BIOLOGY AND CONTROL OF INSECT
AND RELATED PESTS OF SHEEP
John E. Lloyd, Professor of Entomology
Rabinder Kumar, Research Associate
Everett W. Spackman, Extension Entomologist
University of Wyoming
Laramie, Wyoming
This material was prepared under Inter-Agency Agreement EPA-78-D-f-0473
between the University of Wyoming and EPA Region VIII Denver.

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Table of Contents
Introduction 		1
Insecticide Use		1
Precautions 		1
Insecticide Formulations 		2
Preparation of Correct Insecticide Concentration 		2
Dilution Table 		2
Formulas 		2
Methods of Insecticide Application 		A
Dip Vat		A
Dilute Spray 		5
Pour-on 		5
Dust		5
Spot Treatments		7
Residual Wall Spray 		7
Space Sprays or Aerosols		7
The Pests and Their Control 		7
Biting and Nuisance Flies 		7
Black Flies		7
Biting Midge 		10
Mosquitoes		10
Horse Flies and Deer Flies		12
Stable Fly		12
Horn Fly		13
House Fly		14
Control of Flies		15
Sheep Bot Fly		15
Wool Maggots		16
Sheep Ked		17
Ticks		18
Sheep Lice		19
Mange Mites		21
Sarcoptic Mange 		21
Psoroptic Mange 		21
Chorioptic Mange 		22
Control of Mange Mites 		22
ii

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BIOLOGY AND CONTROL OF TNSECT
AND RELATED PESTS OF SHEEP
by
John E. Lloyd, Professor of Entomology
Rabinder Kumar, Research Associate
Everett W. Spackman, Extenion Entomologist
University of Wyoming
Laramie, Wyoming
Introduction
Many insects and their relatives
are important pests of sheep. Not
only do these pests cause losses in
production, but several are vectors
of diseases.
By close observation of his
animals, the producer can identify
insect problems and select the
most appropriate control or preven-
tive measures for his own operation.
Insecticide Use
A sound sheep management program
includes prevention and control of
insect and related pests. Very often,
control of insect pests involves the
use of an insecticide. These chemicals
must be used in a manner to minimize
hazards to the animal, the applicator,
the consumer and the environment.
¦ The sheep producer must first
recognize the insect problem or
potential problem. He might be
faced with an insect infestation
that requires immediate attention,
or he may know from past experience
that it is time to treat in order
to prevent a problem.
Precautions
When it becomes necessary to use
an insecticide, the label of the
appropriate formulation should be
read and understood. Be sure that the
formulation is approved for the intended
use. Some insecticide formulations
are for crop use only and not for use
on animals. When not in use, all
insecticides should be placed in a
proper storage area that can be
locked securely.
Before using the insecticide,
thoroughly familiarize yourself with
safe handling procedures, symptoms
of poisonsing, if any, and what to do
in case of an accident.
Apply the insecticide in a manner
consistent with directions on the
label. If the compound is not ready-
to-use, then it must be diluted to
give the correct concentration. Pre-
pare only as much dilute material as
will be needed at one time.
Insecticide applications should be
made out-of-doors to provide sufficient
ventilation. Observe label precautions
regarding treatment of animals that for
reasons of health, age, condition, etc.,
1

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may be adversely affected by the
treatment. Also observe precautions
concerning use in conjunction with
other insecticides or with medica-
tions.
Observe the required time
interval between treatment and
slaughter of animals. The purpose
of this waiting period is to avoid
residue levels that may exceed
established tolerances.
Insecticide Formulations
Several different kinds of
insecticide formulations are avail-
able. Some, such as dusts or oil
solutions are ready-to-use, directly
from the original container, while
others, such as wettable powders
(WP) and emulsifiable concentrates
(EC) must be diluted prior to
application. Wettable powders are
dry concentrates that are formulated
with wetting agents so they will
disperse in water. Agitation of
the diluted material is necessary to
keep the insecticide in suspension.
Emulsifiable concentrate insecti-
cides also contain a high percentage
of active ingredient and must be
diluted prior to use.
The concentration of a wettable
powder is expressed as a percentage,
for example, 25% malathion wettable
powder. The concentration of an
emulsifiable concentrate may be
expressed as percent active ingre-
dient, or pounds of active ingredient
per gallon of concentrate. Fifty-
seven percent malathion emulsifiable
concentrate contains 5 lb. of mala-
thion per gallon.
The problem of determining the
quantity of wettable powder or
emulsifiable concentrate that will
be needed to prepare a certain volume
of dilute spray or dip liquid can be
solved rather easily with the help
of either a dilution table or a
formula as presented below.
Dilution Table
To prepare a spray or dip with
a desired percentage of active
ingredient, only the concentration of
the formulation need be known to
use the Dilution Table. The figures
presented in the table represent the
amount of pesticide formulation for
each 100 gallons.
For example:
Preparation of Correct Insecticide
Concentration
Preparation of the correct
concentration of insecticide is
essential for successful control.
Errors in determining the quantity
of the insecticide concentrate that
must be mixed with water or oil can
result in the use of excess toxicant
that is costly, and may lead to
toxicity or residue problems.
The concentration of insecticide
in wettable powders or emulsifiable
concentrates is expressed on the label.
A 0.125% concentration of coumaphos
(Co-Ral^ ), is recommended for sheep
ked control. To make a 0.125% spray
using a 25% wettable powder (WP),
the Table tells us to mix A lb. of
the wettable powder in 100 gallons of
water.
Formulas
Emulsifiable concentrates. - Two
different formulas may be used to
determine the amount of emulsifiable
concentrate needed to prepare a spray
or dip containing a given percentage
of active ingredient. In the first,
the concentration of emulsifiable
2

