SWS Wetland Concerns Committee Page 1 7/17/09 

Current Practices in Wetland Management for Mosquito Control 

I. ABSTRACT 

Mosquito-transmitted diseases raise public concerns about the relationships between 

wetlands and mosquitoes. We recommend that anyone working in wetlands gain a basic 

understanding of mosquito ecology so they can intelligently communicate with others on 

mosquito issues. 

Mosquitoes are a natural part of most types of wetlands, including those that are natural, 

restored, or degraded. Because wetlands provide many crucial environmental and 

socio-economic functions, services, and products, wetland protection needs to be at the 

forefront of strategies for dealing with mosquitoes, and we should continue to support 

and encourage efforts to restore wetlands. 

Changes to wetlands – either degradation or restoration – can change the likelihood that a 

given species of mosquito will use those wetlands as larval habitat. As a result, 

restoration may either increase or reduce the mosquito vectors of mosquito-borne 

diseases. Mosquito population responses to restoration depend upon the wetland 

processes that were degraded and the characteristics of processes restored. 

Where unacceptable mosquito production situations occur, environmentally compatible 

control methods to reduce mosquito production may be considered and employed, as 

long as other important wetlands values and functions are not unduly diminished. 

Control can be effectively practiced in managed wetlands where water is routinely 

controlled, constructed wetlands for wastewater treatment, or wetlands used for storm 

water retention. Some control measures may not be applicable or ecologically desirable 

in natural, unmanaged wetlands. The examples and practices described herein may 

require permits; the wetland practitioner should identify and comply with all laws 

applicable to their project area. 

Effective mosquito control requires interdisciplinary efforts (e.g., entomologists, wetland 

ecologists, hydrologists, restorationists) and an integrated pest management approach. 

No one mosquito-control strategy fits all situations, and mosquito management should be 

addressed on a case-by-case basis that identifies local and regional differences in 

mosquito species, geographic setting, and watershed context. The optimal approach 

requires mixing and matching strategies using the best available science. 

II. INTRODUCTION 

Wetlands are recognized for providing important ecosystem services such as wildlife 

habitat, floodwater control, water quality abatement and carbon sequestration. Wetlands 

are also recognized as natural sources of mosquitoes and are often included in 

management programs designed to reduce mosquito production from a wide variety of 

different sources. Wetland scientists are increasingly asked to address mosquito control 

and disease issues when dealing with wetland permitting, mitigation, and restoration. 

The Society of Wetland Scientists does not endorse the use of any specific management technique 

identified in this paper. Rather, the intent of the paper is to consider the wide range of options 

available to wetland scientists in addressing mosquito control. 
SWS Wetland Concerns Committee Page 2 7/17/09 

There has been substantial research on mosquito ecology, the role of wetlands and other 

habitats in disease transmission, and mosquito control methods. However, this 

information is not always readily available to wetland scientists working in the field and is 

often not directed at the question of how wetland restoration efforts influence mosquito 

populations and associated risks. 

Wetlands managers, regulators, and scientists must recognize and deal openly with the 

fact that wetlands produce mosquitoes. Willott (2004) gives an overview about wetlandassociated mosquito production problems and the need for all involved parties to address 

them responsibly. In areas with a history of mosquito production problems, organized 

mosquito control programs have existed for many years at state, county, or municipal 

levels. These programs can be a source of professional guidance and other assistance to 

parties who are creating new wetlands, restoring degraded wetlands, or acting as good 

stewards and managers of natural wetlands. In areas of the U.S. where mosquito control 

programs do not exist, or are only weakly funded or supported, the mosquito problems 

associated with wetlands are particularly challenging to manage. 

In the United States, responsibility for mosquito control lies within a hierarchy of local, 

state and federal agencies charged with addressing concerns ranging from threats to 

human health to pestilence issues that affect tourism, animal husbandry or the general 

comfort of the local human population. We do not review the scientific evidence for these 

societal concerns or make judgments about their validity. However, we recognize that 

wetland management for mosquito control may be at odds with management for other 

important goals such as maintaining biodiversity. 

