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Pesticides
and Mosquito Control
Mosquito-borne
diseases affect millions of people worldwide each year. In the United
States, some species of mosquitoes can transmit diseases such as
encephalitis, dengue fever, and malaria to humans, and a variety
of diseases to wildlife and domestic animals. To combat mosquitoes
and the public health hazards they present, many states and localities
have established mosquito control programs. These programs, which
are based on surveillance, can include nonchemical forms of prevention
and control as well as ground and aerial application of chemical
and biological pesticides.
The
mission of the Environmental Protection Agency (EPA) is to protect
human health and the environment. EPA reviews and approves pesticides
and their labeling to ensure that the pesticides used to protect
public health are applied by methods that minimize the risk of human
exposure and adverse health and environmental effects. In relation
to mosquito control, the Agency also serves as a source of information
about pesticide and nonpesticide controls to address the concerns
of the general public, news media, and the state and local agencies
dealing with outbreaks of infectious diseases or heavy infestations
of mosquitoes. The following questions and answers provide some
basic information on mosquito control, safety precautions, and information
on insecticides used for mosquito control programs.
How
Does EPA Ensure the Safest Possible Use of Pesticides?
EPA must evaluate and register pesticides before they may be sold,
distributed, or used in the United States. The Agency is also in
the process of reassessing, and reregistering when appropriate,
all older pesticides (those registered prior to 1984) to ensure
that they meet current scientific standards. To evaluate a pesticide
for either registration or re-registration, EPA assesses a wide
variety of potential human health and environmental effects associated
with use of the product. The producer of the pesticide must provide
data from tests done according to EPA guidelines. These tests determine
whether a pesticide has the potential to cause adverse effects on
humans, wildlife, fish, and plants, including endangered species
and nontarget organisms. Other tests help to assess the risks of
contaminating surface water or ground water from leaching, runoff,
or spray drift. If a pesticide meets EPA requirements, the pesticide
is approved for use in accordance with label directions. However,
no pesticide is 100 percent safe and care must be exercised in the
use of any pesticide.
How
Are Mosquitoes Controlled with Pesticides and Other Methods?
The first step in mosquito control is surveillance. Mosquito specialists
conduct surveillance for diseases harbored by domestic and nonnative
birds, including sentinel chickens (used as virus transmission indicators),
and mosquitoes. Surveillance for larval habitats is conducted by
using maps and aerial photographs, and by evaluating larval populations.
Other techniques include various light traps, biting counts, and
analysis of reports from the public. Mosquito control programs also
put high priority on trying to prevent a large population of adult
mosquitoes from developing so that additional controls may not be
necessary. Since mosquitoes must have water to breed, methods of
prevention may include controlling water levels in lakes, marshes,
ditches, or other mosquito breeding sites, eliminating small breeding
sites if possible, and stocking bodies of water with fish species
that feed on larvae. Both chemical and biological measures may be
employed to kill immature mosquitoes during larval stages. Larvicides
target larvae in the breeding habitat before they can mature into
adult mosquitoes and disperse. Larvicides include the bacterial
insecticides Bacillus thuringiensis israelensis and Bacillus sphaericus,
the insect growth inhibitor methoprene, and the organophosphate
insecticide temephos. Mineral oils and other materials form a thin
film on the surface of the water which cause larvae and pupae to
drown. Liquid larvicide products are applied directly to water using
backpack sprayers and truck or aircraft-mounted sprayers. Tablet,
pellet, granular, and briquet formulations of larvicides are also
applied by mosquito controllers to breeding areas.
Adult
mosquito control may be undertaken to combat an outbreak of mosquito-borne
disease or a very heavy nuisance infestation of mosquitoes in a
community. Pesticides registered for this use are adulticides and
are applied either by aircraft or on the ground employing truck-mounted
sprayers. State and local agencies commonly use the organophosphate
insecticides malathion and naled and the synthetic pyrethroid insecticides
permethrin, resmethrin, and sumithrin for adult mosquito control.
Mosquito
adulticides are applied as ultra-low volume (ULV) sprays. ULV sprayers
dispense very fine aerosol droplets that stay aloft and kill flying
mosquitoes on contact. ULV applications involve small quantities
of pesticide active ingredient in relation to the size of the area
treated, typically less than 3 ounces per acre, which minimizes
exposure and risks to people and the environment.
What
Can I Do to Reduce the Number of Mosquitoes in and Around My Home?
The most important step is to eliminate potential breeding habitats
for mosquitoes. Get rid of any standing water around the home, including
water in potted plant dishes, garbage cans, old tires, gutters,
ditches, wheelbarrows, bird baths, hollow trees, and wading pools.
Any standing water should be drained, including abandoned or unused
swimming pools. Mosquitoes can breed in any puddle that lasts more
than 4 days. Make sure windows and screen doors are "bug tight."
Replace outdoor lights with yellow "bug" lights. Wear
headnets, long-sleeved shirts, and long pants if venturing into
areas with high mosquito populations, such as salt marshes or wooded
areas. Use mosquito repellents when necessary, always following
label instructions.
Should
I Take Steps to Reduce Exposure to Pesticides During Mosquito Control
Spraying?
Generally, there is no need to relocate during mosquito control
spraying. The pesticides have been evaluated for this use and found
to pose minimal risks to human health and the environment when used
according to label directions. For example, EPA has estimated the
exposure and risks to both adults and children posed by ULV aerial
and ground applications of the insecticides malathion and naled.
For all the exposure scenarios considered, exposures ranged from
100 to 10,000 times below an amount of pesticide that might pose
a health concern. These estimates assumed several spraying events
over a period of weeks, and also assumed that a toddler would ingest
some soil and grass in addition to dermal exposure. Other mosquito
control pesticides pose similarly low risks. (For more details on
health and environmental risk considerations, see the separate EPA
fact sheets on the specific mosquito control pesticides.)
Although
mosquito control pesticides pose low risks, some people may prefer
to avoid or further minimize exposure. Some common sense steps to
help reduce possible exposure to pesticides include:
Pay
attention to the local media for announcements about spraying and
remain indoors during applications in the immediate area.
People who suffer from chemical sensitivities or feel spraying may
aggravate a preexisting health condition, may consult their physician
or local health department and take special measures to avoid exposure.
Close windows and turn off window-unit air conditioners when spraying
is taking place in the immediate area.
Do not let children play near or behind truck-mounted applicators
when they are in use.
Where
Can I Get More Information?
For more information about mosquito control in your area, contact
your state or local health department.
Source:
CDC Office of Pesticide Programs
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