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DILUTION TABLE
Percentage of actual chemical wanted
Formulation	0.0313%	0.0625%	0.125%	0.25%	0.5%	1.0%






Wettable
Powder
(WP)






15% WP
1 2/3
lb
3
1/3
lb
6 2/3
lb
13
1/3 lb
26
2/3
lb
53
1/3
lb
25% WP
1
lb
2

lb
4
lb
8
lb
16

lb
32

lb
40% WP
5/8
lb
1
1/4
lb
2 1/2
lb
5
lb
10

lb
20

lb
50% WP
1/2
lb
1

lb
2
lb
4
lb
8

lb
16

lb
75% WP
1/3
lb

2/3
lb
1 1/3
lb
2
2/3 lb
5
1/3
lb
10
2/3
lb






Emuls ifiable
Concentrate (EC)






1 lb actual/gal















(10-12% EC)
2
Pt
4

Pt
1
gal
2
gal
4

gal
8

gal
1.5 lb actual/gal















(15-20% EC)
1 1/2
Pt
3

Pt
6
Pt
1
1/2 gal
3

gal
6

gal
2 lb actual/gal















(25% EC)
1
Pt
2

Pt
4
Pt
1
gal
2

gal
4

gal
3 lb actual/gal















(33-35% EC)
3/4
Pt
1
1/2
Pt
3
Pt
6
Pt
1
1/2
gal
3

gal
4 lb actual/gal















(40-50% EC)
1/2
Pt
1

Pt
2
Pt
4
Pt
1

gal
2

gal
5 lb actual/gal















(57% EC)
7/16
Pt

7/8
Pt
1 3/4
Pt
3
1/2 pt
7

Pt
1
3/4
gal
6 lb actual/gal















(60-65% EC)
3/8
Pt

3/4
Pt
1 1/2
Pt
3
Pt
6

Pt
1
1/2
gal
C lb actual/gal
1/4
Pt

1/2
Pt
1
Pt
2
Pt
4

Pt
1

gal
lb = pounds
pt = pints
gal = gallons

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concentrate is expressed as lb. of
active ingredient per gallon.
In the second, the concentration
is expressed as % active ingredi-
ent .
Wettable powders. - The following
formula is used to determine the lb.
of wettable powder needed to prepare
a spray or dip containing a given
percentage of active ingredient.
gal	% active
spray X ingredient X (8.3)
wan ted 	wanted	
lb. active
ingredient/gal X (100)
of concentrate
or,
% active ingredient in concentrate
% active ingredient wanted
number of parts of
finished spray or dip
that must contain 1
part of the concentrate
gal	% active
spray X ingredient X (8.3)
wanted	wanted 	
(% active ingredient in WP)
For example:
How many pounds of lindane 25%
wettable powder are needed to make
100 gallons of spray containing 0.03%
1indane?
(100) X (0.03) X (8.3) = 1 lb
25
Methods of Insecticide Application
For example:
How many gallons of 25% lindane
(2 lb./gal) emulsifiable concentrate
are needed to make 100 gallons of
spray containing 0.25% lindane?
Using 2 lb. active ingredient/gal
(100) X (0.25) X (8.3)
= 1 gal
(2) X (100)
or,
Using 25% active ingredient
25% = 100
0.25%	1
The dilution is one part 25%
lindane in 100 parts of finished spray
or dip. This would be equivalent to
1 gallon 25% lindane to 99 gallons
water.
Application techniques commonly
utilized in the control of several
different pests are discussed here.
More specific information is pre-
sented later along with the individual
pests. The purpose is to familiarize
the reader with common application
techniques and terminology.
Dip Vat
Dipping is a highly effective
method for controlling several para-
sites of sheep (Figure 1). Although
the initial cost of the vat plus
the insecticide Ls high, no method
provides more thorough coverage of
the animals.
Dip vats should be located in
areas where there is no problem of
contamination of ground water, streams
or ponds. They should also be pro-
vided with a drain pen so that excess
insecticide solution will drain back
into the vat.
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Vats must be thoroughly cleaned
and freshly charged prior to dipping.
Check with State Department of Agri-
culture or Health Department officials
for current procedures of disposal of
unwanted insecticide.
The vat should be charged immed-
iately prior to dipping. The volume
of the vat should be determined prior
to charging. This can be determined
by pouring water into the vat from a
measured drum or tank, by metering
the water into the vat, or if the
dimensions of the vat are known, by
calculating the volume. Both emulsi-
fiable concentrate and wettable powder
formulations should be suspended in
water in a premix tank before being
added to water in the vat.
If a vat is to be replenished during
dipping, it is advisable to situate a
tank or drum adjacent to the vat. It
shou] d empty directly into the vat.
This container can also be used in pre-
paration of the initial charge.
Thorough mixing of the insecti-
cide solution prior to dipping is
essential. Periodically, a device
should be dragged along the bottom
of the vat to suspend insecticide
that might have settled to the
bottom. If a wettable powder insec-
ticide is used, it should be mixed
with a small quantity of water and
converted to a slurry prior to addi-
tion to the vat.
300 to 350 lbs. per square inch is a
method that provides penetration into
the fleece (Figure 2). Of course, this
method requires fairly expensive equip-
ment. A fairly high volume of spray,
around 1 to 2 gallons, is required for
complete coverage of one mature animal.
For control of sheep keds, low
