environment of the Norway'rat. Ecology, 34(3): 467-473.

46

Overman, R. S., M. A. Stahmann, C. F. Huebner, W. R. Sullivan, L. Spero,
D. G. Doherty, M. Ikawa, T. H. Graf, S. Roseman, and K. P. Link,
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Roelofs, W. L. and A. Coneau, 1970, Lepidopterous sex attractant
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Schein, M. W. and H. Orgain, 1953, A preliminary analysis of garbage as
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47
Wynne-Edwards, V. C., 1964, Population control in animals. Sci. American,

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Boston. 228 pp.

APPENDIX

APPENDIX A

A METHOD FOR CONTROLLING COMMENSAL NORWAY RATS
IN URBAN HABITATS

Contemporary efforts toward rodent control are often undertaken by
individuals or even groups, who are not thoroughly familiar with the
biological nature of the animals which they are attempting to regulate.
It should be axiomatic, however, that a thorough knowledge of the target
species be within the grasp of its human predator befbre he attempts to
undertake any type of control effort. Logically, then, the opening
sections of this appendix on rodent control should contain a discussion
of the basic biology of the Norway rat.

A significant amount of research was done during the 1940's and
1950's concerning the pepulation structure of wild populations of brown
or Norway rats. Although most of this work was done on the East Coast in
the Baltimore area, the data can probably be superimposed on the Michigan

area without a great deal of error being introduced.

BREEDING AGE AND POTENTIAL OF NORWAY RATS:

According to Calhoun (1962a), male brown rats are ready to breed at
the age of about 70-80 days, while females mature slightly'more slowly
(80+ days). After breeding, these rats have a gestation period of about
21-25 days (Silver, 1941). Female rats have an estrous cycle of about
4-5 days, so at the end of this period after parturition, they are ready
for another mating and subsequent pregnancy.

Davis and Hall (1949) have shown that male brown rats are able to
breed all months of the year, but that females, for the most part, have

certain peak months for reproduction (Davis and Hall, 1951). Large adult

48

49

females seem to breed during all months of the year with equal
probability, but smaller females have a bimodal breeding season with

peaks in spring and summer (Davis and Hall, 1951).

MORTALITY

The average life span for wild Norway rats is about 7.1 months
according to Davis (1948). He has stated, however, that there is a great
deal of variability in survival of'young dependent upon the time of
parturition. There also seems to be differential survival rates between
male and female rats, with the females seeming to live somewhat longer on
the average. Mortality may be attributed to several different sources.
Intraspecific competition is usually a significant factor because of
territoriality and stress (Calhoun, 1962a). Other factors are predation
by dogs, cats, owls, and man (Davis, 1948). Nutritional foOd require-
‘ments are frequently not met according to Davis and'Winsor (1948), thus

adding another increment to mortality.

CENSUSING

Emlen, Stokes, and Davis (1949) determined that by using bait
stations, numerical censuses of urban rat infestations could be taken
with 80 per cent accuracy. This figure was found to be highly preferable
in terms of accuracy over that used by Davis (1948) in farm populations.
His method was simply a modification of the Lincoln Index method, and
subsequent studies (Calhoun, 1962a; Emlen, Stokes, and Davis, 1949)
demonstrated that this was not accurate due to trap shyness and trap
proneness on the part of once-trapped individuals.

A method of direct enumeration of the animals has been used by

Calhoun (1962a). This method, which involves the capture of each

50

individual in the population, is obviously'highly impractical for field
work with wild populations of rats.

The only other type of census method available at the current time,
is that of a relative index which is determined by the presence of
visible rat signs such as rub marks, feces, gnawings, etc. (Littig gt_§1,,
1969). This method is used almost exclusively in nearly all rat control

programs where censusing is attempted at all.

CURRENT MICHIGAN RODENT CONTROL PROGRAMS:

Rodent control operations of cities in southern Michigan vary a
great deal in their mpgu§|opgrandi. The following is a description of
the techniques used in the Michigan cities of Muskegon, East Lansing,
Highland Park, and Lansing. These methods supply'a cross section of the
rat control programs used in Michigan. UnfOrtunately, only two or three
cities in the state besides Lansing and Highland Park have programs which
are on a similar scale of efficiency as these. The remaining
metropolitan areas follow procedures similar to those of Muskegon and
East Lansing.

