Why are Mosquitos a Concern?
Mosquitos are known carriers of many diseases globally including West Nile Virus. Currently, West Nile Virus is causing concern in the USA and Canada.
For information on West Nile Virus, please refer to the following Health Canada fact sheets on the web site hosted by the Population and Public Health Branch’s Centre for Infectious Disease Prevention and Control
www.westnilevirus.gc.ca  .
The Lifecycle of Mosquitos
Because they are aquatic in their immature stages, all mosquitos must
have water in which to develop. The larvae cannot develop in tall grass
or shrubbery, although the adults may be found resting in these spots during
the day.
Eggs
The
females of some mosquito species lay their eggs directly on the surface
of water, in a raft of between 100 and 400 eggs. The eggs hatch in a
day or so into larvae. Other species leave their eggs in a spot that
will flood later, such as mud at the edge of a drying pond.
Larvae
Mosquito
larvae look like worms, with no legs or wings; they are often known as "wigglers".
They need to breathe air, so they hang from the water surface and feed
there by filtering small particles from the water, but will dive to the
bottom for short periods to feed or escape capture. They grow rapidly
during this stage, molting four times during the next few days. On the
fourth molt, they become pupae, where they form legs and wings.
Pupae
The
comma-shaped pupae are also known as "tumblers" because they somersault
in the water when disturbed. They cannot eat and must breathe air through
two tubes on their backs. The mosquitos grow inside the pupae. When
they are ready, in about two days or so, they split the pupal skin and
emerge as adults.
Adults
The
adult mosquitos rest on the surface of the water until they are strong
enough to fly, at which time they will search for something to eat. This
entire life cycle from egg to adult can be completed in less than 10
days when the temperature is favorable.
Both male and female mosquitos feed on nectar from flowers for their
energy, but male mosquitos feed exclusively on nectar, while the female
must have blood to produce her eggs. Most mosquitos in the wild feed
on animals found in their habitat and not on people. Some species prefer
birds as hosts, while others accept many animals as hosts, including
people.
These species are considered pests whenever there are many of
them in areas used by people, such as camp sites or picnic grounds. The
female mosquito may live for as long as three weeks during the summer,
and any female that lives long enough to feed on blood more than once
has the potential to transmit blood-borne diseases from one animal or
person to another.
The females are very specific about where they lay their eggs, and pick
water suitable for their offspring. Although most mosquito species breed
in clean water in the wild, many of the species that breed near your
home tolerate polluted water.
Most of the 75 mosquito species found in Canada survive the winter as
dormant, fertilized eggs but in a few species, such as Culex pipiens and Anopheles
punctipennis , it is the fertilized females that survive the winter
in cool, sheltered places such as caves, animal burrows, cellars and
sewers, to take their first blood meals and lay eggs in the spring.
Mosquitos that Breed Around the Home
Mosquitos of some species can fly far from their breeding sites, so their presence
in your neigbourhood does not always mean they have bred or will breed there.
However, certain mosquitos are considered domestic species because they breed
around the home in small, artificial containers such as bird baths and eavestroughs.
Females of some of them will feed on people, will enter your home for a meal
and are significant pests.
Culex pipiens
The northern house mosquito, Culex pipiens is the most common mosquito
in urban and suburban areas of eastern Canada and British Columbia. The larvae
can be found in artificial containers and ditches, and also in natural rain
puddles and ponds. They thrive in water polluted with organic wastes. The females
feed mainly at night and mostly on birds, but they will also bite people both
outdoors and indoors.
The tendency of these females to feed on people or birds,
the wild hosts of West Nile Virus, makes Cx. pipiens the most likely
vector of West Nile Virus in North America, both from birds to birds and from
birds to people. A closely related species, Cx. restuans , is found
in eastern Canada and the prairie provinces. The larvae are found in similar
sites, but the females less commonly bite people.
Ochlerotatus triseriatus
The eastern tree-hole mosquito, Aedes triseriatus , another fairly
common pest around homes, lays its eggs in tree-holes in many hardwoods. The
eggs are laid just above the water line in the tree-hole. When rain raises
the water level, the eggs hatch. Tires containing decomposing organic material,
such as leaves, can simulate this habitat and may be used by the eastern tree-hole
mosquito as a breeding site. A single discarded tire in your yard can be the
source of thousands of tree-hole mosquitos over a summer.