pressure sprayers or even sprinkler
cans (Figure 3) can be used to apply
about one quart of ]iquid insecticide
per animal. It is not necessary to
thoroughly soak the animals in order
to control keds in this manner. To
use the sprinkler can, crowd the
sheep in a small pen (out-of-doors) and
walk among them sprinkling the insecti-
cide over the heads, necks, tops and
sides.
Pour-On
The pour-on method used for ked
control on sheep involves topical
application of a few cc to a single
spot on the fleece (Figure 4). A
calibrated syringe is used to apply
tlie material since a very small volume
of liquid is involved. Several
insecticides are approved for use as
pour-ons for cattle, but be sure that
the material you are using is
approved for use on sheep.
Dust
Certain precautions must be
observed in dipping sheep. Sheep
are susceptible to chilling if dipped
during cool weather. They should be
dipped during the early part of the
day and given sufficient time to
dry before the sun goes down. Lambs
should be dipped separately to
reduce the danger of drowning.
Dilute Spray
Application of insecticide by
means of a high pressure spray, i.e.,
Dusting of sheep has been a popular
method of treating sheep for many years.
Sheep dusted in the spring of the year
do not become wet and are therefore not
subjected to chilling. Dusting is less
hazardous to the sheep than is dipping.
Dusting by hand is a suitable
method for small numbers of sheep
(Figure 5). The method is time-con-
suming because animals have to be
caught individually, then dust is
sifted onto the wool then rubbed in
lightly to work the dust down to the
skin.
5

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9
Figure 1. Dipping sheep.
Figure 2. Application of a high pressure spray to sheep.
Figure 3. Insecticide application by means of a low pressure
compressed air sprayer (3a) and sprinkler can (3b)
for control of sheep ked.
6

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Power dusting by means of a
sheep duster has been popular for
large range flocks (Figure 6). After
shearing, the sheep are crowded into
a chute. Then, the duster is
started and the sheep are driven
through the curtain of dust.
Spot Treatments
Various kinds of application
devices are available for spot
treatment of areas on an infested
animal. For example, insecticidal
smears and foams can be used to
prevent or treat a wool maggot
infestation in the fleece (Figure 7)
or a dust or spray or oil solution may
be applied into the ear canal for
control of the spinose ear tick
(Figure 8).
Residual Wall Spray
Wall sprays are applied at
low pressure, e.g. 80 p.s.i., to
produce a coarse spray. Various
kinds of sprayers, large or small
may be used. Spray should be
applied to resting places of flies,
for example, to fences and walls
(Figure 9) with care to avoid
spraying feed and water. Animals
should be removed from buildings
prior to spraying. One application
of an appropriate insecticide may
give fly control for several weeks.
Space Sprays or Aerosols
This is a method for quickly
clearing spaces of flying insects.
A machine is used that produces a
very fine mist or fog (Figure 10)
that remains suspended in the air
for several hours. Usually the
application is most effective
indoors and must be repeated daily,
The Pests
and Their Control
Numerous insect and related
pests attack sheep. In some areas of
the world, certain pests severely
limit sheep production. The following
are important pests of farm and range
flocks in some areas of the United
States.
Biting and Nuisance Flies
Flies are familiar to everyone.
Those that are particularly bothersome
to sheep are horn flies, stable flies,
horse flies, deer flies, mosquitoes,
black flies, biting midges, and house
flies. Flies severely affect the
performance of sheep. They hinder
grazing and cause sheep to bunch up
or lie down in order to be freed from
annoyance. They can remove considerable
blood, and many flies are important
in transmission of disease-causing
organisms.
Black Flies
There are many species in the
black fly family Simuliidae, and they
are among the smallest of the biting
flies. Frequently, they are called
buffalo gnats because of their "humped
back" appearance. Black fly may be
a misnomer because some species are
frequently tan or yellowish in color.
The four life stages of the black
fly are illustrated in Figure 11. The
duration of the life stages varies
considerably with the different
species. Several hundred eggs may be
deposited on or in the water by the
adult female. Larval and pupal black
flies spend their lives in rivers or
streams where fresh, running water
provides sufficient aeration. These
aquatic stages are attached to objects
such as stones, logs and submerged
vegetation. After emergence, the
adult flies are capable of moving
7

