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Insect
Facts: Mosquitoes |
No-See'ums
| Flies Diseases:
West Nile Virus | Malaria
| Yellow Fever |
Encephalitis
| Dengue Fever
Disease Facts:
West Nile Virus &
Encephalitis Fact Sheet
Insect
Facts:
Mosquitoes:
How
Mosquitoes Work by Craig C. Freudenrich, Ph.D.
It's
summer time. You're out in your backyard enjoying the sun and grilling
your dinner. Ouch! You look down at your arm and see a painful,
swelling mosquito bite. Moments later, you feel another one bite
you. What are these pesky insects? Why do they bite? Do they carry
diseases? What can you do to protect yourself?
In
this edition of HowStuffWorks, we'll take a close-up look at mosquitoes
-- how they breed,
how
they bite, what diseases they carry and what you can do to control
them.
The
word "mosquito" is Spanish for "little fly,"
and its use dates back to about 1583 in North America (Europeans
referred to mosquitoes as "gnats"). Mosquitoes belong
to the order Diptera, true flies. Mosquitoes are like flies in that
they have two wings, but unlike flies, their wings have scales,
their legs are long and the females have a long mouth part (proboscis)
for piercing skin.
Mosquitoes
are insects that have been around for over 30 million years. And
it seems that, during those millions of years, mosquitoes have been
honing their skills so that they are now experts at finding people
to bite. A mosquito has a battery of sensors designed to track their
prey, including:
Chemical
sensors -- mosquitoes can sense carbon dioxide and lactic acid
up to 100 feet (36 meters) away. Just about any mammal or bird gives
off these gases as part of its normal breathing. Certain chemicals
in sweat also seem to attract mosquitoes (people who don't sweat
don't get nearly as many mosquito bites).
Visual
sensors -- if you are wearing clothing that contrasts with the
background, and especially if you move while wearing that clothing,
mosquitoes can see you and zero in on you. It's a good bet that
anything moving is "alive", and therefore full of blood,
so this is a good strategy.
Heat
sensors -- Mosquitoes can detect heat, so they can find warm-blooded
mammals and birds very easily once they get close enough.
Something
with this many sensors sounds more like a military aircraft than
an insect. That's why mosquitoes are so good at finding and biting
you! As we'll see later, one of the only ways to stop mosquitoes
from finding you is to confuse their chemical receptors with something
like DEET.
Like
all insects, adult mosquitoes have three basic body parts:
Head
- This is where all the sensors are, along with the biting aparatus.
The head has two compound eyes, antennae to sense chemicals and
the mouth parts called the palpus and the proboscis (only females
have the probiscus, for biting).
Thorax
- This segment is where the two wings and six legs attach. It contains
the flight muscles, compound heart, some nerve cell ganglia and
trachioles.
Abdomen
- This segment contains the digestive and excretory organs.
The
parts of a mosquito
There
are over 2,700 species of mosquitoes in the world, and there are
13 mosquito genera (plural for "genus") that live in the
United States. Of these genera, most mosquitoes belong to three:
Aedes
- These are sometimes called "floodwater" mosquitoes because
flooding is important for their eggs to hatch. Aedes mosquitoes
have abdomens with pointed tips. They include such species as the
yellow-fever mosquito (Aedes aegypti) and the Asian tiger mosquito
(Aedes albopictus). They are strong fliers, capable of travelling
great distances (up to 75 miles/121 km) from their breeding sites.
They persistently bite mammals (especially
humans),
mainly at dawn and in the early evening. Their bites are painful.
Anopheles
- These tend to breed in bodies of permanent fresh water. Anopheles
mosquitoes also have abdomens with pointed tips. They include several
species, such as the common malaria mosquito (Anopheles quadrimaculatus),
that can spread malaria to humans.
Culex
- These tend to breed in quiet, standing water. Culex mosquitoes
have abdomens with blunt tips. They include several species such
as the northern house mosquito (Culex pipiens). They are weak fliers
and tend to live for only a few weeks during the summer months.
They persistently bite (preferring birds over humans) and attack
at dawn or after dusk. Their bite is painful.
Some
mosquitoes, such as the cattail mosquito (Coquilettidia perturbans),
are becoming more prevalent pests as humans invade their habitats.
Let's
examine how mosquitoes live and breed.
