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Mosquito Control in

Maryland

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The Asian Tiger

Mosquito Control

Program

Description

Mosquito Control Program Description

Mosquito Biology

Mosquito Surveillance

Mosquito-Borne Disease Surveillance

Mosquito Control Options

Future Prospects and Program Issues

Program Description

The Maryland Department of Agriculture

(MDA), Mosquito Control Section, is

responsible for administering and

implementing mosquito control within the

State of Maryland. Typical projects

undertaken for mosquito control include

Public Health arboviral surveillance and

testing, mosquito population surveillance

activities, source reduction, biological

control initiatives, ground and aerial

application of insecticides and public

education. The Mosquito Control Program

has existed since July, 1956 and currently

operates under authority of Sections 5-401

through 5-408, Agriculture Article, Maryland

Annotated Code. Participation in the

program is voluntary and requires local

government and/or community funding. The

Department in 2011 entered into

Communities

Participating in

Mosquito Control

Services

Anne Arundel

Baltimore

Cecil

Charles

Dorchester County

Harford

Kent 

Queen Anne's

St. Mary's

Somerset

Talbot

Worcester

Other county lists will

be posted as they are

finalized.

Maryland.gov Phone Directory State Agencies Online Services

Enter search term

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Mosquito in

Maryland

Avoid Asian Tiger

Mosquito

Tips to Rid Your

Community of

Mosquito Breeding

Sites

Tips for Avoiding

Mosquito Bites

cooperative agreements with 16 counties

for mosquito control services and

conducted activities in 1,760 communities

with a total estimated population of

725,000 residents. The program employs

14 MDA classified positions, 3 long term

contractual positions and 60-70 seasonal

technicians. The administrative office, and

operation headquarters for Anne Arundel

County, is located in Annapolis. Regional

offices are located in College Park,

Hollywood, and Salisbury.

Mosquito control in Maryland is conducted

according to the concept of Integrated Pest

Management (IPM). IPM is based on

ecological, economic and social criteria

and integrates these multidisciplinary

methodologies to develop pest

management strategies that are practical

and effective to protect public health and

the environment and improve the quality of

life for Maryland residents and visitors. An

IPM program consists of surveillance for

larvae and adult mosquitoes; establishment

of action thresholds; and selection of

appropriate control strategies, using the

best available technology. A practitioner of

IPM must be knowledgeable of the biology

and ecology of mosquitoes, monitoring

techniques and best management

practices.

Mosquito Biology

Mosquitoes are members of the family

Culicidae in the order Diptera (true flies).

Adult mosquitoes are distinguished from

other flies by the presence of a long

proboscis and scales on the margins and

veins of the wing. Males differ from

females by having feathery antennae and

mouthparts not suited for piercing skin.

Mosquitoes are insects that develop

through four distinct life stages - egg, larva,

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pupa and adult. Only adult females feed on

blood which is a required source of protein

for egg development. Males and females

feed on plant nectar as a source of

carbohydrates.

There are three basic types of mosquito

eggs - those laid singly on the water

surface, each egg being buoyed by floats;

eggs laid on the water surface in groups or

rafts; and eggs laid singly out of the water

on a surface that will subsequently flood.

Mosquitoes which deposit eggs on the

water surface are commonly known as

permanent water breeders and include the

genera Anopheles,Coquillettidia, Culex and Culiseta.

Floodwater mosquitoes lay their eggs on a

moist substrate, out of the water, and

represent one of the most successful

reproductive strategies in the animal

kingdom. Female floodwater mosquitoes

are attracted by chemical stimuli to

oviposition sites and are not dependent on

water for oviposition, hence weather has

less impact on the reproductive success of

floodwater species than on permanent

water breeders. Floodwater mosquito

genera

include Aedes, Ochlerotatus and Psorophora.

All mosquito larvae are aquatic. The 60

species known to occur in Maryland have

adapted to a wide range of larval habitats,

including swamps, marshes, tree holes,

septic ditches, rock pools, etc. All of the

breeding sites have a common

characteristic of stagnant pools not subject

to significant wind or wave action or water

flow. Additionally, the breeding sites

generally have a low or non-existent

population of parasites or predators that

prey on mosquito larvae. Consequently,

flowing streams, tidal creeks, large ponds,

lakes and other large water bodies are not

typical mosquito breeding sites. Larvae

feed on microorganisms and particles of

organic matter. Mosquito larvae must have

access to atmospheric oxygen, which is

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obtained by means of a siphon tube that

penetrates the water surface or, in some

species, pierces the roots of aquatic

plants. The larval stage lasts from 4 to

several days and contains four separate

developmental periods termed instars.