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Figure 4. A low volume pour-on application for control of
sheep ked.
Hand dusting of sheep.
Power dusting of sheep.
Spot treatment for control or prevention of a wool
maggot infestation.
Figure
5.
Figure
6.
Figure
7.
8

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Figure 8. Puff duster treatment of ear for control of ear
ticks.
Figure 9. Application of a residual wall spray.
Figure 10. A mist applicator (10a) and a fogger (10b).
9

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considerable distances from the waters
of their origin. Females are blood
suckers and may occur in large
swarms.
Biting Midge
The very tiny bloodsucking midge
or gnat, Culicoides variipennis, is a
common pest of sheep in the United States
(Figure 12). The females may attack
in large swarms, primarily in the
evening. These flies may be respon-
sible for sores and scabby areas on
the undersides of animals. In the
United States, C. variipennis is the
primary vector of bluetongue, a virus
disease of sheep and other ruminants.
larva
Figure 11. Life stages of a black
fly. The adult of this species is
approximately 3.5 mm.
Female black flies are attracted
in large swarms to the host animal.
They may fly about and get into the
nose, eyes, ears and mouth. They
feed either on exposed areas of
skin or deep within the hair coat.
They lacerate the skin and suck
oozing blood. Strong anticoagulants
in their saliva prevent coagulation
of the blood for some time after the
bite. A large, painful welt may
develop at the site of the bite.
Black flies can significantly
affect the performance of sheep, and
during severe outbreaks, death losses
have been reported.
Figure 12. The life stages of
Culicoides variipennis, a biting midge.
The adult is approximately 2 mm.
Ideal larval breeding sites for
C. variipennis usually consist of non-
vegetated, open areas of soft silty mud,
exposed to direct sunlight. Such
areas may be found in natural marshy
areas or along the margins of alkaline
bodies of water in the West. Very
dense populations of larvae can occur
as a result of pollution by livestock
or human wastes, e.g., near feedlots
or inadequate human sewage facilities.
Mosquitoes
Adult mosquitoes are small (body
length about 6 mm or less) delicate
organisms with a conspicuous long snout
10

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or proboscis. Mosquito life stages
are egg, larva, pupa and adult. The
eggs are laid on or near water. When
in contact with water the eggs hatch
and produce the aquatic immature
stages. The larvae or "wigglers",
with very few exceptions, are found
in standing water with relatively
little movement or wave action.
In the larval stage the mosquito
attains most of its growth. After
four larval stages of increasing
size, larvae molt to the pupal stage.
The pupa or "tumbler" moves about in
the water by a tumbling action.
After a few days, the pupa swims to
the surface of the water, and the
adult mosquito emerges from a slit
in the "back" of the pupa.
Usually, the adult male mosquitoes
emerge first and remain near the
larval habitat and fertilize females
shortly after their emergence. Most
fertilized female mosquitoes then
require a blood meal before egg-
laying.
Aedes. flood water mosquitoes are
extremely important pests because
there are many species, and they appear
in tremendous numbers. They are pro-
duced in vast inundated areas such as
marshes, flood plains, snow pools
and irrigated meadows. The adult
females are avid feeders on both man
and his animals. While most bites
occur during the early morning and
evening hours, some species will readily
feed during the daylight hours.
The life cycle of a typical Aedes
mosquito is presented in Figure 14.
The eggs of these species are laid in
moist soil in areas subject to
reflooding and where the females are
somewhat protected from the wind. The
eggs may survive for several years
before flooding. In temperate areas,
Aedes mosquitoes overwinter in the
egg stage, then hatch in the spring
due to spring runoff or irrigation.
Repeated flooding through the warm
months will produce additional broods
of some species.
Female mosquitoes of the genera
Aedes and Culex are serious pests.
Examples of the two genera are pre-
sented in Figure 13. Note that these
genera can be distinguished by the
shape of the tip of the abodmen.
Figure 13. Female mosquitoes of two
genera. The tip of the abdomen is
pointed in Aedes and blunt in Culex.
These specimens are approximately
5-6 mm long.
NV«-
;
Pupae or
Lorvoe or wigglers
Figure 14. The life cycle of Aed
es.
11

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The life history of Culex (Figure
15) differs from that of Aedes¦ The
eggs are deposited on the surface of
standing water in groups called
"rafts", and they hatch shortly there-
after. These mosquitoes are able
to utilize many different kinds of
standing water, fresh or polluted,
usually in open, sunlit locations.
Examples of suitable habitats are
ponds, ditches, puddles in corrals,
and artificial containers such as
poorly maintained stock tanks or
discarded drums, barrels and cans.
These mosquitoes overwinter in
sheltered locations as hibernating
adults.
r
j
Pl«M 0* lKTCtert

