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University
of Rhode Island GreenShare Factsheets
Mosquitoes
Diptera:
Culicidae
Mosquitoes are insects in the order Diptera (flies), which
have only a single pair of wings. The wings of mosquitoes are
narrow and have a fringe of scales on the margins and veins.
Mosquitoes have three pairs of long, slender legs and two long
antennae. The mouthparts of mosquitoes form an elongate beak
called a proboscis. Female mosquitoes use this proboscis to
intake a blood meal.
Eastern Equine Encephalitis (EEE) is caused by a virus
that is transmitted by mosquitoes. It is a disease that in
most years remains in bird populations and is non-fatal to
native birds, although it may be fatal to horses and other
animals. EEE is established in most eastern seaboard states
and is usually associated with hardwood swamps. This habitat
is home to numerous species of mosquitoes which feed only on
birds. These species of mosquitoes maintain the virus in the
wild by transmitting the virus from bird to bird. During years
when mosquito populations are excessive, the numbers of infected
birds and infected mosquitoes rise. This elevates the probability
that other mosquito species will acquire the EEE virus. Although
EEE can be fatal to humans, it is extremely rare. On average,
15 human cases are documented nationwide per year. In other
countries, mosquitoes are responsible for transmitting diseases
such as malaria, yellow fever, dengue fever and filarial worms.
An average of 2 million people die each year from malaria,
while another 400 million are infected. Mosquitoes are also
responsible for transmitting canine heartworm to dogs.
Mosquitoes go through several stages of development. The
egg is the first stage, laid by the adult female. Depending
on the species of mosquito, eggs are either laid singly on
the water, on a substrate above the water or in a large batch
on the water called egg rafts. Eggs laid on solid substrates,
such as mud, hatch when they are flooded with water. This is
typical of saltmarsh mosquitoes (Aedes sollicitans) and
the temporary pool mosquito (Aedes vexans), where these
eggs can remain viable for several years until the next flooding.
The second stage of development
is the larva. Unlike the egg stage, larvae must always live
in the water to survive.
Larvae swim at the water surface and intake air through a snorkel-like
device called a siphon. Larvae will dive below the surface
when disturbed, but will return to the surface in order to
breath. The characteristic s-shaped motion of swimming larvae
gives them their common name "wiggler." Larvae are filter feeders,
eating organic matter in the water which they collect with
their bristle-like mouthparts.
The third stage of development
is the pupa. Pupae are comma-shaped and stay at the water
surface. If disturbed, they
tumble downward to escape, giving them the common name "tumblers." Pupae
do not feed, and this stage lasts only two or three days. Both
larvae and pupae are subject to heavy predation. Typically,
the 100-400 eggs laid by a female only result in a few adults
developing successfully.
In as little as seven to ten days, some mosquitoes can
develop from egg to adult. Adult behaviors vary depending upon
the species. Some breed and live near water, others may fly
considerable distances from a breeding site to seek a blood
meal. Some species are only active at dusk, while others seek
blood meals during daylight hours. Some species prefer to bite
birds, some prefer mammals, and others seek reptiles or amphibians.
Only the females seek blood, which they need as a protein source
to produce eggs. Males, as well as females, feed on flower
nectar or plant juices for energy for flight.
Mosquitoes breed in areas where there is standing water
or temporary pools. Mosquitoes commonly breed in saltmarshes,
swamps and areas flooded by snow melts and spring rains. However,
a small collection of water around a home can breed thousands
of mosquitoes. Some common sites are bird baths, roof gutters,
catch basins, rain barrels, swimming pools, wading pools, cesspools,
septic tanks, tires, paint buckets, tin cans, yard debris,
tree holes and anywhere that holds a small collection of water.
There are three types of control
strategies targeting mosquitoes. The best of these methods
is source reduction.