Other Species
Larvae of Ochlerotatus atropalpus , which normally live in rock pools,
and those of Anopheles punctipennis , which normally live in ponds
and marshes, are sometimes found in artificial containers near dwellings. Females
of these species will bite people, and may be pests around your home. Larger
bodies of water on residential properties, such as ponds, snowmelt pools and
grassy ditches, may form breeding sites for many other species, too many to
name here. Some of these species are significant pests; others never bite people.
What You Can Do Around Your Home and Community
You and your neighbours can do several things to prevent mosquitos from breeding
near your homes and also to protect yourselves from mosquito bites.
Controlling Breeding Sites
- Since mosquitos breed in stagnant water, and can do so even in very small
quantities, remove any possible breeding areas where mosquitos could lay
eggs.
- Eliminate
sources of standing water in your yard (for example, flower pots, gardening
cans, wheelbarrows, puddles) and store items upside down that must remain
in your yard, such as boats and gardening containers.
- Empty tire swings of any water and, if possible, replace the swings with
other types.
- Cover any garbage, recycling or composting containers, to prevent water
from accumulating in them.
- Drill holes in the bottom of containers that must be left outdoors.
- Replace water in bird baths and outdoor pet dishes at least every week
to help eliminate stagnant water in them and also provide fresh water.
- Empty your rain barrel if the water is more than a week old.
- Keep your swimming pool aerated, cleaned and chlorinated, even if it
is not being used.
- Dump any water that collects on your swimming pool cover.
- Turn over plastic wading pools when they're not being used. Change the
water in your wading pool at least each week.
- Keep your gutters clean to prevent standing water.
- Check under shrubbery and lawn coverings for hidden containers.
- Use landscaping to eliminate water that collects in low areas on your
property. Mosquitos can develop in any puddle that lasts more than 7-10
days during the summer.
- Repair any leaks from outdoor water pipes, joints or hoses. Replace washers
on outdoor taps that drip.
Controlling Mosquito Larvae
Aquatic birds, frogs, fishes, beetles, water bugs and dragonflies eat many
mosquito larvae. As well, you might try aerating your ornamental pond.
Mosquito larvae may also be controlled with the bacterium Bacillus thuringiensis
var. israelensis (Bti), a naturally occurring microbe-based product.
Bti causes minimal impact to the environment and other insect and animal
species. Commercial Bti products are available for use in private ponds and
farm dugouts where no water flows out beyond the property limits.
Protecting Yourself
During mosquito season (May to September for most of Canada), limit outdoor
activities as much as possible between dusk and dawn, when mosquitos are the
most active. There are mosquito species that bite humans during the day, but
these have not been known to carry the West Nile Virus.
- Wear long pants and long sleeves, as well as shoes and socks when outdoors
for long periods of time, or when mosquitos are most active.
- Wear loose clothes made of tightly woven materials that keep mosquitos
away from the skin.
- Use mosquito netting when sleeping outdoors or in an unscreened structure
and to protect small babies when outdoors.
- If you choose to use an insect spray in the patio and garden area, be
sure to follow label directions carefully.
- Citronella candles used outdoors around patios, picnic tables and decks
to repel mosquitos are not very effective mosquito control options.
- Bug zappers (electrocutor traps) placed out of doors have not been proven
effective in reducing or eliminating mosquito populations.
- Electronic "mosquito repellers" that emit high frequency sound do not
repel mosquitos.
- Claims that certain plants placed around a porch or deck will repel mosquitos
are not supported by scientifically based test results.
- Repair or replace old and torn screens in doors, windows and vents that
no longer prevent mosquitos from entering your home. Repair any other
possible access points into your home.
- If mosquitos get into your home, you might find them resting on walls,
under sinks, in closets or the basement. If you use a commercial insect
spray, be sure to follow label instructions carefully.
Personal Insect Repellents
For information on the effective and safe use of personal insect repellents,
see Health Canada's fact sheet, Safety Tips on Using Personal Insect Repellents
found at www.westnilevirus.gc.ca .
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