Figure 15. The life cycle of Culex¦
Horse Flies and Deer Flies
Cftrysp»
Oct fly
TobCM
Ho»« Ity
Totxrmi
ho»m "y
Figure 16. Adult deer fly and horse
flies. These specimens range in size
from 9 to 28 mm.
Adult horse flies and deer flies
usually appear in large numbers at
certain times during the season.
Females attack animals, and the bite,
which is extremely painful, causes
considerable flow of blood. Frequently
clusters of other kinds of flies will
surround pools of blood formed by the
feeding of horse flies.
The life stages of a horse fly
are presented in Figure 17. Usually,
the female files lay their eggs,
often attached to vegetation, near
the damp or wet soil of streams,
marshes, lakes or ponds. After a short
incubation period of approximately one
week, larvae hatch, then develop in
water or wet soil. Later in the
season, or possibly the following year,
full grown larvae migrate to drier soil.
Each forms a pupal case, from which an
adult fly will eventually emerge.
Horse flies and deer flies belong
to the same insect family, the
Tabanidae, and are similar in many
ways. Many species of horse flies
and deer flies attack livestock and
three are illustrated in Figure 16.
Deer flies are usually about the same
size or a little larger than the
ordinary house fly, and frequently
have distinct patterns on their wings.
Horse flies are larger and darker
than deer flies. Some are quite
large.
Stable Fly
The stable fly, Stomoxys calcitrans
looks much like a house fly except
that it has a prominent beak (Figure
18).
Eggs of the stable fly are deposi-
ted in wet and decaying organic matter.
Wet feed or hay contaminated with
manure, urine, and mud are particularly
good media for development of stable
12

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Figure 17. Life stages of a horse
fly-
Figure 18. The adult stable fly,
and enlarged, side-view of head and
piercing mouthparts. The specimen
is approximately 8 mm.
fly larvae or maggots. In areas
where bodies of water occur, stable
fly may be abundant because piles
of decaying "seaweed" are good
larvae media.
The life stages of the stable fly
are presented in Figure 19. After egg
hatching, the larvae pass through
three stages of increasing size.
After the larval stage a pupal or
inactive stage is formed. Eventually
an adult fly emerges from the pupal
case. Because of rapid development
from egg to adult, about 24 days,
stable fly can produce several
generations per season.
Adult
Mi
Eggs
Pupa
\
/
3rd Stage
Larvo
Figure 19. The life stages of the
stable fly.
Both male and female stable fly
readily attack animals. They have a
stout proboscis with which their
pierce the skin and suck blood. The
bite is painful.
Stable fly is a particularly
serious problem in areas where there
is considerable medium for production
of larvae. Such conditions frequently
exist in and around livestock buildings
and lots where stable fly can be found
in doors as well as out.
Horn Fly
The adult horn fly, Haematobia
lrritans, looks much liko a miniature
stable fly (Figure 20). Both sexes
13

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of the horn fly have beaks which they
utilize to obtain blood meals. The
horn fly is primarily a pest of cattle,
but is occasionally seen on sheep.
Ordinarily the flies congregate on
the shoulders and sides of the animal.
During extremely hot sunshiny or rainy
weather the flies may congregate on
the underside of the belly.
Figure 20. The horn fly.
is approximately 4 mm.
The adult
The adult female is usually found
on cattle and leaves only to deposit
eggs in fresh cattle droppings.
After hatching, the larval stages
develop rapidly in the cattle dung
pat. Pupation usually takes place in
the soil beneath the pat. Adults
emerge from pupae and seek out a
host. The cycle can take less than
two weeks in warm weather.
\

Eqgs
Pupo
*1TrTr^rT~7fn '\'
3rd Stage
Lorva
Figure 21. The life stages of the
house fly.
The four life stages of the
house fly, egg, larva, pupa and
adult are presented in Figure 22.
The complete life cycle from egg to
adult requires approximately two
weeks in warm weather.
House Fly
The house fly, Musca domestica,
is a widespread pest that is
familiar to everyone. Though it does
not inflict a painful bite because
of the nature of its mouthparts
(Figure 21) , it is a very annoying
insect and can torment sheep con-
siderably .
Figure 22. The adult house fly
and an enlarged side-view of the head
and sponging-type mouthparts. The
specimen is approximately 7 mm.
The house fly is a pest closely
associated with man's activities. It
is able to utilize many kinds of
organic matter, such as found in
garbage, as a larval medium. It is
14