For society to meet the mandate of ”no net loss” of wetlands through preservation, 

creation, and restoration, wetland professionals must address the public’s perception of 

mosquito production and vector-borne disease with an integrated approach that includes 

providing public education and outreach, soliciting public input from a wide range of 

stakeholders, and encouraging research on management techniques that achieve 

mosquito reduction goals while simultaneously maximizing the ecosystem services 

provided by wetlands. 

The goal of this SWS White Paper is to provide an overview of the context for present-day 

mosquito control and review some options available to wetland managers to reduce 

mosquito production in wetlands. The Society of Wetland Scientists does not endorse 

the use of any specific management technique identified in this paper. Rather, the intent 

of the paper is to consider the wide range of options that are currently available to 

wetland scientists charged with addressing mosquito control concerns. It is the goal of 

SWS to encourage ongoing research on management techniques and policies that 

continue to address societal concerns about mosquitoes and maintain robust wetland 

ecosystem services. 
SWS Wetland Concerns Committee Page 3 7/17/09 

III. MOSQUITO ECOLOGY 

Mosquito-transmitted diseases of potential concern to public health officials in North 

America are West Nile Virus, Eastern Equine Encephalitis, Western Equine Encephalitis, 

and La Crosse Encephalitis. The biology and ecology of mosquito species is highly 

relevant to the informed management of wetlands for such mosquito-transmitted 

diseases. For example, the primary habitat for specific species of Culex, the primary 

vector for West Nile Virus, changes across the United States. Storm water systems may 

be of concern in urban areas in most cities the US, while over-irrigated agricultural areas 

are a particular concern in the western US. 

The females of different mosquito species can be highly selective of oviposition sites 

according to environmental factors and hydrologic conditions. However, mosquitoes can 

be classified into two general groups based on their egg-laying and hatching behavior 

(Knight et al. 2003), namely the floodwater-ephemeral water habitat mosquitoes or the 

permanent-semipermanent aquatic habitat mosquitoes. Floodwater mosquito eggs are 

deposited on moist substrate and do not hatch until subsequently inundated. They 

include mosquitoes in the genera Aedes, Ochlerotatus, and Psorophora that are primarily 

daytime or crepuscular feeding mosquitoes. These mosquitoes can be significant vectors 

for diseases (Monath 1988). Floodwater mosquitoes are prevalent in sites receiving 

agricultural runoff and along wetland edges. Adults do not overwinter, but eggs laid in soil 

or in artificial containers do. 

Permanent or semipermanent aquatic habitat (includes standing water) mosquitoes lay 

eggs singly (Anopheles spp.) or in large rafts (Culex spp.) of 100 eggs or more on the 

water surface. These eggs hatch within a few days without an external hatching stimulus. 

IV. RISK ASSESSMENT 

Managers working in wetlands with significant nearby human occupancy may be 

required to address mosquito production without delay, and often rely on larval and 

adult mosquito surveillance and control responses provided by mosquito control 

programs. Risk assessment is the first step in developing a mosquito control strategy. 

Managers, regulators and the public must recognize that the mere presence of a 

wetland does not indicate the site is an important source of mosquitoes or mosquitotransmitted disease. Because wetlands are only one facet of mosquito-control, it is 

important to fully understand the extent to which responses that negatively affect 

wetland ecosystems will actually contribute to solving a given mosquito problem. People 

assessing risks should determine the answers to the following questions: 

a. How do local and regional wetlands fit into the overall mosquito or mosquito 

vector problem? 

b. When does a mosquito problem become severe enough to warrant interventions 

that impact wetlands? 

c. How will potential control strategies be tailored to address the problem while 

minimizing wetland impacts? 

d. Is there a phased or step-wise approach that can limit response to only that 
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required to control specific situations? 

e. Have alternatives been considered that minimize the loss of valued wetland 

services or avoid potentially converting wetlands from one type to another? 

Mosquito management plans generally include monitoring of mosquito populations and 

mosquito-transmitted diseases, and they define action levels based on anticipated health 

threats, nuisance concerns and other societal expectations. Mosquito control programs 

should follow an established Mosquito Management Plan that incorporates the principles 

of Integrated Pest Management. 