Muskegon:

According to Jack Mason, the Chief of Environmental Health in
Muskegon Co., the city of Muskegon has a relatively inefficient control
program. The procedure is simply to mix up warfarin bait blocks
(specified concentrations of warfarin mixed with corn and other materials,
and encased within a parafin block for protection from the elements) and
distribute them according to complaints about rat problems from the
public. These baits are not checked on a daily basis due to lack of
funding for hiring personnel. Instead, they are inspected only at

infrequent intervals, and may or may not be replaced when they have been

51

completely consumed. No regular census is taken, and no attempt has been
made at censusing the populations either before or after control efforts
have been instituted.

East Lansing:

In East Lansing the control program, according to Donald Jenks who
is head of the East Lansing Department of Sanitation, is approached in a
manner which is somewhat more thorough than that in.Muskegon. In
addition to the complaint-reaction baiting program, there is a procedure
instituted in this area which consists of assigning one man to inspect
man-holes on a weekly basis, and dropping a warfarin mixture sealed in
plastic bags into any holes which show evidence of rat infestations.
This evidence is determined by the presence of feces, tracks, rub marks,
etc. Frequently, if a man-hole does not contain running water, one or
two bags of the warfarin mixture are drOpped into it "just to be safe".
Again no census attempts are made either before, during, or after control
efforts.

Highland Park

Highland Park has one of the best approaches in the state to the
problem.of rat control. Here the procedure follows several steps which
are under the direction of Deputy Health Officer Anthony P. Miano.

1) A team of sanitarians surveys a neighborhood to determine the
rat infestation using the standard census procedure described by Littig
gingl. (1969). At the same time, they evaluate the amount of harborage
and food material available to rats in the area.

2) At the completion of this step, the sanitarians then instruct
the property owners and tenants in the neighborhood to clean up the

property in terms of food and harborage which may support rats. The

52

penalty for non-compliance is the issuing of a citation and finally the
levying of a fine.

3) After the area has been cleaned up, poisoning teams enter and
distribute poison baits in a three-phase cyclic rotation. A sequence of
red squill, diphacinon, and fumarin baits are used for this purpose. The
teams simultaneously apply cyanogas powder to burrows and zinc phosphide
in sewers where severe infestations are evident. The major problem.1ies
in the fact that this program.on1y takes place during the summer months
when populations are at their peak density.

4) Additional inspection is made periodically by the sanitarians to
see that there is no recurrence of harborage and food material in the area
after the cessation of baiting.

Lansing:

The rodent control program in Lansing directed by John Ruskin and
R. H. Goodsell is at least as good as, and possibly better than, any in
the state, at least in the case of major neighborhood infestations.
General complaints are simply handled on an individual basis in which a
sanitarian or a rat control technician treats the area of the complaint
with diphacinon-block poisons which are commercially prepared. The
poison applied in this manner may or may not be rechecked on a regular
basis.

Major infestations of entire one block or larger areas are treated
on a large scale basis. Here each area is censused in the normal manner
(Littig gtual., 1969) and then the major locations of rat problems are
mapped. Some ”emergency baiting" is performed to reduce extremely severe
infestations of rats at this time, thus reducing migration to human

dwellings during the following step of the program.

53

Next, a full scale cleanup and ratproofing program under the
supervision of the county health department and the city vector control
department is initiated by the area residents.

The third step in the program is the placement of poison baits such
as commercially prepared diphacinone. This bait is then checked on a
regular basis by either the residents or the health department employees,
and is replaced as necessary.

After a set period of 2-3 weeks, the poison material is removed to
minimize the possibility of selection for genetic immunity. At this time,
another census is made to determine the overall effect of the treatment
program, If success was generally achieved, any remaining isolated
infestations are treated on an individual basis with cyanogas and
diphacinone. If the entire program is found to have had suboptimal
results, full scale rebaiting is repeated throughout the entire target
area.

The single most outstanding feature of the procedure lies in its
year-round application. This factor makes it much more effective than a
simple summer program, since it is possible to attack the rat population
during the winter months, when they are at their lowest numerical
densities.

A major fault, however, is that the program.is not a regular or
continuous event. It is, at best, a sporadic effort, relying on public

pressure and allocations of funds for its institution.

