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, in cluding those that are natural, restored, or degraded. Becaus e wetlands provide many crucial environmental and

socio-economic functions, services, and products, we tland protection needs to be at the forefront of strategies for dealing with mo squitoes, and we should continue to support and encourage efforts to restore wetlands.

Changes to wetlands – either degradation or re storation – can change the likelihood that a given species of mosquito will use those we tlands as larval habitat. As a result, restoration may either incr ease or reduce the mosquito vectors of mosquito-borne diseases. Mosquito population respons es to restoration depend upon the wetland processes that were degraded and the char acteristics of processes restored.

Where unacceptable mosquito production situat ions occur, environmentally compatible control methods to reduce mosquito pr oduction 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 wastew ater treatment, or wetlands used for storm

water retention. Some control measures ma y not be applicable or ecologically desirable in natural, unmanaged wetlands. The exampl es 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 interdi sciplinary efforts (e.g., entomologists, wetland ecologists, hydrologists, restorationists) and an int egrated pest management approach. No one mosquito-control strategy fits all situations, and mosquito management should be addressed on a case-by-case basis that i dentifies local and regional differences in mosquito species, geographic setting, and wa tershed context. The optimal approach requires mixing and matching strategies using the best available science.

II. INTRODUCTION

Wetlands are recognized for providing import ant 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 mosqui to production from a wide variety of

different sources. Wetland scientists are incr easingly 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 t he 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 res earch on mosquito ecology, the role of wetlands and other habitats in disease transmission, and mosqui to control methods. However, this information is not always readily available to wetland scientists working in the field and is often not directed at the ques tion 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. W illott (2004) gives an overview about wetlandassociated mosquito production problems and t he 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 m any 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, re storing degraded wetlands, or acting as good stewards and managers of natural wetlands. In areas of t he U.S. where mosquito control programs do not exist, or are only weakly funded or support ed, 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 char ged with addressing concerns ranging from threats to human health to pestilence issues that affe ct 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. Ho wever, 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 restorati on, wetland professionals must addr ess the public’s perception of mosquito production and vector-borne disease with an integrated approac h 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 provi de an overview of the c ontext for present-day mosquito control and review some options available to wetland managers to reduce mosquito production in wetl ands. The Society of Wetland Scientists does not endorse the use of any specific managem ent technique identified in th is paper. Rather, the intent of the paper is to consider the wide range of options that are cu rrently available to wetland scientists charged with addressing mosqui to control concerns. It is the goal of SWS to encourage ongoing research on managem ent 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 Equi ne Encephalitis, Western Equine Encephalitis, and La Crosse Encephalitis. The biology and ec ology of mosquito species is highly relevant to the informed management of wetlands for such mosquito-transmitted diseases. For example, the primar y 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 hydrol ogic conditions. However, mosquitoes can be classified into two general groups bas ed on their egg-laying and hatching behavior (Knight et al. 2003), namely t he floodwater-ephemeral water habitat mosquitoes or the permanent-semipermanent aquatic habitat mosqui toes. Floodwater mosquito eggs are deposited on moist substrate and do not hat ch until subsequently inundated. They include mosquitoes in the genera Aedes

, Ochlerotatus , and Psorophora that are primarily daytime or crepuscular feeding mosquitoes. T hese mosquitoes can be significant vectors for diseases (Monath 1988). Floodwater mosqui toes 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 (i ncludes 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 fe w 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 wit hout 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 re cognize that the mere presence of a wetland does not indicate the site is an impor tant source of mosquitoes or mosquitotransmitted disease. Because wetlands are onl y one facet of mosquito-control, it is important to fully understand t he 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 in to 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 thatSWS Wetland Concerns Committee Page 4 7/17/09 required to control specific situations?

e. Have alternatives been considered t hat minimize the loss of valued wetland services or avoid potentially conver ting wetlands from one type to another?

Mosquito management plans generally include monitoring of mosquito populations and mosquito-transmitted diseases, and they defi ne action levels based on anticipated health threats, nuisance concerns and other societal expectations. Mosquito control programs should follow an established Mosquito Management Plan that incorporat es the principles of Integrated Pest Management.