Mosquito monitoring or surveillance results should be used to determine the threat level 

identified in the mosquito management plan. Mosquito monitoring or surveillance is often 

carried out by professional mosquito control programs such as mosquito control districts, 

mosquito abatement districts, vector control districts, or county and state health 

departments. The objectives of such mosquito monitoring should be to establish both 

baseline and current data of mosquito species and abundance, map breeding and/or 

harboring habitats, estimate relative changes in population sizes, assess disease 

presence and nuisance levels. 

Management plans should include threat categories that represent a hierarchical scale of 

increasing risk to human or wildlife health based on local or regional disease activity, 

species-specific mosquito-vector population numbers, or simply overall mosquito 

population numbers. The plan should then include appropriate actions to take for each 

threat-level category. Perceived threats to human health, wildlife health, economic activity 

or human comfort vary temporally and spatially, so threats must be determined locally. 

Thresholds for treatment actions may be species specific for larval, pupal, and adult 

mosquito vectors and reflect the potential significance of a particular species or group of 

species in a particular health threat. For example, mosquito species known to be 

important in the transmission cycle of a disease in a particular geographic area, may have 

a lower action threshold than species with lesser transmission roles. It is also important to 

distinguish genuine disease-related health threats from public nuisance levels in 

considering control actions. In some cases, the same mosquito species may be linked to 

both health and nuisance concerns. In establishing categories, SWS encourages plans 

that weigh any negative impacts of actions on wetland ecosystems against the negative 

impacts of mosquitoes on humans and wildlife. 

 

V. MOSQUITO CONTROL STRATEGIES 

The control strategies discussed below recognize that some wetlands are more heavily 

managed than others, either by design or necessity. For the purposes of this paper, 

lightly managed wetlands are those that are intended to be natural or require minimal 

management. Heavily managed wetlands are those that require intensive human 

management, generally including active water-level manipulation. 

Many approaches and techniques are available to lessen mosquito production from 

wetlands, but the primary environmental, ecological, and regulatory reasons for wetland 
SWS Wetland Concerns Committee Page 5 7/17/09 

creation or restoration cannot be ignored when developing mosquito management plans. 

In some situations, a compromise between achieving all the desired wetland values and 

functions versus near-total suppression of mosquito production may be necessary (Collins 

and Resh 1989, Dale and Knight 2008). For constructed or restored wetlands, design 

features and management practices based on basin configurations, water-level 

management, mosquito predators, and vegetation management can help reduce 

mosquito production (Knight et al. 2003, Mayhew et al. 2004). If such steps fail to achieve 

satisfactory mosquito control, then additional biological or chemical controls might be 

needed, and may become the responsibility of local mosquito control programs or 

licensed mosquito control professionals. The extra expense incurred by mosquito control 

programs for contending with mosquito production from created or restored wetlands can 

be viewed as another cost of having or creating wetlands, an expense that may need to 

be planned for as an element of responsible wetland stewardship. 

The potential change in mosquito production as a result of restoring wetlands can be 

minimal, particularly when the proportion of restored wetlands is relatively small relative 

to the overall wetland resource area. Furthermore, if environmentally compatible 

mosquito-control, source-reduction measures are incorporated into a restoration 

project's location, design, construction, management, and maintenance, increases in 

mosquito production can be minimized. This will be most important where wetland 

restoration projects involve relatively large acreages in close proximity to human 

habitations and may help to avoid any increase in mosquito control measures. 

A) Techniques Suitable For Natural and Lightly Managed Wetlands

i. Passive approaches 

Passive techniques are useful when the wetland manager wishes to avoid ecological 

impacts to natural or restored wetlands that can result from control techniques. In such 

cases, managers may warn the public about presence of mosquitoes or restrict public 

access to the wetland rather than implement mosquito control. Such actions should 

always be based on surveillance data. In crafting messages to the public, the wetland 

practitioner must avoid creating a perception that wetlands are inherently mosquito 

“factories.” Rather, it should be stressed that while mosquitoes are produced in wetlands 

like other aquatic insects, in most cases their numbers do not reach public health concern 

or even nuisance levels. In some cases, a healthy, balanced ecosystem may retain 

enough predators of mosquito larvae to regulate mosquito population levels (Brodman et 

al. 2003). A passive strategy may not be acceptable in cases where there is a public 

health threat or the wetland produces more mosquitoes than the local human population 

can tolerate. 