SUGGESTIONS FOR AN ALTERNATIVE APPROACH TO.A CONTROL PROGRAM
The literature clearly shows that any'functional control program
must be a multifaceted approach in which poisoning is only a supplement

to environmental clean-up. The application of a chemosterilant material

54

rather than a purely toxic material may be a method of the future which
will create a more desirable final end point; however, materials of this
type are not yet available for widespread use, and therefore cannot be
considered at the present time. The same status applies to the
utilization of pheromone attractant materials such as those discussed
previously in this paper.

The following is an outline of what I feel should be a theoretically
sound and practical approach to urban rat control using only'the
currently available materials.

A. Pre-Treatment Survey

The proposed control area must be surveyed to determine the
approximate extent of the rodent infestation. This should be done only
by personnel trained in the techniques of'making the survey and what to
look for during the actual operation. Such a training program should last
from two to three days, and should involve instructional pamphlets and
films as well as classroom lecture.

The survey itself should be carried out by groups of five persons,
one of which is a foreman who is responsible for transportation and for
coordination of activities. The other four should work in pairs and
survey one-block areas from both sidewalks and alleys. They should note
signs of rat infestations, as well as units of harborage and food. Such
information should then be recorded on standard check-off forms such as
those used by the U.S. Public Health Service.

Sewer infestations which will be discussed 1ater,:must be determined
in a similar but separate operation in which the survey team looks in man-
holes for rub marks and droppings, and along streetside curbs for

burrows.

55

B. Analysis of Survey Results

The findings of the survey teams should be analyzed subsequent to
the completion of the Operation, and the location of infestations should
be marked on a transparent overlay'map of the urban area. The greatest
concentrations of rodents, are then assigned the first priority, with the
other areas being treated with as much emphasis as the monetary budget
will allow.

C. Application of Poison
Surface Areas

After the target treatment areas have been assigned, a poisoning
program.can be initiated. This must be accomplished before cleanup
operations in order to prevent dispersion of the rodents. Since anti-
coagulant poisons of both coumarin and indandione derivatives have been
demonstrated to be the safest and most effective when properly placed
(Hayes and Gaines, 1959; Bjornson, Pratt, and Littig, 1968), these
toxicants should be used exclusively in surface locations. Single dose
poisons such as 1080 and 1081 are probably'more effective baits for use
in sewers for the most part (Bjornson, Pratt, and Littig, 1968).

A useful precaution in applying poison baits to an area is to use a
system of rotation of toxic substances. This would effectively reduce
any possibility of the rodents developing a tolerance to a specific
poison as has been demonstrated in Great Britian (Lund, 1964).

.A system should be used in which diphacinone or pival, which are
indandione derivatives, are applied fer a three week period, all
remaining poison should be removed. This will maximize the deleterious
effect on the rodent population, since nearly all rodents would have an

opportunity to ingest the bait within this period. It will also minimize

56

the hazard to non-target animals, including children, since there will be
no unconsumed bait remaining and available to them. As a further pra-
caution, the occupants of all residences treated.with poison should be
informed of the project and poison by a form letter delivered at the time
of bait placement.

At the close of this initial poisoning program, an environmental
clean-up should be initiated as described below in part D. This should
be immediately followed by the re-introduction of poison for another
three-weak period. This second poisoning program.shou1d employ warfarin
or a similar hydroxycoumarin base anticoagulant, thus rotating toxic
materials as previously suggested. Following this application, a two to
three month waiting period should be observed, after which another poison
application can be made if deemed necessary.

Sewers

Sewers can be treated simply by placing large quantities of single
dose poisons in manholes where rats are in evidence. Since these areas
are effectively removed from.both pets and children, highly toxic
compounds such as sodium.flouracetata (1080) and flouroacetimdde (1081)
are recommended for use here. These poisons usually require fewer man-
hours for supervision and a smaller quantity of bait since after the
initial bait placement in all manholes which show signs of rodents, the
bait need be checked only at monthly intervals. Because sewer populations
of rodents are not frequently in direct contact with humans, and therefore
not as serious a problem, some bait shyness can be tolerated if the
financial cost is minimized.