Mosquito monitoring or surveillance results should be used to determine the threat level identified in the mosquito m anagement plan. Mosquito monitoring or surveillance is often carried out by professional mosquito control pr ograms such as mosquito control districts, mosquito abatement districts, vector cont rol districts, or c ounty 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 c hanges in population sizes, assess disease presence and nuisance levels.

Management plans should include threat categories that represent a hier archical scale of increasing risk to human or wild life health based on local or regional disease activity, species-specific mosquito-vector populati on numbers, or simply overall mosquito population numbers. The plan should then incl ude 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 t he potential significance of a par ticular species or group of species in a particular health threat. Fo r 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 th reats 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 est ablishing 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 recogni ze 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 availabl e to lessen mosquito production from wetlands, but the primary environmental, ecol ogical, and regulatory reasons for wetlandSWS Wetland Concerns Committee Page 5 7/17/09 creation or restoration c annot 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 c onstructed or restored wetlands, design features and management prac tices based on basin configurations, water-level management, mosquito predators, and v egetation 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 producti on 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 rest ored wetlands is relatively small relative

to the overall wetland resource area. Fu rthermore, 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. Th is 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 pres ence of mosquitoes or restrict public access to the wetland rather than implement mosquito control. Such actions should always be based on surveillance data. In cr afting messages to the public, the wetland practitioner must avoid creat ing 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 t heir numbers do not reach public health concern or even nuisance levels. In some cases, a healthy, balanced ecosystem may retain enough predators of mosquito larv ae to regulate mosquito population levels (Brodman et al. 2003). A passive strategy may not be acc eptable in cases where there is a public health threat or the wetland produces more mosquitoes than t he local human population

can tolerate.

ii. Biological control and mosquitocides If passive approaches are not sufficient and addi tional control is needed, mosquito control agencies will generally implement an integrated pest management protocol that includes the introduction of mosquito la rvae 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, larviv orous fish are the only biological control agentSWS Wetland Concerns Committee Page 6 7/17/09 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) c an 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 specie s used for biological control has been the mosquitofish ( Gambusia spp., family Poeciliidae); however, the e fficacy of alternative species continues to be evaluated (Cech and Moyle 1983, Ba y 1985, Offill and Walton 1999, Walton 2007).

Some of the controversie s 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-nat ive 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 mosqui to 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-nativ e larvivorous fishes, there are settings where this approach can be ecologically-sound, practical and cost-effective, while avoiding or reducing the need for insect icide treatments (Sakolsky-Hoopes and Doane 1998, Kent and Sakolsky-Hoopes 1999). The creati on or restoration of aquatic habitat for

native larvivorous fishes such as killfish in sa lt marshes, or certain species of minnows in freshwater wetlands, can substantially a ssist 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 ar e insufficient, current mosquito control programs prefer to use larvici des because control efforts are focused on the source of the problem and the area treated with la rvicides is typically much smaller than with adulticides that are applied after adult mosquitoes hav e emerged and dispersed widely. The most commonly used larvicides are:

(1) Monomolecular films (MMF) to treat contai ner-type habitats or other relatively small wetland areas MMFs spread across the water surface and suffocate immature mosquitoes. MMFs usually persist for a shor t 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 mosqui toes 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 al so degrade rapidly in the environment.

(3) Insect growth regulators such as me thoprene mimic insect hormones involved in molting. Immature mosquitoes exposed to sufficient dosages of methoprene do not moltSWS Wetland Concerns Committee Page 7 7/17/09 into adults. Methoprene also has very little (if any) effect on non-target wetland organisms when used in mosquito control formulations (S chmude 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 alter native 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 invo lves more widespread applications of the insecticides, often directly over or within where people live, work, or recreate. The most commonly used adulticides include organophosphat es (e.g., malathion, naled) and synthetic pyrethroids (e.g., perme thrin, resmethrin, sumithrin).

The U.S. Environmental Protection Agency registers mosquitocides (for larvae or adults) that it determines do not pose unreasonabl e 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 “Mo squito 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 treat ed, 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 re lated volumetric turnover rate influence mosquito production, but flow rates detrimental to immature mosquito survival are too high to be practical for effective mosquito c ontrol in most types of wetlands. Managing wetlands for adequate water turnover rates enhanc es mosquito control by helping to eliminate the accumulation of stagnant, organi cally-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., groundw ater contributions from seeps, springs, and upwellings can provide this slow flushi ng, 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 t he presence and biomass of vegetation (see Biii below).