Source reduction is the elimination or manipulation of aquatic
habitats known to produce mosquitoes. An example of this is
eliminating small collections of water around the home. The
second most common method is mosquito larviciding. This refers
to applying environmentally-benign products to kill larvae
(the aquatic stage). An example of this is the bacteria B.t.i, "mosquito
dunks," which can be purchased in stores. Mosquito dunks are
not harmful to fish, animals or humans. The third, and least
preferred method of control, is mosquito adulticiding. This
requires the use of broad-spectrum insecticides, which can
be harmful to fish, birds and other animals.
One of the easiest and surest ways to control mosquitoes
around the home is to eliminate standing-water breeding sites.
Containers such as wading pools or bird baths should be flushed
weekly with clean water. Filtering systems for swimming pools
should keep a swimming pool free from immature mosquitoes.
Seal openings to standing-water sources such as septic tanks
or rainwater barrels. Search for and eliminate standing-water
sources. Old tires or discarded containers of most any sort
can collect water and attract the female mosquito for her egg
laying. One tire holds enough water to breed thousands of mosquitoes.
Drainage ditches, pools with lots of vegetation and sites such
as roof gutters and storm drains, which occasionally hold water,
can breed mosquitoes. Areas that contain fish and other natural
enemies of mosquito larvae, like amphibians and insects, are
not effective breeding sites because these animals eat the
larvae. If waterways are clogged with vegetation, mosquitoes
can survive. Check natural sites like holes in trees or stumps
where water can accumulate, and fill or prevent entry by adult
mosquitoes.
Some species of mosquitoes are capable of flying long
distances. An example of this is the saltmarsh mosquito Aedes
sollicitans, which can be found miles away from a possible
breeding site. Large populations of eggs of this species of
mosquito are hatched during monthly high tides, which results
in large numbers emerging all at once and searching for blood
meals. If you have property close to these areas, you may not
be able to effectively manage the source of the problem yourself.
It may be necessary to contact your local town hall or mosquito
control office to devise a community-based control strategy.
However, it is always important to follow proper preventive
measures to reduce exposure to biting mosquitoes.
• Maintain screens on doors
and windows
• Wear long sleeves and
long pants
• Avoid heavily shaded areas
• Use insect repellants containing
DEET
• Limit outdoor evening
activities
Although mosquitoes have many natural enemies, they are
not an effective control measure. Although birds and bats feed
on mosquitoes, making nest or roost areas for these predators
does not provide adequate mosquito reduction. The mosquito
fish, Gambusia, and guppies are also known to eat mosquito
larva, and can be purchased for stocking ponds or pools. However,
these fish cannot survive in temporary pools or standing water,
where the larvae are most likely to breed.
Several types of traps which claim to provide mosquito
control are available. However, most of these are not effective
in controlling mosquito populations. Ultraviolet lights and
bug zappers are widely advertised--however they attract very
few mosquitoes and should not be used for mosquito reduction.
Other mosquito traps are also becoming available and may reduce
mosquito populations if used correctly. However, some of these
traps may be very expensive.
The use of toxic insecticides indoors is not a safe method
of mosquito control. It is best to make sure all screens on
windows and doors are maintained to keep mosquitoes from entering.
A great deal of research has gone into finding and developing
effective insect repellents. Some compounds that were once
recommended have been removed from the market because of possible
side effects upon humans. Repellents containing DEET (N-diethyl-meta-toluamide)
are the most effective and commonly used repellents. DEET is
very effective for most people. Research has shown that products
containing DEET in concentrations higher than 30% are unnecessary
and increase the possibility of adverse skin reactions. Some
people show allergic sensitivity to DEET, particularly in higher
concentrations. Before using a repellent, check your personal
sensitivity. Be very careful not to use DEET repellents around
the eyes, nose or mouth. Repellents containing DEET should
not be used on very small children. Repellents containing natural
products such as clove oil, citronella, peppermint or combinations
of these and other odors are also available, and may provide
some temporary repellency. Other products such as citronella
candles and mosquito coils may also provide additional protection.
By Kristen Bartlett, 1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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