D. Environmental Clean-up and Ratproofing
Upon completion of the initial poisoning program, an official should

contact property owners and tenants in the target area and instruct them

57

to have all harborage removed or made rodent proof within a given period.
They should also be required to use rodent proof garbage storage or
disposal facilities and be informed of the immense value of these
measures. It must be made clear to area residents that the poisoning
program is not permanently affective without the subsequent destruction
of all rodent harborage and food sources. It should also be clearly
stated that future attempts at poisoning, or a continuation of the
program, will not be made until the cleanup operation is completed. In
extreme cases of non-compliance, legal action may be necessary, but
should be used only as a last resort.

E. Expected Results of the Program

After the survey has been completed, an efficient overlay map. of
rodent concentrations in the area will be available for reference. This
will provide the information necessary to maximize all control efforts in
areas where they will be most effective and beneficial.

The application of poisons as outlined above, should reduce the
rodent population by up to 100 per cent, depending on the efficiency of
bait placement. An average result with proper placement and renewal of
bait should approach 90 to 95 per cent mortality in any given area.
According to Emlen gt a_1_. (1948), if a loss of these dimensions is
incurred in a wild population of Norway rats, the rate of recovery is
reduced to about 1 to 3 per cent per month. It should be noted that if
the poisoning campaign occurs just before the winter, the rate of
recovery will probably be even slower, since Davis (1950) found evidence
of depressed reproduction rates from November to April.

The most lasting effect will be caused by the removal of harborage

and garbage from the environment. Orgain and Schein (1953) demonstrated

58

that removal of either will cause drastic reduction of up to 50 per cent
of the rodents without any additional control method being used.
Elimination of both harborage and food sources such as garbage will
effectively extirpate the population within a six-month period.

‘When this method of habitat manipulation is combined with an
extensive poisoning program, the result should reduce populations to zero

and it should remain at that level as long as sanitary measures prevail.

 

APPENDIX B

It was stated earlier in this paper that Norway rats can be
regarded as a semi-parasite of human populations. The graphic model
below (see Figure 9) is an attempt to describe the basic function or
niche filled by rats in an urban environment or ecosystem. It must be
realized that the human influences in this model can be expanded'gg
infinitum.and probably are. This model, therefore, does not attempt to
include all of these factors, g,g, industrial labor unions, political
systems, social pressures, profitaering, atc., both for the sake of
clarity and in the interests of time and space.

In defense of my statement describing these introduced rats as being
semi-parasitic, it must be admitted that such entities as "feral"
populations of rats exist in local areas far removed from human housing,
but even these often depend upon the technology of man to provide them
with their daily food through the medium of cultivated crops. It is
within an urban ecosystem that rats truly become inextricably'intertwined
with human populations. They may function in a somewhat beneficial manner
for human populations through their garbage removal actions. This
example might cause them to be considered as somewhat commensal rather
than truly parasitic. They might take on the title of competitor in
another instance, when they consume goods which might otherwise be
consumed by humans. The fact remains that they still depend upon man for
a majority of their life supporting requirements. For this reason, I
choose to label them as semi-parasites.

Rodent populations, similar to most other living organisms, must be

supplied with three resources, each of which is a density dependent

59

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limiting factor. These factors are the most evident components of K, or
the carrying capacity of the environment referred to by Smith (1952).

The components under consideration are simply food, water, and harborage
(Bjornson gt.§13, 1956). Actually in a natural situation, water may be
the least critical of the three limiting factors, and is only very
infrequently of significant importance to the survival of the rodent
populations. The model below graphically'demonstrates the normal path-
ways through which these resources ara acquired by the rodents. Its
legend can be stated quite simply. The boxes are the significant factors
which figure in the survival of rat populations in an urban ecosystem.
The broken lines represent a man-directed, desirable relationship between
the factors represented by the boxes, whereas the solid lines are

representative of undesirable relationships from the viewpoint of human

populations.

Part I: THE SUBURBS

By definition, a model of an ecosystem is complicated by interactions
between each of the components. Perhaps the most appropriate place to
begin a description of this model is in the left hand margin at the box
labeled Middle and Upper Income Human Concentrations. This component of
an urban ecosystem (probably this should be classified as the residential
section at the outer fringe if an urban area, or the suburbs) exerts its
effects upon rat populations in each of three major catagories, all of
which are tied together in a common gathering facility--the sewer system.
In order to understand these effects, certain inherent characteristics of
an urban or suburban environment must be recognized.