B) Techniques Suitable for Heavily Managed Wetlands

Mosquito control techniques are applied some what differently t han described above in wetlands that are intended to be heavily m anaged. The discussion below assumes thatSWS Wetland Concerns Committee Page 8 7/17/09 mosquito control, as opposed to maintain ing 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 gener ally 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. Howeve r, in heavily managed wetland systems where mosquito reduction is the primary goal, there are topographic design considerations that may be applied to mi nimize 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 mos quito production problems than those that contain permanent deep water zones. Although having deep water zones will not always prevent high levels of mosquito producti on 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 vegetati on provides several important wetland functions (Mitsch and Gosselink 2000, Kadlec and Wallace 2009) and is frequently a goal in wetland mitigation or restoration. However, dens e vegetation can also create re fugia where mosquito larvae hatch and survive to emergence as adults. In less disturbed systems, this increase in mosquito production may be offset with predat ion; 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 mosqui to 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 t hat do not completely fill the wetland basin (Mulhern 1980, Knight et al. 2003).

ii. Water-Level Management Design features and operations t hat move water through wetlands are critical to managing mosquitoes; however, prior to selecting th is management technique, a wetland scientist must examine the type and func tions of the wetland in question. Numerous wetland types are not suitable candidates for significant water-level management.

In addition to the goal maintaining a perm anent pool of water (see B-iii below), the margins of wetlands should not undergo extensive wet-dry-we t cycles that can lead to production of floodwater mosquitoes from per ipheral micro-habitats that lack mosquito predators. When a wetl and dries out (e.g., as in seasonal wetlands or vernal pools), many aquatic predators of mos quito larvae perish, while floodwater mosquitoes can survive as eggs that remain viable in mo ist mud or desiccated bottoms and then hatchSWS Wetland Concerns Committee Page 9 7/17/09 soon after water is again presen t. 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 mo ve around, the producti on 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 veget ation 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 accumula tion of organic debris in a wetland system.

Management involving selective plant remova l, limited controlled burning, or minimal applications of herbicide may be necessa ry 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 m anagement can significantly reduce mosquito production, but if done incorre ctly, it can greatly enhance mosquito production. For example, razing macrophytes or inundating dr ied plant biomass for vegetation control purposes may significantly increase mosquito production. Incorporat ing design features such as raised planting beds and deep water zones that limit the prolif eration of emergent macrophytes (Thullen et al. 2002) provide more effective mosquito control than does repeated vegetation removal.

Although vegetation suppression is effective fo r mosquito control, it is generally not favorable for important wetland functions and services such as wildlife habitat or water quality improvement. Many we tland functions emerge direct ly from the diversity and primary productivity of the pl ant community. In addition, disturbances such as mowing, disking and grazing may introduce opportunities for invasive species. Some level of compromise in vegetation cover managem ent 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 ov iposition sites or larval-rearing sites. Because source reduction typically involves habi tat 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 t hat source reduction approaches have on wetland functions has not been fully assessed, but i ndividual techniques present problems in aSWS Wetland Concerns Committee Page 10 7/17/09 variety of situations. The use of source r eduction techniques in natural wetlands requires careful consideration by stakeholders becaus e of the inevitable tradeoffs between the benefits for mosquito control and reduced pestici de use, and the adverse effects of habitat alteration on wetland ecosystem function. For th is reason, we consider source reduction appropriate primarily for wetland ec osystems that are heavily managed.

Source reduction approaches in mosquito-c ontrol integrated pes t management programs are usually preferable to the us e of insecticides, provided t hat the source reduction can be practicably and effectively applied and it does not cause unintended or unacceptable environmental impacts. The type and extent of s ource reduction that is possible in a given wetland depends upon how much water-managem ent 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 vert ical 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 fi xed-crest weir outlet. For many natural wetlands, espec ially 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 conver ting it to a completely different wetland type.