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able to utilize all sorts of decaying
excrement. Primarily, it is
considered a pest in and around live-
stock buildings and feedlots.
Control of Flies
Several different insecticides
may be applied to sheep as a dilute
spray or dip for control of horn fly.
These treatments may also provide
some relief from attack by other fly
species.
Much can be done to alleviate
house fly and stable fly problems
around livestock buildings and
feedlots through sanitation and
proper management of manure. Basi-
cally this means either elimination
of larval habitat or modification in
such a way as to make it unsuitable
for fly production. Prompt and
regular removal and dispersal of
manure, soiled bedding and spilled
feed is a good fly preventive
measure, as is elimiation of wet
areas in pens and lots.
Insecticide-based control is
possible when a fly problem gets
out of hand around livestock housing
facilities. Residual sprays, applied
to walls, ceilings, fences and other
favored resting places are effective
and may last several weeks. For fly
control in buildings various insec-
ticide baits are effective against
house fly if used properly. For
fast but temporary control of
flying insects in confined areas,
fogs, aerosols or mist applications
are effective.
Out-of-doors, mist applications
that involve a finely divided spray
will disperse quite rapidly. The
dispersed droplets kill flies they
contact. This method, including
ground and aerial application, can
be used, however, for temporary relief
from a serious outbreak of flies.
Many populations of the biting
midge, Culicoides variipennis are
produced inadvertently on farms and
ranches, and may be eliminated through
management or cultural practices.
Examples of such larval breeding
sites are: sites where water-borne
human sewage flows out onto the
ground; puddles contaminated with
manure such as those that occur
near water tanks and in livestock
pens; and dirt stock ponds where
manure has been trampled into the
shallow water along the edge.
Mosquito annoyance may be reduced
through source elimination, i.e.,
elimination of water that provides a
suitable habitat for mosquito
larvae. Mosquito larvae can also be
eliminated through the removal of
protective emergent vegetation from
places such as drainage ditches and
the edges of ponds and lagoons.
In several locations, communities
as well as smaller groups of farmers
and ranchers have organized for mos-
quito control. Primarily these
programs have involved aerial appli-
cation of larvicides to vast areas of
flooded land.
Sheep Bot Fly
The sheep bot fly, Oestrus ovis
(Figure 23) is a common pest of sheep
and goats. The persistency of the adult
flies in depositing larvae in the
nostrils excites the animals and
interferes with handling and grazing.
The larval stages of the fly,
known as head grubs, live as parasites
within the nasal passages and frontal
sinuses. They may irritate membranes
lining the nasal cavities and predis-
pose the sheep to bacterial infection.
The resultant nasal discharge leads
to the term "snotty nose."
The life history of the sheep bot
fly is presented in Figure 24. During
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Figure 23. The sheep hot fly. The
adult fly is approximately 13 mm.
the warmer months of the year very
small, first-stage larvae are deposi-
ted in the nostrils by female flies.
These small larvae remain in the
nasal passages for a time, then
migrate to the frontal sinuses for
further development. After reach-
ing full growth in the sinuses,
larvae work their way out of the
nostrils and drop to the ground,
where they bury themselves and
pupate within a few hours. The
pupal period lasts about one month.
Currently, there is no practical,
approved method for control of this pest.
Wool Maggots
The larvae of many species of
blow fly have been reported to invade
wounds of livestock. Several species,
however, do not necessarily require
a wound in order to parasitize sheep.
The larvae of these flies are called
wool maggots or fleece worms.
The adult flies (Figure 25) are
often about the same size as the
house fly and dark bluish-green in
color with a metallic luster. The
larvae look like typical fly maggots.
Figure 24. Life cycle of the sheep
bot fly.
Figure 25. The life stages of a
typical blow fly or wool maggot. The
adult varies in size from 6 to 11 mm.
The factors surrounding strike or
egg-laying are not completely known,
however, several predisposing causes
have been reported. The primary cause
for strike is bacterial activity in
the wool, which can be stimulated by
contamination with urine, feces, sweat
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or an existing maggot infestation.
Maggots may live in the fleece, or
they may attack the skin and produce
lesions. The lesions and the maggots
irritate the animals. The sheep
become restless, stamp their feet,
constantly wag their tails, and bite
at the site of the trouble. They do
not feed properly, and become poor
in condition. Death may occur within
a few days.
Life histories of the several
species of wool maggots are similar
(Figure 26). The usual larval breed-
ing places are in carrion, but under
certain conditions they find a
favorable environment for development
on living sheep. Eggs hatch in a
few hours and maggots develop rapidly
completing growth in three to four
days. They then drop from the host
and enter the ground, where they
transform to the pupal stage. After
seven to ten days adult flies emerge
from pupal cases. Several genera-
tions develop each year.
Figure 26. The life cycle of a wool
maggot.
Much can be done to avoid maggot
infestation of animals through flock
management. Soiling of fleece should
be avoided, but if the breech area
becomes saturated witli urine and feces
during the blow fly season, wool
should be clipped from Che crutch