Life
Cycle and Breeding Like all insects, mosquitoes hatch from eggs and go through several
stages in their life cycle before becoming adults. The females lay
their eggs in water and the larva and pupa stages live entirely
in water. When the pupa change into adults, they leave the water
and become free-flying land insects. The life cycle of a mosquito
can vary from one to several weeks depending upon the species (the
adult, mated females of some species can survive the winter in cool,
damp places until spring, when they will lay their eggs and die.)
Egg All mosquitoes lay eggs in water, which can include large bodies
of water, standing water (like swimming pools) or areas of collected
standing water (like tree holes or gutters). Females lay their eggs
on the surface of the water, except for Aedes mosquitoes, which
lay their eggs above water in protected areas that eventually flood.
The eggs can be laid singly or as a group that forms a floating
raft of mosquito eggs (see Mosquito Life Cycle for a picture of
an egg raft). Most eggs can survive the winter and hatch in the
spring.
Larva Identifying
Larvae You
can distinguish the larvae of various mosquito species. Anopheles
larvae lie parallel to the
surface
of the water, while larvae of Aedes and Culex extend down into the
water (the air tubes of Culex are longer than those of Aedes).
The
mosquito eggs hatch into larvae or "wigglers," which live
at the surface of the water and breathe through an air tube or siphon.
The larvae filter organic material through their mouth parts and
grow to about 0.5 to 0.75 inches (1 to 2 cm) long; as they grow,
they shed their skin (molt) several times. Mosquito larvae can swim
and dive down from the surface when disturbed (see Mosquito Life
Cycle for a Quicktime movie of free-swimming Asian tiger mosquito
larvae). The larvae live anywhere from days to several weeks depending
on the water temperature and mosquito species.
Pupa The
mosquito larvae and pupae are important food sources for fish in
aquatic ecosystems. After
the fourth molt, mosquito larvae change into pupae, or "tumblers,"
which live in the water anywhere from one to four days depending
on the water temperature and species. The pupae float at the surface
and breathe through two small tubes (trumpets). Although they do
not eat, pupae are quite active (see Mosquito Life Cycle for a Quicktime
movie of free-swimming Asian tiger mosquito pupae). At the end of
the pupal stage, the pupae encase themselves and transform into
adult mosquitoes.
Adult Inside the pupal case, the pupa transforms into an adult. The adult
uses air pressure to break the pupal case open, crawls to a protected
area and rests while its external skeleton hardens, spreading its
wings out to dry. Once this is complete, it can fly away and live
on the land.
One
of the first things that adult mosquitoes do is seek a mate, mate
and then feed. Male mosquitoes have short mouth parts and feed on
plant nectar. In contrast, female mosquitoes have a long proboscis
that they use to bite animals and humans and feed on their blood
(the blood provides proteins that the females need to lay eggs).
After they feed, females lay their eggs (they need a blood meal
each time they lay eggs). Females continue this cycle and live anywhere
from many days to weeks (longer over the winter); males usually
live only a few days after mating. The life cycles of mosquitoes
vary with the species and environmental conditions.
Mosquito
Bites As mentioned before, only female mosquitoes bite. They are attracted
by several things,
including
heat (infrared light), light, perspiration, body odor, lactic acid
and carbon dioxide. The female lands on your skin and sticks her
proboscis into you (the proboscis is very sharp and thin, so you
may not feel it going in). Her saliva contains proteins (anticoagulants)
that prevent your blood from clotting. She sucks your blood into
her abdomen (about 5 microliters per serving for an Aedes aegypti
mosquito).
Photo
courtesy Centers for Disease Control & Prevention, photographer
Jim Gathany This female Anopheles gambiae mosquito is feeding. You can see the
blood swelling her abdomen.
If
she is disturbed, she will fly away. Otherwise, she will remain
until she has a full abdomen. If you were to cut the sensory nerve
to her abdomen, she would keep sucking until she burst.
After
she has bitten you, some saliva remains in the wound. The proteins
from the saliva evoke an immune response from your body. The area
swells (the bump around the bite area is called a wheal), and you
itch, a response provoked by the saliva. Eventually, the swelling
goes away, but the itch remains until your immune cells break down
the saliva proteins.
To
treat mosquito bites, you should wash them with mild soap and water.