 

ii. Biological control and mosquitocides

If passive approaches are not sufficient and additional control is needed, mosquito control 

agencies will generally implement an integrated pest management protocol that includes 

the introduction of mosquito larvae predators and the judicious use of insecticides (i.e. 

mosquitocides). Biological control is typically focused against the aquatic stages of the 

mosquito life cycle. At present, small, larvivorous fish are the only biological control agent 
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for larval mosquitoes that is practical and economically viable (Coykendall 1980, Swanson 

et al. 1996). There is no credible scientific evidence that any avian (Kale 1968) or bat 

species (Whitaker and Long 1998, Tuttle 2000) can effectively control adult mosquitoes. 

However, pond-breeding salamanders have been reported to regulate population levels 

of mosquito larvae and zooplankton (Brodman et al. 2003). 

The primary predator species used for biological control has been the mosquitofish 

(Gambusia spp., family Poeciliidae); however, the efficacy of alternative species continues 

to be evaluated (Cech and Moyle 1983, Bay 1985, Offill and Walton 1999, Walton 2007). 

Some of the controversies regarding the efficacy of Gambusia outside its native range are 

examined in Rupp (1996), Gratz et al. (1996) and Pyke (2008). One important issue is the 

risks to native ecosystems of introducing a non-native species. Questions that remain to 

be addressed include: (i) under what environmental conditions are the fish effective as 

biological control agents?, (ii) do the reductions in mosquito populations significantly 

reduce disease transmission to humans?, and (iii) do mosquitoes show compensatory 

responses to the reduced effects of larval stage density dependence? 

 

Although there are drawbacks to using non-native larvivorous fishes, there are settings 

where this approach can be ecologically-sound, practical and cost-effective, while 

avoiding or reducing the need for insecticide treatments (Sakolsky-Hoopes and Doane 

1998, Kent and Sakolsky-Hoopes 1999). The creation or restoration of aquatic habitat for 

native larvivorous fishes such as killfish in salt marshes, or certain species of minnows in 

freshwater wetlands, can substantially assist with mosquito control (Harrington and 

Harrington 1961, Nelson and Keenan 1992, Kent and Sakolsky-Hoopes 1999, Van Dam 

and Walton, 2007, Meredith and Lesser 2007). 

When passive and biological control methods are insufficient, current mosquito control 

programs prefer to use larvicides because control efforts are focused on the source of the 

problem and the area treated with larvicides is typically much smaller than with adulticides 

that are applied after adult mosquitoes have emerged and dispersed widely. The most 

commonly used larvicides are: 

 (1) Monomolecular films (MMF) to treat container-type habitats or other relatively small 

wetland areas MMFs spread across the water surface and suffocate immature 

mosquitoes. MMFs usually persist for a short period (~1-2 days), and some formulations 

are approved for use on potable water supplies., 

(2) Bacteria that produce mosquito toxins must be ingested by the larvae to be effective. 

Two types that are toxic to mosquitoes are naturally occurring bacilli -- Bacillus 

thuringiensis var. israelensis (Bti) (de Barjac) and B. sphaericus (Neide) -- and present 

minimal risks to humans and other non-target organisms at current application rates and 

by common modes of contact. They also degrade rapidly in the environment. 

 

(3) Insect growth regulators such as methoprene mimic insect hormones involved in 

molting. Immature mosquitoes exposed to sufficient dosages of methoprene do not molt 
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into adults. Methoprene also has very little (if any) effect on non-target wetland organisms 

when used in mosquito control formulations (Schmude et al. 1998, Balcer et al. 1999). 