First, the adversity caused by standing water from rain storms in

any urban ecosystem must be considered. Large puddles in streets

62

virtually bring traffic to a halt. Similar puddles on private peoperty
destroy expensive lawns or block sidewalks, residual stagnant water forms
a breeding place for mosquitos, etc. All this creates a valid need for
rapid drainage of property. This, of course, is accomplished through the
medium of underground sewer systems in the majority of urban areas.

Secondly, the eating habits of most families at the middla‘to high
income level described here must be considered. Normally, families within
this economic bracket tend to select food which affords a minimal amount
of waste, g,g, canned or boneless ham, relatively fat free meats (primarily
beef), a large quantity of boxed or dehydrated foods, especially potatoes
which do not require peeling, etc. (U.S.D.A. Report, 1956: 106-108, 190).

The relative abundance of garbage disposals in this economic class
then becomes a factor. What waste remains from human food is rapidly
ground into rather fine particulate matter and flushed into the city's
sewer systems, often the same system as the excess run-off from the rain
storms, since in many cases storm sewers and domestic sewers are not
effectively segregated.

The third major consideration in the discussion of these middle and
upper income families (which is also an obvious component of any economic
class) is that of the biological human wastes or excrements which are also
flushed into the sewer systems. In this case there is the additional
factor of an enormous quantity of bacterial flora which is attached to
and included within these excrements. Society has correctly placed
premium importance upon flushing these bacteria away in an attempt to
reduce the possibility of recycling within large human populations, thus

creating the hazardous possibility of epidemiological disease.

63

In looking at these sewer systems, however, it becomes evident that
for all of their beneficial function, they have a tremendous potential
for causing highly detrimental effects to human populations. Due to
their basic nature of construction, they form ideal harborage for rats.
They are dark and offer a minimal amount of physical disturbance. They
are of nearly constant warm temperature and are at nearly constant
humidity. In addition to this harborage, the sewers, through design of
purpose, afford an ample quantity of water for rodent populations, thus
supplying two of the three basic requirements or limiting factors for
rats. Now, if the contributions made by garbage disposals are added, a
total set of necessary requirements are present. All of the ingredients
have coalesced to support a subterranean rat population in the sewer
systems of a city. But not only do these rodents have the benefits of
food, water, and harborage from these sewers, they are also exposed to
and live in the bacterial flora which human populations once attempted to
dispose of by flushing down sewers.

Now comes the simple biology of the animal. Similar to mites on
oranges (Huffaker, 1958), house mice (Southwich, 1955; Southern and
Laurie, 1946) and muskrats (Errington, 1939), the rats expand in numbers
until the food supply is depleted and intraspecific competition for this
resource becomes a significant factor. Perhaps in a rainy season when
sewers become flooded, competition for space becomes the governing agent.
In either case, the animals begin to move out of the sewers and appear at
ground level where, carrying large bacterial infestations, they must
immediately begin searching to supply their three basic limiting factors

or components of K.

 

64

Part II: THE INNER CITY

In order to facilitate the most meaningful description of this
model, it becomes expedient to interrupt the apparent continuity of flow
at this point, and address the reader to the extreme right hand margin,
or the box labeled Low Income Human Concentrations. This area can
probably be classified as the inner city, or the underprivileged urban
residential area.

It must immediately be stated that this segment of the population
has sewage facilities and systems probably much older but almost similar
to those of the previously described economic segment. ‘With the major
exception of more garbage disposals in the latter segment, the systems
are equal. The fact that these low income dwellings and residences are
interconnected by the sewer systems with those of the higher income
levels is significant however, as will become more apparent later in this
discussion.

Normally, an urban human population which exists at an income level
such as that described here, is made up of blue collar workers. This is
demonstrated in the model by the broken arrow which represents a
beneficial relationship between the urban population and the industrial
plants, 2,2, the availability of employment. The solid arrow from the
industrial plants to the urban populations symbolically demonstrates that
these workers are paid lower wages in comparison to those paid to
residents of the suburbs, thus leading to the defined low income level.
(It must be recognized that other occupations with low wages also exist
in an urban ecosystem, but the factories are the best example for

demonstrational purposes in this case.)