Try to avoid scratching the bite area, even though it itches. Some
anti-itch medicines such as Calamine lotion or over-the-counter
cortisone creams may relieve the itching. Typically, you do not
need to seek medical attention (unless you feel dizzy or nauseated,
which may indicate a severe allergic reaction to the bite).
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Myths
Several
natural or man-made products have been touted as mosquito
repellents or effective in mosquito control. Citronella oil,
which is a product of several types of plants that can be
made into candles or burned directly, is an effective mosquito
repellant in high concentrations, but individual citronella-producing
plants do not make enough oil to effectively repel mosquitoes.
Ultraviolet lights, as used in bug zappers, and ultrasonic
devices are not effective. Also, mosquitoes are not a significant
portion of the diets of Purple Martin Birds or bats.
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No-See'ums
a.k.a. Sand Flies:
Often
called "punkies", "no-see'ums" or sand flies,
the biting midges are viscious where they occur. They are often
more troublesome than mosquitoes because they can easily enter dwellings
through ordinary 16-mesh window screen. The presence of these insects
can decrease property values and severly hamper use of recreational
areas. Vacationers and campers literally have been driven away from
areas by these tiny biters. Snad flies can also cause loss to cattlemen
in terms of annoyance to cattle and transmission of various nematode
diseases.
Sand
flies are members of the insect order Diptera and undergo a complete
development with egg, larva, pupa, and adult forms. The adults are
less than 1/16-inch long, dark gray to black in color. and have
one pair of wings, which are spotted. The sand flies breed predominantly
in salt marshes; however some species that are found inland breed
in fresh water areas and tree holes.
Larvae
of sand flies are found in mud, sand, and deris around the edges
of ponds, springs, lakes, creeks, and in tree holes or slime covered
bark. In the water they are free swimmers and are commonly found
on floating twigs or leaf trash. The larvae pupate on floating debris
or at the water's edge. The adult females, like mosquitoes, require
blood to mature the eggs. Males do not bite. Sand fly larvae can
be found in marshes the year-round; however, the period of greatest
adult activity is June to August.
Sand
fly activity is associated with air movement. Adults of most species
seldom bite when there is air movement. Sand flies are also sensitive
to temperature. Animals having high body temperature are attractive
to great numbers of female sand flies. Persons performing hard labor
out-of-doors frequently are severely annoyed by these insects.
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Flies:
A
SINGLE FLY CAN CONTAMINATE FEED/FOOD
WITH ENOUGH BACTERIA TO CAUSE ILLNESS
The
fly is an enemy because it is one of the biggest disease carriers
in existance. Moist, warm, decaying material protected by sunlight
is favored for fly eggs to hatch and in only 8 short hours for fly
larvae or maggots to grow. An uncovered garbage can is an ldeal
breeding place. Flies feed and reproduce on filth, decaying matter,
and water.
Flies
are tranmitters of disease primarily because they feed on human
and animal wastes. The dangerous bacteria present in these wastes
stick to the mouth, footpads and hairs of flies and may then be
deposited in feed intended for animal consumption. Fly feces, which
contain disease-bearing organisms, can also contaminate human food.
Flies defecate every four to five minutes. And since flies have
no teeth and must take their nourishment in liquid form, they spit
on solid food and let the dissolve before consuming it. Fly spittle,
or vomitus, is swarming with bacteria and contaminates feed and
areas where feed is stored.
A
fly can infect feed/food by merely landing on it.
Flies
can enter a building that has openings not much larger than the
head of a pin.
Although
they rarely travel very far from where they are hatched, flies may
be lured to the sources of attractive odors. Flies may also be carried
long distances by air current.
One
female fly can produce thousands of offspring in a single breeding
season. flies have favorite resting places. They are especially
fond of places protected from the wind and on edges such as garbage
can rims and electric wires
Flies
carry bacteria that can cause many diseases known and unknown to
man.
One
fly can carry over 33 million disease-causing microorganisms on
the inner and outer surfaces of its body.
There
are over 87,000 different fly species.
The
fly is one of the fastest flying insects.
A
fly's vision is sharp for only 24 to 36 inches.
One
successful hatch can result in well over 2 million flies.
One
season can breed as much as 25 generations.