(4) The organophosphate temephos is a chemical insecticide that for some mosquito 

control programs provides the only affordable, practical, and effective larvicide for treating 

large geographic areas. It can also be an alternative control product for mosquito species 

or in habitats where Bti or methoprene do not give efficacious control. 

If larvicides cannot be used or prove ineffective, it might be necessary to resort to the use 

of adulticide. This method usually involves more widespread applications of the 

insecticides, often directly over or within where people live, work, or recreate. The most 

commonly used adulticides include organophosphates (e.g., malathion, naled) and 

synthetic pyrethroids (e.g., permethrin, resmethrin, sumithrin). 

The U.S. Environmental Protection Agency registers mosquitocides (for larvae or adults) 

that it determines do not pose unreasonable risks to human health, wildlife, or the 

environment. Information about how the EPA registers and authorizes the use of 

mosquitocides, and the agency's perspectives about the risks of mosquitocide use to 

humans, wildlife, or the environment, are contained in the “Mosquito Control Fact Sheets” 

available at http://www.epa.gov/pesticides/factsheets/health_fs.htm. 

The choice of the mosquitocide to use is a complex decision involving many variables, 

including types of mosquito species to be controlled, life stages involved, types and 

extents of habitats to be treated, the presence of non-target species of special concern, 

and other environmental impacts. 

iii. Water-level management

The flow of water through a wetland and its related volumetric turnover rate influence 

mosquito production, but flow rates detrimental to immature mosquito survival are too high 

to be practical for effective mosquito control in most types of wetlands. Managing 

wetlands for adequate water turnover rates enhances mosquito control by helping to 

eliminate the accumulation of stagnant, organically-rich waters that attract certain 

standing-water mosquitoes such as Culex spp. Flowing water also maintains high oxygen 

levels, which contributes to reducing toxic metabolites. These factors enhance the survival 

of the aquatic predators of mosquito-larvae. In many Midwestern wetlands, such as fens, 

sedge meadows, dolomite prairies, etc., groundwater contributions from seeps, springs, 

and upwellings can provide this slow flushing, as well as maintain colder water 

temperatures not suitable for many mosquito species. Water levels management is also 

used as an indirect means to manipulate the presence and biomass of vegetation (see Biii below). 

B) Techniques Suitable for Heavily Managed Wetlands

Mosquito control techniques are applied somewhat differently than described above in 

wetlands that are intended to be heavily managed. The discussion below assumes that 
SWS Wetland Concerns Committee Page 8 7/17/09 

mosquito control, as opposed to maintaining of enhancing other wetland functions and 

services, is the primary goal of wetland management in such cases. 

i. Basin Design And Topographic Configurations

Natural and lightly managed wetlands should generally not be subjected to changes in 

topography for the sole purpose of mosquito control, with the possible exception of 

restoring predator balance in a degraded wetland. However, in heavily managed wetland 

systems where mosquito reduction is the primary goal, there are topographic design 

considerations that may be applied to minimize mosquito production and the need to 

apply pesticides. 

Wetlands that lack deep water zones (water depth > 1.5 m) and vigorous populations of 

mosquito predators are more prone to mosquito production problems than those that 

contain permanent deep water zones. Although having deep water zones will not always 

prevent high levels of mosquito production from occurring, deep water areas provide 

habitat for important predators of mosquitoes such as larvivorous fishes, predaceous 

aquatic insects, and salamander larvae. 

Wetlands that have gently sloping margins or edges (e.g., a vertical:horizontal slope of 

<1:10) tend to develop dense emergent vegetation in shallow areas. The physical 

structure of emergent vegetation provides several important wetland functions (Mitsch and 

Gosselink 2000, Kadlec and Wallace 2009) and is frequently a goal in wetland mitigation 

or restoration. However, dense vegetation can also create refugia where mosquito larvae 

hatch and survive to emergence as adults. In less disturbed systems, this increase in 

mosquito production may be offset with predation; however, more disturbed wetlands may 

not provide for this control. Steeper side slopes (e.g., >1:4) are less prone to develop 

dense vegetative cover across extensive areas of a wetland. Unfortunately, such slopes 

may be more susceptible to soil erosion. Regardless of the slope angle, if the intent of the 

slope angle is primarily to control mosquito production, the sides should uniformly and 

continuously taper downward from shallow edges towards a deeper central water body to 

prevent isolated pockets of standing water along a wetland’s margins during drawdown or 

droughts, as well as after rainfall events that do not completely fill the wetland basin 