The pupal stage is also aquatic but the

pupa can complete development on a moist

surface. It is during the pupal phase that

the transformation from an aquatic larva to

a terrestrial adult takes place. The pupal

stage lasts only a few days.

Adult female mosquitoes mate once during

their lifetime. This occurs shortly after

emergence from the pupal case. The blood

feeding habits of the female vary between

species. Some are general feeders while

others feed only on specific groups of

vertebrates such as birds or reptiles. The

flight habits are also variable, with some

species rarely flying more than several

hundred feet from their breeding sites and

others flying 20 miles or more.

Mosquito Surveillance

Modern pest management requires

surveillance data in order to plan and

evaluate control work. Field surveys are

the foundation of an effective program.

Data on the mosquitoes with the greatest

potential to adversely affect public health

and comfort, including data on mosquito

density and distribution, are essential in

order to plan and conduct effective control

measures. In Maryland, the species

occurring in the greatest abundance, or

that have the greatest impact on human

comfort, economic growth and public

health, are Ochlerotatus

sollicitans, Ochlerotatus

taeniorhynchus, Aedes albopictus, Aedes

vexans, Ochlerotatus

canadensis, Anopheles

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crucians/bradleyi, Anopheles

quadrimaculatus, Culex pipiens, Culex

salinarius,Coquillettidia

perturbans and Psorophora columbiae.

Several Aedes and Ochlerotatusspp.

and Coq. perturbans are implicated in the

transmission of eastern equine

encephalitis to humans, equines and

ratites. Dog heartworm in canines is the

most common mosquito-transmitted

disease in Maryland, with several vector

species.Culex species are important

vectors of West Nile encephalitis and St.

Louis encephalitis. Aedes albopictus,

popularly known as the Asian tiger

mosquito, is a recent introduction to the

Maryland mosquito fauna. It was

introduced into the United States from Asia

by the international used-tire trade and has

spread throughout much of the country via

interstate tire shipments. This species has

become a major pest in several urban

areas of Maryland and is a vector of West

Nile encephalitis. The newest addition to

the mosquito fauna of Maryland is Aedes

japonicus, first found in Frederick County

in 2000. Ae. japonicus is also a

beneficiary of the international tire trade

and an excellent vector of disease.

Larval surveillance requires extensive

logistical preparation due to the size and

remoteness of many breeding areas. The

largest expanse of breeding area exists in

the southern Eastern Shore region of

Maryland. In general, mosquito larval

habitat is most widespread in the coastal

plain. High-level aerial photography and

satellite imagery are used for rural areas to

locate potential breeding areas based on

soil and plant community associations. In

urban environments, Ae. albopictus and Cx.

pipiens are found in obscure breeding sites

in yard to yard searches.

Potential breeding areas are subject to

"ground truthing" to confirm the location of

the sites and measure the presence of

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mosquito larvae. Confirmed breeding areas

are mapped on United States Coast and

Geodetic topographic maps (scale

1:24,000), or larger scale city maps, and

used as a reference for future surveillance.

Frequent and regular inspections of

breeding areas are carried out from March

through September to determine larval

density and species composition. 

Larval surveillance data are used to guide

the course of the control program and are

the most important field data available to

the mosquito control manager. This

information is used in the decision-making

process of whether or not to initiate control

efforts, what type of control to employ and

in evaluating the effectiveness of the

control.

Breeding areas that consistently produce

large numbers of important pest or vector

species and are located within flight range

of a community are considered as potential

sites for control.

Several Aedes and Ochlerotatus spp. are

capable of long distance (up to 20 miles or

more) dispersal flights. Other species, such

as Ae. albopictus, Oc. canadensis,

and Coq. perturbans are weaker fliers (1-5

miles). Culexand Anopheles mosquitoes

have a much more restricted flight range

than do

mostAedes and Ochlerotatus mosquitoes

and breeding areas for the former species

more than two miles from a community are

not considered for control. All breeding

sites within a community, or close to the

perimeter of a community, are designated

as primary control sites for control of

mosquito larvae.