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Flies:
A SINGLE
FLY CAN CONTAMINATE FEED/FOOD
WITH ENOUGH BACTERIA TO CAUSE ILLNESS
The
fly is an enemy because it is one of the biggest disease carriers in
existance. Moist, warm, decaying material protected by sunlight is
favored for fly eggs to hatch and in only 8 short hours for fly
larvae or maggots to grow. An uncovered garbage can is an ldeal
breeding place. Flies feed and reproduce on filth, decaying matter,
and water.
Flies
are tranmitters of disease primarily because they feed on human and
animal wastes. The dangerous bacteria present in these wastes stick
to the mouth, footpads and hairs of flies and may then be deposited
in feed intended for animal consumption. Fly feces, which contain
disease-bearing organisms, can also contaminate human food. Flies
defecate every four to five minutes. And since flies have no teeth
and must take their nourishment in liquid form, they spit on solid
food and let the dissolve before consuming it. Fly spittle, or
vomitus, is swarming with bacteria and contaminates feed and areas
where feed is stored.
A fly
can infect feed/food by merely landing on it.
Flies
can enter a building that has openings not much larger than the head
of a pin.
Although they rarely travel very far from where they are hatched,
flies may be lured to the sources of attractive odors. Flies may
also be carried long distances by air current.
One
female fly can produce thousands of offspring in a single breeding
season. flies have favorite resting places. They are especially fond
of places protected from the wind and on edges such as garbage can
rims and electric wires
Flies
carry bacteria that can cause many diseases known and unknown to
man.
One
fly can carry over 33 million disease-causing microorganisms on the
inner and outer surfaces of its body.
There
are over 87,000 different fly species.
The
fly is one of the fastest flying insects.
A
fly's vision is sharp for only 24 to 36 inches.
One
successful hatch can result in well over 2 million flies.
One
season can breed as much as 25 generations.
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Insect
Diseases: Aug
14, 2002
Florida
Reports 1st Human Case Of West Nile
By NEIL JOHNSON (TBO.COM)
TAMPA
- Health officials confirmed the first human case of West Nile virus
in Florida on Tuesday and expanded a health alert to four more counties,
including Sumter and Orange, bringing the total to six.
The
newest alert also covers Lake and Marion counties.
The
Sumter County man who tested positive for the mosquito-borne virus
may have been bitten in Louisiana, where 85 people have contracted
West Nile and seven have died.
"We
don't know for sure,'' said April Crowley, spokeswoman for the state
Department of Health.
Earlier
this week, a dead crow found five miles west of Brooksville in Hernando
County tested positive for West Nile.
Last
week, the Department of Health issued medical alerts for Escambia
and Volusia counties.
The
alerts are issued to advise people the virus is present in their
counties so that they can avoid mosquito bites, and also to prompt
doctors to be more aware of potential cases.
The
virus previously occurred in Africa, the Middle East, western Asia
and Europe. It was first discovered in this country in 1999. The
disease spreads when mosquitoes bite infected birds and then bite
a person. Humans cannot spread the disease.
Health
officials test dead birds, horses and chickens kept in outdoor cages
to monitor several mosquito-borne diseases including West Nile and
eastern equine encephalitis.
Although
Sumter was the only county in the newest list of counties put under
alert with a human case, birds, horses and chickens in the other
three have tested positive for West Nile.
In
Lake County, two birds and three horses have been found with the
virus. Marion had six horses and one bird. Orange had nine chickens,
a horse and two birds, and Sumter had one horse.
No
animal cases of West Nile have been found in Hillsborough, but eight
chickens have tested positive for the virus in Pinellas and one
bird in Pasco.
To
the south, Manatee has had a horse and a chicken with the disease.
Only
about 10 percent of people bitten by infected mosquitoes show any
symptoms, which are similar to the flu. Only about 1 in 200 people
develop encephalitis, a potentially fatal swelling of the brain.
So
far this year, fewer people have contracted West Nile in Florida
than in 2001.
"Last
year by this time, we had three human cases. We're seeing a little
more animal cases this year,'' Crowley said.
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| June
15, 2002
First
West Nile Case of the Year
Bay News 9
Pinellas
County is dealing with their first West Nile virus case of the year.
It
didnt come as a surprise to Pinellas County Mosquito Control
when a sentinel chicken tested positive for the virus.