(Mulhern 1980, Knight et al. 2003). 

ii. Water-Level Management

Design features and operations that move water through wetlands are critical to managing 

mosquitoes; however, prior to selecting this management technique, a wetland scientist 

must examine the type and functions of the wetland in question. Numerous wetland types 

are not suitable candidates for significant water-level management. 

In addition to the goal maintaining a permanent pool of water (see B-iii below), the 

margins of wetlands should not undergo extensive wet-dry-wet cycles that can lead to 

production of floodwater mosquitoes from peripheral micro-habitats that lack mosquito 

predators. When a wetland dries out (e.g., as in seasonal wetlands or vernal pools), 

many aquatic predators of mosquito larvae perish, while floodwater mosquitoes can 

survive as eggs that remain viable in moist mud or desiccated bottoms and then hatch 
SWS Wetland Concerns Committee Page 9 7/17/09 

soon after water is again present. The floodwater mosquitoes (Aedes, Ochlerotatus, and 

Psorophora spp.) produced from such temporary waters can transmit the causative 

agents of serious diseases and are capable of long-distance flights. When a wetland has 

permanent water cover, along with open channels or paths through thick vegetation for 

aquatic predators of mosquito-larvae to move around, the production of standing-water 

mosquitoes (e.g., Culex spp.) is lessened. Deeper water also reduces production of 

mosquito larvae that attach to the roots of emergent plants (e.g. Coquilletidia perturbans). 

iii. Vegetation Management

Dense emergent or floating vegetation cover creates refugia for mosquitoes from their 

predators. The primary goal of vegetation management is to create open water areas that 

present unfavorable conditions for immature mosquito development and for adult 

mosquito resting. Open water areas enhance the negative effects of wind on mosquito 

activity, deter oviposition, reduce immature mosquito survival by increasing predation and 

drowning by waves, and lower the accumulation of organic debris in a wetland system. 

Management involving selective plant removal, limited controlled burning, or minimal 

applications of herbicide may be necessary when water depth manipulation cannot 

adequately prevent the excessive growth of emergent plants. Limited mowing, disking, 

and grazing are also used to alter plant species composition and abundance in order to 

enhance use by certain species of wildlife (Payne 1992, Kwasny et al. 2004). 

In most instances, routine vegetation management can significantly reduce mosquito 

production, but if done incorrectly, it can greatly enhance mosquito production. For 

example, razing macrophytes or inundating dried plant biomass for vegetation control 

purposes may significantly increase mosquito production. Incorporating design features 

such as raised planting beds and deep water zones that limit the proliferation of emergent 

macrophytes (Thullen et al. 2002) provide more effective mosquito control than does 

repeated vegetation removal. 

Although vegetation suppression is effective for mosquito control, it is generally not 

favorable for important wetland functions and services such as wildlife habitat or water 

quality improvement. Many wetland functions emerge directly from the diversity and 

primary productivity of the plant community. In addition, disturbances such as mowing, 

disking and grazing may introduce opportunities for invasive species. Some level of 

compromise in vegetation cover management may be required, depending on the balance 

between the desires for maintaining wetland functions and avoiding increased mosquito 

production. 

iv. Source Reduction

Source reduction refers to techniques that are generally, but not always, non-chemical 

and designed to limit mosquito production at oviposition sites or larval-rearing sites. 

Because source reduction typically involves habitat modification, the strategy is generally 

used as a final recourse to reduce mosquito production or as an alternative to reduce 

insecticide use. The range of effects that source reduction approaches have on wetland 

functions has not been fully assessed, but individual techniques present problems in a 
SWS Wetland Concerns Committee Page 10 7/17/09 

variety of situations. The use of source reduction techniques in natural wetlands requires 

careful consideration by stakeholders because of the inevitable tradeoffs between the 

benefits for mosquito control and reduced pesticide use, and the adverse effects of habitat 

alteration on wetland ecosystem function. For this reason, we consider source reduction 

appropriate primarily for wetland ecosystems that are heavily managed. 