Meteorological conditions significantly

affect breeding sites. A prolonged drought

will evaporate the surface water from a

wetland and temporarily halt mosquito

larval production. However, a drought will

also eliminate the population of mosquito

predators and exacerbate mosquito

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breeding, particularly in areas producing

salt marsh Ochlerotatus species, when

surface water returns. A summer with

frequent rainfall and/or flooding tides will

maintain a higher water level, which usually

favors larval production

of Anopheles and Culex species, but may

also boost the population of predators and

eliminate mosquito production. Therefore, a

good larval surveillance program cannot be

static. It must be dynamic and flexible to

accommodate fluctuations in weather and

land use patterns.

Surveillance for adult mosquitoes is

conducted using traps and landing rate

counts. Traps are an easy, relatively low

cost way to obtain an index of the number

of mosquitoes in an area, but, data are

subject to wide variation. Trap data provide

a good historical record, if trap locations

are constant from year to year. Trap

collections are time-consuming to process

and the information on mosquito

abundance is often delayed for several

days after the catch is made and of

reduced value from the standpoint of

operational control. For arboviral

surveillance, traps utilize carbon dioxide as

an attractant to increase trap capture

rates..

In Maryland, a trap designed by the

Communicable Disease Center (CDC) is

the trap type generally used to monitor pest

and vector adult mosquitoes. The CDC trap

is battery-powered and easily portable. For

pest surveillance, the trap uses no source

of attraction other than a small light. A

collection of more than 10

anthropophagous (human biting) female

mosquitoes per night of trap operation is

considered to be the level which causes

discomfort and/or complaints from the

majority of people. The light trap action

threshold for ground spraying of adult

mosquitoes is 10 per trap night. The action

threshold to suppress pest populations of

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adult mosquitoes by aerial spraying

(application of insecticide by an aircraft) is

a light trap collection of 100 female

mosquitoes.

Landing rate counts provide immediate

indicators of adult mosquito activity. The

counts are taken for a short period of time

at specific, predetermined locations.

Inspectors serve as "bait" to attract

mosquitoes which attempt to blood feed. A

count is made of the number of mosquitoes

landing on the readily visible portions of the

inspectors' bodies, below the waist, during

a two minute interval. Landing rate counts

for salt marsh Ochlerotatus species

and Ae. albopictus can be taken during

daylight because these species will

actively attempt to blood feed at that time.

However, most other species,

particularly Anopheles spp.

and Culex spp., must be sampled during

twilight periods, or at night, because of

their nocturnal activity. The action

threshold for landing rate counts to justify

ground spraying for the control of adult

mosquitoes is 3 mosquitoes in 2 minutes.

The action threshold for aerial spraying is

12 mosquitoes per minute.

Mosquito-Borne Disease

Surveillance

The Maryland Department of Agriculture

(MDA) and the Maryland Department of

Health and Mental Hygiene (DHMH)

collaborate to conduct a surveillance

program to detect mosquito- borne viruses

of public health concern. The program

monitors the occurrence of eastern equine

encephalitis (EEE) virus, West Nile virus

(WNV), and St. Louis encephalitis (SLE)

and other viruses in mosquitoes, wild birds,

domestic animals and humans. These

viruses are maintained in nature in wild

bird-mosquito cycles. Isolation of viral

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presence in the bird-mosquito cycle

provides an early warning of virus

transmission and is cause for increasing

public awareness campaigns to reduce risk

of disease and to take proactive steps for

mosquito control to further reduce the risk

to humans, domestic animals and zoo

animals. 

West Nile virus has affected every region

of Maryland and is now considered as

being endemic throughout the state. During

the period 2001 to 2011 there were 215

human cases of disease caused by the

West Nile virus, including 20 fatalities.

Mosquito Control Options

The primary goal of the Mosquito Control

Section of MDA is to prevent the

occurrence of mosquito-borne disease in

humans and domestic animals. When

evidence of mosquito-borne disease is

detected, measures are taken to reduce

vector mosquito populations to as low a

level as practical. After the surveillance

and demographic data are analyzed and a

decision is made that control efforts are

justified, several options are available.

These range from complex to simple,

inexpensive to costly, and short-term to

long-term. What option to utilize is dictated

by the extent of the mosquito problem and

the available resources. 