Nancy
Page with mosquito control says, she knew it was a matter of time.
"We were expecting it eventually." she says. "We
had it come up last year in November (and) it was spreading throughout
the state this year, so we knew it would arise in Pinellas county
again this year."
The
chicken came from a St. Petersburg coop, which is one of the best
weapons in detecting mosquito-born diseases like WEST NILE.
Pinellas
County Mosquito Control has eight chicken coops across the county
that test the blood from sentinel chickens each week. Wednesday,
one of these samples tested positive.
WEST
NILE is transmitted from birds to mosquitoes, who can then pass
it on to humans.
The
virus first showed up in the U.S. in New York in 1999. Two years
later, Florida had its first case. While scientists don't know a
lot about WEST NILE, aerial spraying and fogging to control the
mosquito population seems to be the best way to fight it.
Looking
for recorded information on Florida cases of the West Nile virus?
Call the Department of Health Bureau of Epidemiology's Arboviral
Encephalitis and West Nile virus hotline at 1-888-880-5782.
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Sunday,
March 31, 2002
Polk
County Horse Tests Positive For West Nile Virus
The
disease is spread primarily through infected mosquitoes.
A horse in Polk City has been confirmed as this year's first local
casualty of the West Nile virus.
The
disease, carried by mosquitoes, can make humans ill but its
rarely fatal. According to The Ledger, as many as five other horses
have died in the last month after suffering symptoms common to the
virus. Polk County health officials say they're unaware of any other
local cases of disease.
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| Diseases:
Mosquitoes
can carry many types of diseases that are caused by bacteria, parasites
or viruses. These diseases include:
Malaria - Malaria is caused
by a parasite that is transmitted by an Anopheles mosquito. The
parasite grows in your bloodstream and can produce symptoms that
develop anywhere from six to eight days to several months after
infection.The symptoms include fever, chills, headaches, muscle
aches and general malaise (similar to flu symptoms). Malaria is
a severe disease that can be fatal, but can be treated with antimalarial
drugs and prevented by vaccinations. Malaria is prevalent in tropical
or sub-tropical climates.
Yellow Fever - Yellow fever
does not occur in the United States, but is prevalent in Africa
and is transmitted by the Aedes aegypti mosquito. Yellow fever produces
symptoms similar to malaria, but also includes nausea, vomiting
and jaundice. Like malaria, yellow fever can be fatal. There is
no treatment for the disease itself, only the symptoms. Yellow fever
can be controlled by vaccination and mosquito control.
Encephalitis - Encephalitis is caused by viruses that are transmitted
by mosquitoes such as the Aedes mosquitoes or Culiseta mosquitoes.
The symptoms of encephalitis include high fever, stiff neck, headache,
confusion and laziness/sleepiness. There are several types of encephalitis
that can be transmitted by mosquitos, including St. Louis, Western
equine, Eastern equine, La Crosse and West Nile. West Nile encephalitis
is on the rise in the eastern United States, which has raised concerns
about mosquito control (see Overview of West Nile Virus for more
information).
Dengue Fever - Dengue fever is transmitted by the Asian tiger
mosquito, which is native to East Asia and was found in the United
States in 1985. It is also transmitted by Aedes aegypti in the tropics.
Dengue fever is caused by a virus that produces a range of illnesses,
from viral flu to hemorrhagic fever. It is especially dangerous
for children (see Dengue Fever & Dengue Hemorrhagic Fever for
more information).
The best way to reduce mosquito-borne diseases is through mosquito
control and personal protection.
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WEST
NILE VIRUS HITS
FLORIDA
Its
just a short time before the VIRUS spreads further.
NOW!!
is the time to protect your horses, cattle, poultry and children
from this potentially deadly virus
WEST
NILE VIRUS & ENCEPHALITIS FACT SHEET
What
is West Nile encephalitis?
"Encephalitis"
is an inflammation of the brain and can be caused by viruses and
bacteria including viruses transmitted by mosquitoes. West Nile
encephalitis is an infection of the brain caused by West Nile virus.
It is closely related to St. Louis encephalitis virus found in the
United States.
How
long has West Nile virus been in the United States and where did
it come from?