Source reduction approaches in mosquito-control integrated pest management programs 

are usually preferable to the use of insecticides, provided that the source reduction can be 

practicably and effectively applied and it does not cause unintended or unacceptable 

environmental impacts. The type and extent of source reduction that is possible in a given 

wetland depends upon how much water-management capability exists for managing 

water flows or wetland water levels. More sophisticated source reduction can be achieved 

in a coastal impoundment with an automated vertical lift than one with a simple riser-board 

structure. The automated vertical lift allows fine-tuned dynamic management of tidal 

exchanges and marsh water levels. Similarly, more can be achieved in a stormwater 

retention pond with an adjustable riser-board outlet versus a fixed-crest weir outlet. For 

many natural wetlands, especially groundwater-fed wetlands with saturated soils for a 

significant portion of the growing season, this technique is not appropriate or even 

possible without destroying the wetland or converting it to a completely different wetland 

type. 

Source reduction in wetlands customarily encompasses three broad categories of control 

measures: (1) basin/topography design configurations, (2) water-level management, and 

(3) vegetation management. These measures are most applicable wetlands that were 

constructed or developed for specific purposes, often focusing on a single wetland 

function, while often providing other wetland functions. Managed wetlands include 

wildlife refuges in which water control is routinely practiced, wetlands constructed for 

wastewater treatment, and wetlands constructed for or used as stormwater retention 

facilities, although there are many other wetland types that may fall under this category 

(e.g., wetlands created on golf courses). The source reduction measures specified may 

or may not be applicable to natural or less managed wetlands. 

There is a large literature on best management practices (BMPs) for achieving source 

reduction in wetlands, only a few of which we cite here. While the reports are often written 

for a particular geographic region, similar approaches are applicable across regions. 

Besides offering prescriptions for applying source reduction techniques to control 

mosquito production in wetlands, some of the works cited below also contain citations of 

studies and surveys that have documented the types and extent of mosquito production 

found in natural wetlands, stormwater management basins, wetlands mitigation projects, 

waterfowl impoundments, and other kinds of wetlands. 

Analyses, recommendations or BMPs that address mosquito production in wetlands have 

been published for New Jersey (Shisler and Charette 1986, NJDEP 2004), Maryland 

(Dorothy and Staker 1990, Bradley and Kutz 2005), Florida (O’Meara 1997, University of 

Florida 1998), California (Metzger 2004, Walton 2003), and coastal wetlands (Brockmeyer 

et al. 1997). California published a set of BMPs for mosquito control in seasonal, semi-
SWS Wetland Concerns Committee Page 11 7/17/09 

permanent, and permanent wetlands managed for waterfowl and other birds (Kwasny et 

al. 2004). Finally, the EPA recently released a new nationwide set of BMPs for stormwater 

retention ponds and their associated wetlands (see the agency’s Stormwater Wet Pond 

and Wetland Management Guidebook). EPA has incorporated these mosquito control 

measures in the siting, design, construction and management of such facilities (EPA, 

2009). 

The source-reduction technique known as “open marsh water management” (OMWM) is a 

selective ponding-and-ditching technique designed to encourage predation of mosquito –

larvae by native fishes in tidal wetlands. The technique is described by Meredith et al. 

(1985) for Delaware, with other states such as Massachusetts, New Jersey, Maryland, 

and Florida having their own OMWM guidelines. OMWM alters the wetland topography 

and hydrology to achieve mosquito reduction. Although the goal is to minimize changes in 

wetland structure and function, OMWM can effectively alter the functional type of a 

wetland. For this reason and others, this is not a technique applicable to all locations or 

one that would be accepted in all locales. “Runnelling” is a modification of OMWM 

(Hulsman et al. 1989) that may be used in tidal marshes with acid sulphate soils. 