65

Inhabitants of these low income urban areas are the providers for
and the victims of at least three more or less separate sources of rat
infestations. Perhaps the most simple of the three are the rat
infestations existing within the industrial plants which are quite
frequently located very near, or adjacent to, low income housing. These
plants are by nature large and impersonal structures which afford a
maximum.number of hiding places or harborage for rodent populations.
They also supply a ready source of water from condensation of pipes,
dripping faucets, wash rooms, etc. When any of the employees discard
part of their lunch (multiplied by several hundred workers in the plant)
there is a ready supply of food fer the endemic rodent population. If
this food is supplemented by any of innumerable sources in the general
area of the plant, 23g, garbage cans, dog food, production of edible
materials in the plant itself, etc., the rodent population is able to
maintain itself, often in spite of poisoning Operations or other control
efforts within the factories.

The second source of rat infestations in low income areas is often
brought about as a direct result of the low income of the inhabitants.
Since the economic level is low by definition, frequently there is not
enough money to purchase food of the quality consumed in higher income
homes (U.S.D.A. Report No. l, 1956). These lower quality and frequently
deficient diets often include relatively high waste foods such as fatty
roasts and cuts, or slabs or ribs. Other common high waste items are
starchy foods such as fresh potatoes and sweet potatoes, or rather bony
items such as chicken. All of these foods have a higher incidence of
occurrence in homes with an income level of $5,999 and below, than in

homes with a higher annual income level (U.S.D.A. Report No. 1, 1956:

66

66-76, 106-108, 190). Since a large portion of this food is not usable
or used, 3.3. fat and suet on meat, chicken bones, potato peelings, etc.,
it is normally discarded as garbage. This garbage may often be stored in
paper bags or cardboard boxes since families may not be financially able
to purchase proper garbage containers. These bags or boxes might then be
stored in basements or back yards until such time as is convenient for
removal to a suitable dump or other garbage disposal facility (Orgain and
Schein, 1953). The time period involved here could conceivably be rather
lengthy simply due to the financial burden of paying to dump the waste
products, or to possibly paying to have either a professional or a friend
with an automobile remove it. Such a removal system is obviously highly
inefficient, and contributes tremendously to the availability of food for
rat populations.

In assition, there is the third problem of the cheap, rented housing
in which low income families frequently live. These dwellings are often
'well past their prime and are rapidly decaying or becoming dilapidated
due to overuse, abuse, and lack of normal maintenance (Schorr, undated).
These neglected structures not only permit nearly'unobstructed entry for
rats, thus giving them access to garbage and trash stored in cellars, but
such dwellings also afford a nearly unlimited quantity of harborage for
the high density of rodents the supply of food present.

The harborage provided by the deteriorated.buildings in these areas
is often supplemented by accumulations of abandoned appliances,
automobiles, rubble, lumber, etc., between buildings. Consequently,
rodents have very little difficulty in finding all of the requirements

for survival.

67

Now it becomes feasible to return to those rats which have moved out
of the sewer systems due to intraspecific competition. As they emerge
from the sewers and begin to disperse, they are faced with the problem of
finding harborage, food, and water. If they move into the suburbs, they
are often attracted and supported by dog pans in which food pans are set
out in the evening, and scraps of dog food remain for the rats to devour
before the dish is taken away just prior to feeding time on the following
day. In some cases, these moving rats may encounter uncovered garbage
cans, and occasionally, they may find fruit from back yard apple trees.
In no case is food impossible to locate if sufficient effort is exerted.
Harborage, too, is quite accessible. Since Norway rats are normally
burrowing animals, they are quite accustomed to digging holes under the
foundations of buildings or along alleys. 'Water, as stated previously,
is almost never of consequence.

A comparison of the availability of food, water, and harborage in
suburban middle income residential areas with their availability in the
inner city "ghettos" generally shows a greater quantity of these factors
present in the latter areas. These environmental conditions probably
provide a much higher carrying capacity for rodents in the inner city
residential areas than environmental conditions prevalent in middle
income suburban residential areas. Studies by Davis on city vs farm rats
(1949) and by the Douglass Commission and published in transcripts of the
Commission hearings (1967) on housing problems and the Commission report

(1968) also seem.to indicate that this may be the case.

 

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