Source Reduction Using Open Marsh

Water Management (OMWM) - OMWM is

a water management technique directed

toward the control of salt marsh

Ochlerotatus larval mosquitoes without

using pesticides. OMWM is an example of

applied ecology. It accomplishes control by

incorporating physical control (digging

ditches and ponds in the marsh) and

biological control (fish live in the ditches

and ponds and eat mosquito larvae). It is a

long lasting form of control and a system

that, when properly designed, has a life

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expectancy of 20 years or longer. Due to

this longevity, OMWM is the most

economical form of control, despite the

initial high investment. OMWM not only

provides excellent control of mosquitoes at

their source, it utilizes wildlife management

techniques to enhance the high salt marsh

habitat for a variety of game and non-game

species of fish and wildlife. The ponds

constructed for OMWM projects provide

habitat for submerged aquatic grasses, and

the ditches enhance the tidal marsh food

web while reducing nutrient flow into the

Chesapeake Bay.

Modern Maryland OMWM techniques are

designed to achieve long-lasting, effective

control of mosquito populations while

maintaining and often enhancing the

ecology of the tidal marsh environment.

These management techniques are

considered by many environmental

scientists to be acceptable alterations to

the tidal marsh habitat since they promote

the objectives of mosquito control

agencies, pesticide reduction advocacy

groups, and environmental protection

groups. Other environmental scientists

argue that no physical change of the tidal

marsh environment is acceptable. For

example, there is concern that OMWM

changes may adversely impact the black

rail, a species listed as in need of

conservation by the Natural Heritage

Program of the Maryland Department of

Natural Resources. Since 1991, OMWM

has been suspended in Maryland because

regulatory agencies have virtually stopped

the issue of necessary permits. Most

source reduction projects since 1991 have

been maintenance of previously managed

areas.

Biological Control - Larvivorous fish,

invertebrate predators, parasites and

diseases to control mosquitoes have been

widely used throughout the world. Almost

always, biological control agents are used

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against mosquito eggs, larvae and pupae.

Biological control of adult mosquitoes using

birds, bats, dragonflies and frogs has been

advocated, but supportive data are

anecdotal. There is no documented study

to show that bats, purple martins, or other

predators consume enough adult

mosquitoes to be effective control agents.

The Mosquito Control Section does not

advocate the establishment of bat boxes

by the public due to the increased risk of

human exposure to rabies.

The use of fish is particularly effective in

controlling the aquatic stages of the

mosquito. The Mosquito Control Program

maintains several rearing ponds throughout

Maryland to propagate Gambusia holbrooki

(mosquito fish) for distribution to

appropriate mosquito breeding sites. The

widespread use of larvivorous fish such as

Gambusia, a native fish to the Chesapeake

Bay and its tributaries, has been

discouraged by the Maryland Department

of Natural Resources due to concern the

fish may prey upon threatened or

endangered species of amphibians and

fish. As a consequence of this concern, the

biological control initiative using fish has

been reduced to stocking them only in

artificial wetlands, such as stormwater

retention ponds. 

Temporary Control- Control of mosquitoes

with the use of insecticides is commonly

referred to as temporary control because

the non-residual insecticides used in the

Maryland program provide only short-term

reduction of mosquito numbers. The

temporary control program is divided into

two categories - larviciding and

adulticiding. Insecticide applications are

made under the supervision of certified

pesticide applicators, pest control category

VIII, and regulated by State and federal

laws. Several certified applicators are

employed by the Mosquito Control Section.

No restricted use pesticides are applied in

Maryland for mosquito control by State or

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local government agencies.

Larviciding - Insecticide application

directed against larval mosquitoes is an

important component of an IPM mosquito

control program. Larviciding is the most

efficient type of temporary control. An

important part of the mission of the

Maryland Mosquito Control Program is to

prevent, or significantly reduce, adult

mosquito annoyance to humans, pets and

domestic livestock. It is more efficient to

eradicate or substantially diminish a brood

of mosquitoes while they are concentrated

as larvae in the aquatic habitat than to

control them as adults. For example, the

adult mosquitoes produced on one acre of

breeding area can disperse over 50,000

acres, assuming a flight range of five miles.

All larvicide applications are based on a

demonstrated presence of mosquito

larvae. Larval inspections are conducted

by trained personnel capable of identifying

instar stages of mosquitoes and

distinguishing among various genera.