It
is not known how long it has been In the U.S. CDC scientists believe
the virus has been in the eastern U.S. since the early summer of
1999, possibly longer. West Nile virus has been commonly found in
humans and birds and other vertebrates in Africa, Eastern Europe,
West Asia, and the Middle East, but has not previously been documented
in the Western Hemisphere, It is not known from where the U.S. virus
originated.
In
the Temperate Zone of the world (i.e., between latitudes 23.5 and
66.5 degrees north and south), West Nile encephalitis cases occur
primarily in the late summer or early Fall. In the southern climates
where temperatures are milder, West Nile virus ran be transmitted
year round.
What
Is the incubation period in humans (or time from infection to onset
of disease
symptoms) for West Nile encephalitis?
Usually
5 to 15 days.
What
are the symptoms of West Nile encephalitis?
Mild
infections have symptoms that include fever, headache, and body
aches, often with skin rash and swollen lymph glands. More severe
infection may be marked by headache, high fever, neck stiffness,
stupor, disorientation, coma, tremors, convulsions, muscle weakness,
paralysis, and rarely death. If you believe you have West Nile,
seek medical care as soon as possible.
Is
a woman's pregnancy at risk if she gets West Nile encephalitis?
There
is NO documented evidence that a pregnancy is at risk due to infection
with West Nile
virus.
How
do people get West Nile encephalitis?
The
bite of a mosquito that is infected with West Nile virus is all
it takes to transmit the infection. Mosquitoes become infected when
they feed on infected birds. After an incubation period of 1 to
2 weeks, infected female mosquitoes can then transmit West Nile
virus to humans and animals while biting. The mosquitoes and the
bites they cause do not differ from those bites of an uninfected
mosquito.
Can
you get West Nile encephalitis from an infected person or an infected
bird?
NO.
West Nile encephalitis is NOT transmitted from person-to-person.
For example, you cannot get West Nile virus from touching or kissing
a person who has the disease, or from a health care worker who has
treated someone with the disease.
There
is NO evidence that a person can get the virus from handling live
or dead infected birds. However, avoid contact with any dead bird
or animal, by using gloves or plastic bags to place it in a garbage
can.
Can
you get West Nile virus directly from other insects or animals?
Ticks
infected with West Nile virus have been found in Asia and Africa.
Their role in the transmission and maintenance of the virus is uncertain.
However, there is no information to suggest that ticks transmitted
West Nile virus to patients in the New York area outbreak. Infected
mosquitoes are the primary source for West Nile virus and have been
found to cause the recent outbreak in the New York City metropolitan
area.
Although
other animals (e.g., horses and dogs) may become infected with West
Nile Virus, there have been no reports of the disease being transmitted
from the infected animal to humans or other animals. Contact a Veterinarian
if you have questions about pets or other animals.
How
is West Nile encephalitis treated?
There
is NO specific therapy or vaccine for West Nile infection. In more
severe cases, intensive supportive therapy is indicated which includes
hospitalization.
Who
is at risk for getting West Nile encephalitis?
All
residents of areas where virus activity had been identified are
at risk of getting West Nile encephalitis; persons greater than
50 years of age have the highest risk of severe disease.
What
can I do to reduce my risk of becoming infected with West Nile virus?
Check and repair window and door screens.
Remove containers
that collect standing water such as cans, bottles, buckets, toys
and old tires.
Remove standing
water from kiddy pools, pool covers, flowerpots and plant containers.
Drill holes in the
bottoms of recycling containers and other receptacles that are left
outdoors.
Check and repair
window and door screens.
Remove containers
that collect standing water such as cans, bottles, buckets, toys
and old tires.
Remove standing
water from kiddy pools, pool covers, flowerpots and plant containers.
Drill holes in the
bottoms of recycling containers and other receptacles that are left
outdoors.
Minimize time spent
outdoors during the dawn and dusk hours when mosquitoes are out
in greater numbers.
If
you are outdoors in the evening hours, wear long-sleeved shirts
and long pants.
Apply an appropriate insect repellent. If you choose to do this,
read and follow carefully the manufacturer's DIRECTIONS FOR USE,
as printed on the product. Repellents may irritate, the eyes and
mouth, so avoid applying repellent to the hands of children. Insect
repellents should not be applied to very young children (less than
3 years old).
The
Bug-Slayer® Mosquito, No-see-um, Insect Automatic Mist Delivery Control System.
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