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The
Western Treehole Mosquito (Aedes
sierrensis) is one of 53 types of mosquitoes that occur in
California. This mosquito is brightly marked with white scales
which contrast with its dark body. It also has an unbanded
proboscis (beak), white banded tarsi (feet) and a pointed tipped
abdomen. The
Western
Treehole Mosquito (Aedes sierrensis) received its name because the
immature stages are frequently found in water contained in rot holes of trees
such as oak, laurel, madrone, eucalyptus and other local species.
This mosquito is found in most California counties
and is the primary vector of
Dog
Heartworm disease in the Western United States.
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Adult Daily Activity:
Adults begin to emerge with the advent of the spring
equinox, requiring a 12 hour day length to trigger emergence.
Males tend to hover around potential hosts of the female, seizing her in
flight when she approaches, to mate with her. Male mating swarms also
occur in the shaded areas of this mosquitoes habitat. Adults can live
up to several months depending on temperature, humidity and other climactic
factors. They are
frequent pests in residential and recreational areas April through August
where large numbers of trees are present.
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Adult Flight Range:
This mosquito has a limited flight range staying very
close to its breeding site.
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Adult Feeding:
Adults feed predominantly on small mammals but will feed
on large mammals and humans when available. Peak feeding activity occurs at dusk, although host
feeding does sometimes occur during the day and night. Treehole
Mosquitoes prefer to feed outdoors (but sometimes enter homes) during the
mid-morning and late afternoon. Like all species of mosquitoes, only
the female mosquito takes a blood meal (bites).
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Eggs and Larvae:
Eggs are laid
individually inside moist treeholes, crotches of trees, and containers with
damp leafy debris. Eggs usually hatch the next season following
flooding with early winter rainfall. It should
be noted that the eggs of this species can survive for many years before
hatching, with only part of each batch hatching during a single season.
Larval development can take ten days to five months to complete, depending
on quantity of rainfall and other environmental conditions.
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DISEASES TRANSMITTED
Western Treehole Mosquitoes are a serious pest problem when they are
present in large numbers. This mosquito is the primary vector of
Dog Heartworm Disease
in the coastal and foothill communities of California.
DOG
HEARTWORM
Dog Heartworm Disease is a clinical
condition in dogs caused by a roundworm, Dirofilaria immitis, which
resides within the dog’s heart and lungs. This disease, a serious and
possibly fatal veterinary problem, is associated with dogs, coyotes and
foxes. Canine Heartworm is transmitted by the bite of an infected
Western
Treehole Mosquito.
The adult worm lives in the right side of
the heart and the adjacent large blood vessels and lungs, where it may attain a
length of 6-12 inches.
Many other mosquito species feed on dogs,
but the
Western
Treehole Mosquito is the most common carrier of heartworm.
The outward symptoms of the disease are
not noticeable in most cases until reduced blood flow caused by adult worms
damages the heart, lungs, liver and kidneys. Advanced symptoms of
heartworm may include: rapid tiring, shortness of breath, chronic soft dry
cough, listlessness and weight loss.
If you live in or travel to areas where
treehole mosquitoes occur, check with your veterinarian regarding treatment and
prevention. Drugs are available to prevent the disease, and it is curable
if diagnosed in the early stages.
In the San Francisco Bay area, the time of highest risk
for dogs to contract heartworm is April through August; however, unseasonable
rainfall may extend this period.
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DOG
HEARTWORM LIFE CYCLE
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DOG HEARTWORM RISK CHART
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A dog
already infected with heartworm is bitten by a mosquito and infects the
mosquito with microfilariae (very small worms).
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Area
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Outdoor Dog
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Indoor Dog
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The now
infected mosquito bites an uninfected dog transmitting Heartworm Disease to
that dog.
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Heavily Wooded (Wet)
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High
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Moderate
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The
microfilariae work their way to the heart and adjacent large blood vessels,
through the blood stream, where they continue to grow. As adults they reproduce
more microfilariae and…
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Heavily Wooded (Dry)
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Moderate
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Moderate
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The
cycle continues . . .
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Not
Wooded (Urban)
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Low
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Very Low
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For more information on Dog
Heartworm contact your local veterinarian
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Photo of Treehole Mosquito courtesy of Contra
Costa MVCD |
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WESTERN TREEHOLE
MOSQUITO LIFE
CYCLE |
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Western Treehole Mosquitoes have four life stages: egg, larva,
pupa, and adult. The immature stages need standing water to complete
their life cycle.
After an adult female lays her eggs they hatch into
larvae (wrigglers), which feed on small organic particles and microorganisms
in the water. Feeding occurs when they hang from the water's surface by
the tip of their tail (siphon) or by browsing along the bottom of their
habitat. Because they are air breathing organisms they must return to the water's surface to
breathe. Larval development varies from ten days to five months
depending on weather conditions with developmental completion occurring
around the spring equinox (late March). At the end of the larval
stage, the mosquito molts and becomes the aquatic pupa (tumbler). The
pupa is active only if disturbed, for this is the resting stage where the
larval form is transformed into the adult. This can take four or more
days during which time feeding does not occur. When the transformation
is completed, the new adult splits the pupal skin and emerges.
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