area. In order to avoid wounds that
may become maggot infested, sheep
should be handled gently and with
safe chutes and corrals. Lambing
and shearing early in spring prior
to the blow fly season is advisable.
Insecticides are used for pre-
vention as well as control. Preven-
tive dips or sprays may be applied if
animals scour during the warm months.
Wounds may also be treated. Infested
animals may be dipped or sprayed with
dilute insecticide. If only a few
animals become infested, spot treat-
ment of the infested site is a
possibility.
Sheep Ked
The sheep ked, Melophagus ovinus
is a common pest of sheep. It is a
wingless fly that has a tick-like
appearance (Figure 27). Two stages of
the insect may be seen on sheep, the
adult and the pupa. Both stages are
most commonly found on the underside
of the host, although they are not
restricted there.
Figure 27. The sheep ked. The adult
is about 7 mm .
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The sheep ked is a blood feeder,
and it crawls rapidly through the
fleece of the host animal. Damage
results from bites of the ked and
irritation to the sheep.
The entire life of a sheep ked is
spent in the fleece of the host
(Figure 28). Adult keds spread from
one host to the next by direct con-
tact. This is how keds transfer from
ewes to newborn lambs.
Figure 28.
ked.
Life cycle of the sheep
The sheep ked has an unusual means
of reproducing. The larval stage of
this fly develops within the adult
female. A single larva develops at
a time, requiring approximately eight
days. The adult female ked attaches
the fully developed larva to the
fleece, and the larva transforms into
the red, barrel-shaped puparium. A
new ked emerges from the pupa after
approximately 22 days.
Ked populations build up during
the autumn and winter months and
reach peak numbers in January and
February, then decline to lower
numbers that are carried over the
summer.
Several methods of control are
available for sheep ked. Each has
its advantages and disadvantages
depending on the particular sheep
management program. Most often,
sheep are successfully treated in the
spring after shearing. All sheep in a
flock must be treated, and all
animals introduced into a flock should
be treated in order to prevent
reinfestation. Methods of application
for sheep ked control include dipping,
high pressure spray, low pressure
spray (including sprinkler can),
pour-on, power dusting and hand dust-
ing.
Sheep Lice
Several species of lice can
infest sheep. These include one
species of chewing louse (the sheep
biting louse) and several species of
sucking lice. The sheep biting louse
and the sheep foot louse (a sucking
louse) will be discussed here.
The sheep biting louse, 'iovicola
ovis (Figure 29), is a small species
with a pale abdomen, darker thorax,
and reddish head. The sheep foot
louse, Linognathus pedalis (Figure 29),
is up to 2 mm long, has a short head,
nearly as wide as it is long, and
the abdomen is thickly covered with
long slender bristles.
The adult, nymphs, and egg stages
all appear on the host (Figure 30).
The three nymphal stages resemble
the adult lice in general appearance,
however they are smaller in size. The
eggs, which are quite small in size
are glued to wool fibers and hairs.
The sheep biting louse and sheep
foot louse demonstrate a pronounced
seasonal fluctuation in populations,
numbers being greatest in winter and
early spring, and lowest in summer.
Lice are spread by contact between
sheep. The sheep foot louse can also
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B
Figure 29. A, the sheep biting
louse (1.8 nun) and B, the sheep foot
louse (2.0 mm).
Figure 30. Life cycle of the sheep
biting louse.
be acquired from an infested
pasture.
The sheep biting louse is usually
most abundant on oJder sheep and
sheep in poor condition. Their
preferred location is near the skin
along the back and the upper sides.
In heavy infestations lice may be
found anywhere on the body.
Biting lice feed on the skin
scurf. They cause intense irritation
which sheep relieve by biting and
pulling the wool and by rubbing against
objects. The fleece of heavily
infested sheep becomes ragged and torn.
The sheep foot louse is a sucking
louse that feeds on blood. Usually
this louse is not considered very
injurious since feeding occurs on the
hairier parts of the sheep's body,
and the animal exhibits little dis-
comfort. In severe infestations,
however, it may cause some lameness.
Generally, lambs and younger sheep
are more heavily infested by the
sheep foot louse than are older animals.
Light infestations commonly occur as
small colonies of lice around the
accessory digits. From this location
they may spread down to the foot and
up the shank. In heavy infestations
they also infest the scrotum and
sometimes the belly of rams.
The sheep body louse, sheep foot
louse and other species that occur
on sheep may be controlled by the use
of an insecticide dip or high pressure
spray.
T icks
The Rocky Mountain wood tick,
Dermacentor andersoni and the spinose
ear tick, Otobius megnini can be
serious problems when they occur in
sheep producing regions. Rocky
Mountain wood ticks are important
pests of sheep for several reasons.
Considerable blood loss and severe
anemia can result from heavy infesta-
tions. These ticks may also cause
tick paralysis in sheep by the feed-
ing of females, and their injection
of a toxin into the blood stream of
the host. Finally, Rocky Mountain
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wood ticks transmit the pathogen of
tularemia to sheep.
By attaching deep in the ears,
the spinose ear tick causes consider-
able irritation and pain. The injury
predisposes the host to secondary
bacterial invasion of the inner ear.
The adult stage of the Rocky
Mountain wood tick (Figure 31) is
seen attached to sheep and other
large mammals in the spring. The
immature stages generally are not