Runnelling involves the selective excavation of shallow channels that provide tidal 

circulation and larvivorous fish access to mosquito-breeding depressions. OMWM and its 

impacts are reviewed by Wolfe (1996) and the long-term impacts of runnelling are 

described by Dale (2005). 

 

It should be noted that the old parallel-grid-ditching method of source reduction for salt 

marsh mosquito control, which involved non-selective excavation of open tidal ditches 

geometrically placed over vast acreages, was generally ineffective in controlling 

mosquitoes, had significant negative impacts on coastal marshes, including substrate 

disturbances that led to the introduction of invasive species (e.g., Phragmites), drying of 

marsh surfaces that led to increased oxidation and loss of marsh substrate, and changes 

in plant communities (e.g. establishment of shrubs) and wildlife habitat values The 

technique of OMWM, when properly employed, avoids almost all of these past adverse 

impacts. In fact, in previously parallel-grid-ditched marshes, the installation of OMWM 

systems is often viewed as a habitat-restoration technique by restoring standing water to 

marsh surfaces that have been dewatered by the parallel-grid-ditches (Meredith et al 

1985). 

VI. SUMMARY 

Wetlands are fragile systems that nevertheless provide many crucial environmental and 

socio-economic functions, services, and products As society is confronted with new and 

emerging mosquito-borne diseases, the need to simultaneously protect human health and 

wetland functions will only increase. If society wishes to sustain the mandate of ”no net 

loss” of wetlands through preservation, creation, or restoration of these valuable 

ecosystems, then wetland professionals must address the public perception of mosquito 

production and vector-borne disease with an integrated approach that includes providing 

public education and outreach while soliciting public input. Additionally, society must 
SWS Wetland Concerns Committee Page 12 7/17/09 

confront development that significantly degrades wetlands, juxtaposing humans with 

unstable biological systems. 

Wetland professionals, regulatory agencies, public health organizations, and mosquito 

control agencies should consult with one another and the public during the planning, 

design, implementation, management and maintenance phases of wetland creation, 

restoration or enhancement projects. One price of creating and restoring wetlands may be 

the need to monitor for mosquito production. Criteria for the long-term success of wetland 

creation or restoration projects must include the minimization of mosquito production to 

the extent practicable, done in an environmentally-compatible manner consistent with the 

achievement of other objectives specified for a particular project (Willott 2004). 

Mosquito species have evolved to exploit a wide variety of habitats. Because mosquitoes 

are a natural part of wetland ecosystems, permanent and total elimination of mosquitoes 

from wetlands is not a realistic or achievable goal. However, current scientific 

understanding supports the position that we can take environmentally-compatible 

measures to help minimize mosquito production from natural, created, or restored 

wetlands, and especially from many types of degraded wetlands. The SWS advocates 

science-based use of system design concepts that encourage ecological diversity and 

natural mosquito predators in all wetland types, minimizing to the extent practicable the 

creation or perpetuation of site features that promote mosquito production in the first 

place. 
SWS Wetland Concerns Committee Page 13 7/17/09 

LITERATURE CITED: 

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SWS Wetland Concerns Committee Page 18 7/17/09 

ABBREVIATIONS 

Bti Bacillus thuringiensis var. israelensis 

BMPs best management practices 

EPA U.S. Environmental Protection Agency 

MMF monomolecular films 

NJDEP New Jersey Department of Environmental Protection 

OMWM open marsh water management 

SWS Society of Wetland Scientists 

WNV West Nile virus 
SWS Wetland Concerns Committee Page 19 7/17/09 

This is a contribution from the Wetland Concerns Committee of the Society of Wetland 

Scientists. It was edited by J. Patrick Megonigal and written by the following authors (in 

alphabetical order): 

Joe Berg, PWS, CSE 

Mark Felton, PWS 

Leslie Gecy, PWS 

Aimlee Laderman, Ph.D. 

Catherine Mayhew 

Jeff Mengler 

William H. Meredith, PhD, PWS 

Nancy Read, Ph.D. 

Jorge Rey, Ph.D. 

Gabrielle Sakolsky-Hoopes 

William E. Walton, Ph.D. 

Roger Wolfe, PWS