Inspections for Aedes and Ochlerotatus

larvae must be conducted quickly after

heavy rains or flooding tides because,

during the summer, larvae can develop at a

rate of one instar per day. Therefore,

breeding sites must be located and treated

within five days after flooding. In most

instances, when widescale flooding has

occurred, only a small portion of the

breeding area can be inspected and a

determination made on the need for

treatment.

Larvicides are applied using manually

carried or vehicle-mounted spreading

equipment or from specially equipped

aircraft. Ground equipment application is

economical and has the advantage of

being able to specifically apply insecticides

to larval breeding sites only, as opposed to

aerial application where an entire area is

treated and much insecticide falls on dry

ground. However, aircraft are needed when

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large areas must be treated within the

short time available for treatment. Aircraft

are able to apply insecticide evenly over

large areas that would be difficult or

impossible to traverse on the ground.

All larvicide applications are made under

permits issued by the Maryland Department

of the Environment. Permit applications are

made on a county basis for specific areas

within the county and for individual

insecticides. The permit allows a limited

number of insecticide applications within a

specific time frame. The permit review

process is time consuming and often

prevents the timely application of mosquito

larvicides to new or previously

undocumented breeding sites.

The insecticides currently used for

larviciding in Maryland include Bacillus

thuringensis var. israelensis (B.t.i.), a

naturally produced bacterial toxin, and

methoprene (Altosid), a synthetically

produced insect growth regulator. B.t.i. is

one of the least toxic materials available

for larviciding and, when applied from the

ground, it is usually effective. It is the most

commonly used larvicide for ground

application. B.t.i. must be ingested by the

larvae in sufficient concentration to cause

death by disruption of the function of the

larval midgut. Due to the poor operational

results found in our quality control

evaluations, B.t.i. is seldom applied by

aircraft in Maryland. B.t.i. produces varying

levels of control depending on water

quality, amount of and type of vegetation

and species to be controlled. Under ideal

conditions, B.t.i. will control larvae for up to

24 hours.

Bacillus sphaericus is a relatively new

bacteria larvicidal product that is very

effective against Culex mosquitoes. It is

used in Maryland primarily to control Culex

salinarius and Culex pipiens. Bacillus

sphaericus can be effective

against Culexmosquitoes for up to 21

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days.

Two other bacterial products have recently

been registered as mosquito larvicides.

Both provide control over a wider range of

mosquito genera and habitat types than

B.t.i.. A product that combines B.t.i. and B.

shaericus to produce an additive toxic

effect controls multiple mosquito genera

where they occur in the same breeding

habitat. Sacchropolyspora spinose, the

most recently registered bacterial larvicide

product, appears to provide consistent

control over most mosquito genera and is

available in extended release formulations

that control larvae over long periods. Both

products are more expensive than B.t.i.

(approximately 5 times) and have limited,

special use in Maryland.

Methoprene is the most commonly used

larvicide for aerial application and is also

commonly applied by ground equipment.

This product provides 90-100% control of

emergence of adult floodwater mosquitoes.

There has been no observed negative

environmental impact as a result of the use

of methoprene for mosquito control in

Maryland to our knowledge. 

Larviciding is not allowed on certain State

parks, Federal refuges or Assateague

Island National Seashore. This is an

important factor impacting mosquito control

near these State and federal lands, which

serve as a source of adult mosquitoes to

the nearby residential areas. 

Criteria for Application of Larvicides

Populations of mosquito larvae are

sampled using a standard dipper which is

immersed and quickly withdrawn from

water. An assessment of the number of

larvae, instar stages and number of pupae,

is made. Field identification of mosquito

larvae is made to the genus level.

Wetlands are sampled to determine the

presence, spatial distribution and density

of a larval population. A decision to use a

larvicide to control a larval population takes

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into consideration the type of mosquito and

the distance to a residential area.

The physical nature of some larval habitats

makes standard larval dipping difficult;

samples may not be representative of the

actual larval populations. In sites such as,

but not limited to, dredged spoils

containments, wetlands with heavy

phragmites encroachment, cattail ponds,

stormwater management ponds and

containers, the use of larvicides is

warranted based on the observed

presence of larvae, historical treatment

records and/or adult mosquito surveillance

data. Wetlands and containers that lie in or

near residential sites will be treated on the

demonstrated presence of larvae.