seen because they parasitize small
mammals such as ground squirrels and
rabbits.
Figure 31. The Rocky Mountain wood
tick. The unengorged female is
about 5.0 mm.
The life cycle of the Rocky
Mountain wood tick is fairly complex
(Figure 32). In the spring adults
come out of hibernation and attach to
large mammals. Mating and feeding
occur on the host, then the females
drop to the ground in one to three
weeks. Egg-laying takes place on the
ground, and over 6,000 eggs can be
produced by one female. The larval
or seed ticks, which hatch in a month,
attach to small wild mammal hosts where
they feed for two to eight days, then
drop off. Nymphs, which appear three
weeks after the larvae drop, may
either hibernate that winter as nymphs
or find another small mammal host. If
another host is found, the nymph feeds,
drops off, molts, and spends the winter
as an unfed adult. Overwintering nymphs
seek small mammal hosts the following
summer, feed for about a week, then
drop off the host. After a quiescent
period, these nymphs molt and over-
winter as unfed adults.
Figure 32. Life cycle of the Rocky
Mountain wood tick.
The nymphs and larvae of the
spinose ear tick (Figure 33) are
the stages that are usually seen,
and these are found in the ear,
attached to the tender skin. Larval
spinose ear ticks hatch from eggs that
have been Laid on the ground. The
larvae climb onto the vegetation, feed
troughs, etc., to contact passing
host animals. After contacting the
host, the larval tick moves to the
ear where it attaches to the delicate
lining of the ear and engorges. It
molts in one to two weeks to the
first nymphal stage, then the second.
Nymphs may remain in the ear up to
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six months. The nvmphs then drop to
the ground, molt to the adult stage,
mate, and lay eggs.
Nymph
Figure 33. Life cycle of the spinose
ear tick. The engorged larva and
nymph, which occur in the ear, are
approximately 3.5 and 7.5 mm, res-
pectively.
examination is necessary for positive
identification of the type of mange
present because mites are barely
visible to the naked eye.
All of these mites have developmen-
tal stages similar to those of ticks,
i.e. eggs, larvae, nymphs, and adults
(Figure 34). All stages live only on
the host animal and are spread by
contact between animals or with
contaminated equipment.
Figure 34. The life stages of a mange
mit e.
Control of Rocky Mountain wood
tick is best accomplished by means of
an approved insecticide applied as a
high pressure spray or by a dip vat.
Spinose ear ticks may be controlled by
application of a dust or oil solution
directly into the ear.
Mange Mites
Several different mite species
produce a contagious disease of the
skin of domestic animals known as
mange. The type of mange is named
after the mite causing it, e.g. sar-
coptic mange, psoroptic mange, and
chorioptic mange which are caused by
Sarcoptes, Psoroptes, and Chorioptes
mites, respectively. For diagnosis,
mites are scraped from an infected
area of the host animal. Microscopic
Sarcoptic Mange
Sarcoptic mange is rare in sheep.
Adult sarcoptic mites (Figure 35),
burrow within the skin of the host
and cause severe irritation. Eggs are
laid within the burrows. Development
of'the mite from egg to reproductive
adult takes approximately two weeks.
This form of mange occurs only on the
nonwooly skin. Lesions usually first
appear on the head and face.
Psoroptic Mange
Psoroptic mange of sheep is also
called sheep scab. It is caused by
Psoroptes ovis (Figure 35). It is a
notifiable and quarantinable disease,
and when suspected should be reported
immediately to regulatory officials.
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Figure 35. Sarcoptes scabiei, a
mange mite. Microscopic in size.
Although it has not been reported
from the United States in recent
years, there is constant danger
of its reestablishment.
Figure 36. Psoroptes ovls, the
causative agent of sheep scab. Micro-
scopic in size.
Psoroptic mites do not burrow
in the skin of the host. Instead, by
pricking the skin to feed, they
cause serum to ooze from the wounds.
Accumulation of serum causes the for-
mation of scabs. It occurs almost
exclusively on the wooled parts of
the body where it produces large,
crusted lesions. Psoroptes infesta-
tions eventually may involve large
skin areas. The coat of the sheep
becomes ragged, and "tags" of wool are
torn out or rubbed away by the sheep.
Psoroptes ovis causes severe
debility, extensive loss of wool, and
in severe cases, deaths of animals
are not uncommon.
The life cycle requires about
two weeks and the infestation can
build rapidly. Psoroptes mites occur
abundantly under the scabs. Infested
sheep rub and scratch because of the
severe irritation, and this results in
rapid spread of the disease to other
animals.
Chorioptic Mange
This form of mange is probably
the most widespread in sheep in the
United States. Chorioptes mites
(Figure 37) live on the surface of
the skin and feed on scurf and skin
secretions. Although it sometimes
causes considerable irritation to the
host, the only noticeable skin lesions
occur on the scrotum of rams. Infested
sheep may often be observed biting or
licking their lower legs and feet.
The areas of the body on which this
mite is found are those haired areas
of the legs, face, and scrotum having no
wool. Little damage results to the
fleece and little weight is lost by
fattening lambs.
Control of Mange Mites
Dipping is the preferred method
of treatment for mange control in sheep.
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Figure 37~ ChorLoptes bovis, a mange
mite. Microscopic in size.
Current state and federal regulations	with or exposed to Psoroptes must be
concerning treatment of sheep infected	followed.
U.S. GOVERNMENT PRINTING OFFICE: 1981-680-146/73 Region No
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