Source reduction in wetlands customarily enc ompasses three broad categories of control measures: (1) basin/topography design confi gurations, (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 construct ed for or used as stormwater retention facilities, although there are m any 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 liter ature on best management practices (BMPs) for achieving source reduction in wetlands, only a few of which we ci te here. While the repor ts are often written for a particular geographic region, simila r approaches are applicable across regions. Besides offering prescriptions for applying source reduction techniques to control mosquito production in wetlands, some of the wo rks cited below also contain citations of studies and surveys that hav e documented the types and ext ent of mosquito production found in natural wetlands, stormwater managem ent 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, Bradl ey and Kutz 2005), Florida (O ’Meara 1997, University of Florida 1998), California (Metzger 2004, Walt on 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 wa terfowl and other birds (Kwasny et al. 2004). Finally, the EPA recently released a new nationwide set of BMPs for stormwater retention ponds and their associ ated wetlands (see the agency’s Stormwater Wet Pond and Wetland Management Guidebook ). EPA has incorporated t hese mosquito control measures in the siting, des ign, 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 desi gned to encourage predation of mosquito – larvae by native fishes in tidal wetlands. T he 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 guideli nes. 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 e ffectively 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 excavati on 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 par allel-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 in troduction of invasive species (e.g., Phragmites), drying of

marsh surfaces that led to increased oxidat ion and loss of marsh s ubstrate, 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-gr id-ditched marshes, the installation of OMWM systems is often viewed as a habitat-restorat ion 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 t hat nevertheless provide m any 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 t he mandate of ”no net loss” of wetlands through pres ervation, creation, or rest oration of these valuable ecosystems, then wetland professionals must address the public perception of mosquito production and vector-borne dis ease with an integrated approach that includes providing public education and outreach while soliciting public input. Additionally, society mustSWS 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 anot her and the public during the planning, design, implementation, management and maintenance phases of wetland creation, restoration or enhancement proj ects. 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 incl ude the minimization of mosquito production to the extent practicable, done in an environmentally-compatible manner consis tent with the achievement of other objectives specifi ed for a particular project (Willott 2004).

Mosquito species have evolved to exploit a wi de 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 achi evable goal. However, current scientific understanding supports the posit ion that we can take environmentally-compatible measures to help minimize mosquito pr oduction from natural, created, or restored wetlands, and especially from many types of degraded wetlands. The SWS advocates science-based use of system design concept s 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 mos quito production in the first place.SWS Wetland Concerns Committee Page 13 7/17/09 LITERATURE CITED:

Balcer, M.D., K.L. Schmude, J. Snitgen and A.R. Lima. 1999. Long-term effects of the mosquito control agents Bti (Bacillus thur ingiensis israelensis) and methoprene on nontarget macroinvertebrates in wetlands in Wright County, Mi nnesota (1997-1998). Final report. Metropolitan Mosquito Contro l District, Saint Paul, MN, USA. http://www.mmcd.org/sprp/SprpIndex.htm

Bay, E.C. 1985. Other larvivorous fishes. p..18-24..In: H.C. Chapman (ed.) Biological Control of Mosquitoes. American Mosquito Control Association Bulletin No. 6.

Bradley, P. and F.W. Kutz (eds.). 2005. Proc. Workshop on Stormwater Management and Mosquito Control (Salisbury, MD in February, 2005, sponsored by U.S. EPA, Office of Research and Development, Ft. Meade, MD ), EPA/903/R-06/004. 71 pp. Available

online: http://www.mdcoastalbays.org/arch ive/2006/stormwaterFinal23Augbw.pdf

Brockmeyer, R.E, J.R. Rey, R.W Virnstein, R.G. Gilmor e, and L. Earnest . 1997. Rehabilitation of impounded estuarine wetlands by hydrologic reconnection to the Indian River Lagoon, Florida. Wetl ands Ecol. Manag. 4:93-109.

Brodman, R., J. Ogger, M. Kola czyk, R.A. Pulver, T.A. Bogard. 2003. Mosquito control by pond-breeding salamander larvae. Herpet ological Review. 34(2): 116-119.

Cech, J.J., Jr., and P.B. Moyle. 1983. Alternativ e fish species as predators for rice field mosquitoes in California. Bulletin of t he Society for Vector Ecology 8: 107-110.

Collins, J.N., and V.H. Resh. 1989. Guidelines for the ecological control of mosquitoes

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resources: A review. Journal of the Am erican Mosquito Control Association12: 701-712.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 Departm ent of Environmental Protection

OMWM open marsh water management

SWS Society of Wetland Scientists

WNV West Nile virusSWS 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 M egonigal 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