A larvicide may be applied to a wetland for

the control of mosquito larvae when larvae

are present at a minimum average of one

larva per dip. Breeding habitats with a

minimum larval density of one per dip and

that lie within a two mile radius of an area

to be protected may be treated. The

breeding sites of Ae. vexans and Coq.

perturbans will be treated if they lie within a

five mile radius of an area to be protected.

For long distance flying salt marsh species,

Oc. sollicitans and Oc. taeniorhynchus,

breeding sites may be treated without

regard to distances to protection areas.

Adulticiding - Despite all efforts to prevent

adult mosquito populations from reaching

annoyance levels, it is inevitable that

outbreaks will occur. When this happens, it

is the mosquito control manager's

responsibility to reduce mosquito numbers

to a point below the action threshold to

protect public health and comfort.

Adulticiding is most effective when the

adult mosquito population is localized or

when spraying is carried out uniformly over

a large area to prevent reinfestation of

treated areas. Multiple spraying, spaced 2

to 3 days apart, may be necessary to

reduce the population of adult mosquitoes

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to a low level, particularly if mosquito-borne

disease transmission is possible.

Localized adult mosquito populations which

exceed the action threshold can be

managed with an application of insecticide

dispersed from truck-mounted, ultra low

volume (ULV), aerosol generators. The

principle insecticide applied for adult

mosquito control in Maryland is permethrin,

synergized with piperonyl butoxide (PBO).

ULV units disperse the synergized

pyrethroid insecticides (0.003 lb. active

ingredient per acre) over an effective

swath width of 300 feet. Applications

ideally are made when mosquito activity is

high, wind velocity is 2 to 10 mph, air

temperature is between 60 to 85 degrees

F, relative humidity is high and a

temperature inversion exists.

Aerial spraying for adult mosquito control

can be conducted when a large number of

mosquitoes, exceeding the aerial spray

action threshold, infest a community or

populated area of 500 acres, or more.

Spraying is conducted with a

Department-owned Beechcraft King-Air,

twin-engine, fixed-wing aircraft equipped

with an Ag-Nav global positioning system.

The principal insecticide used for aerial

adulticiding is naled (Trumpet EC) applied

at the rate of 0.8 to 1.2 fluid ounce per

acre (0.08 to 0.10 lb. a.i./acre). Aerial

spraying is conducted when weather

conditions favor high mosquito activity and

maximum retention of the spray particles

within the treatment area. Night vision

technology has enabled the aircraft to be

operated at night since 2005, resulting in a

higher degree of mosquito control. Due to

the high mosquito population needed for

justification (12 mosquitoes per minute

landing rate count and/or 100 mosquitoes

per light trap), most aerial spraying is

conducted in the southern Eastern Shore

region of Maryland.

Public Education - Mosquito control staff

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members meet with the press, attend

community meetings and communicate one

to one with residents to emphasize what

steps can be taken by individuals to reduce

mosquito problems. Cleanup of old tires,

buckets, cans and any other water holding

containers can significantly reduce

mosquito breeding sites in a community,

particularly in parts of the State with few

natural wetlands. Window screening will

keep mosquitoes outdoors. Pet owners are

urged to have their dogs protected against

dog heartworm disease, which is

transmitted by mosquitoes. Owners of

horses and other equine are urged to have

their animals vaccinated twice a year to

prevent occurrence of eastern equine

encephalitis. 

An initiative in 2000 and 2001 conducted

large scale mailing of information about Ae.

albopictus and its control. This information

was distributed in communities known to be

infested with Ae. albopictus and included

parts of Anne Arundel, Baltimore, Calvert

and Prince George's counties and

Baltimore City. Residents were urged to

conduct neighborhood cleanups to remove

containers used as mosquito breeding

sites. The evaluation of this effort has not

been able to demonstrate any appreciable

effect on reducing the mosquito breeding

containers in residential areas.

Traditionally, homes and commercial

developments were sited away from

wetlands and located in breezy, open

areas. However, during the past four

decades, there has been a shift in

development areas. Homes frequently are

built adjacent to, or in, wetland areas. This

occurs because of several possible

factors, including: (1) lack of, or greater

expense for, upland sites; (2) a desire to

live on or near waterfront property; (3)

diminished public concern about mosquito

bites or mosquito-transmitted disease; and

(4) reliance on government, private

contractors or self to alleviate problems

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associated with wetlands. In addition to

mosquitoes, residences near wetlands

frequently are impacted negatively by the

presence of deer flies, horse flies, stable

flies, biting midges ("no-see-ums"), black

flies and ticks.

The Mosquito Control Section receives

numerous service requests from residents

of communities in or near wetlands who

were unaware that their community was

prone to infestation by biting arthropods

prior to moving there. Planning and zoning

agencies could restrict development in

areas known to be potential sites of

arthropod-borne disease and nuisance. At

the very least, it should be an ethical

obligation of realtors to disclose to buyers

that living in or near some types of

wetlands will subject residents to greater

than normal exposure to insect and tick

bites. The Mosquito Control Section is

available to advise planning and zoning

agencies and realtors on known mosquito

producing wetlands. This public education

would reduce insecticide use by

government agencies, contractors and

homeowners, and have other ecological

benefits. 

Products Advertised for Mosquito Control -

There are numerous products being

advertised today alleging that they are

effective for mosquito control.

Unfortunately, these products have limited

or no value in reducing mosquito

annoyance. 

A mechanical trap (the Mosquito

Magnet(R)) is promoted as being capable

of "controlling" adult mosquitoes in an area

of up to 1 acre. This trap was evaluated by

MDA in 2001 and, while it was found to be

a good tool for collecting mosquito

specimens for surveillance purposes, the

claim of control could not be corroborated. 

Electronic devices that emit a high

frequency sound are advertised as being

effective to repel mosquitoes, as well as

other pests. These claims are false. The

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devices do not deter female mosquitoes

from attempting to bite, nor do they cause

mosquitoes to flee from the sound.

Electrocuting devices, popularly known as

"bug zappers", do not control mosquitoes.

Studies have shown that mosquitoes make

up less than one percent of the insects

killed by the zappers. Beneficial insects

such as beetles and moths make up the

bulk of the catch.

Plants such as the Citrosa plant are

claimed to have a mosquito-repelling

quality. The Citrosa plant is a genetically

engineered houseplant that incorporates

tissue cultures of the grass that produces

citronella oil into hybrid varieties of

geranium to produce a cultivar that emits a

citronella-like odor. Citronella oil does repel

mosquitoes, and it is a logical assumption

that the Citrosa plant's aroma would

produce similar results. However, the

citronella-like aroma of the Citrosa plant

does not repel mosquitoes. Mosquitoes

have been observed resting on the Citrosa

leaves. Crushing the Citrosa leaf and

rubbing it on the skin does not repel

mosquitoes. The idea of the Citrosa plant

was sound, but the results do not prove the

hypothesis that it is effective in repelling

mosquitoes.

Future Prospects and

Program Issues

Most people in Maryland are not willing to

accept large populations of nuisance

mosquitoes or the possibility of

mosquito-borne disease occurring in their

family. The demand for mosquito control as

a quality of life issue is likely to remain

strong in many areas. Strategies for future

control should ideally continue to diversify

to cope with insecticide resistance

management and changing societal

expectations. However, the diversity of

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control options continues to diminish as a

result of regulations and markets.

Creation of artificial wetlands in suburban

areas for stormwater management and

restoration of wetlands in agricultural fields

further complicate the issue by providing

new mosquito production areas. Best

management practices (BMP's) should be

established that incorporate mosquito

control concerns in the planning and

maintenance of these created wetland

habitats.

It will be a significant challenge to provide

a satisfactory mosquito control program in

the future. The most significant issue

impacting the Mosquito Control Program is

the increased difficulty of controlling

mosquitoes at the breeding site. Wetland

management, or source reduction, has

virtually ceased to be a significant program

component due to wetland protection

regulations and opposition by the Maryland

Department of Natural Resources and the

U.S. Fish and Wildlife Service. Larviciding

is effective, but costly, in terms of money

and labor and a comprehensive statewide

larvicide program is beyond the scope of

the current program resources. The

occurrence of new diseases (West Nile

virus) or the resurrection of old diseases

(malaria, yellow fever, etc.) are real threats

that may pose significant problems in the

future.

Last updated: Feb. 27, 2012

Contact Us Privacy Accessibility

50 Harry S. Truman Parkway, Annapolis, MD 21401

(410) 841-5700

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