Mosquito Control through Source Reduction

The following is taken wholly from Chapter 4 (Mosquito Control through Source Reduction) in the Florida Mosquito Control White Paper developed by the Florida Coordinating Council on Mosquito Control. 1998. Florida Mosquito Control: The state of the mission as defined by mosquito controllers, regulators, and environmental managers. University of Florida; Vero Beach, FL, USA

Mosquito Control through Source Reduction

Source reduction, also known as physical or permanent control, typically is one part of a mosquito control agency's Integrated Pest Management (IPM) program. Source reduction is usually the most effective and economical of the mosquito control techniques available and is accomplished by eliminating mosquito breeding sites. This can be as simple as properly discarding old containers which hold water capable of producing mosquitoes or as complex as implementing Rotational Impoundment Management (RIM) or Open Marsh Water Management (OMWM) techniques which control salt marsh mosquitoes at the same time as significant habitat restoration is occurring. Source reduction is important in that its use can virtually eliminate the need for pesticide use in and adjacent to the affected habitat. The history of mosquito control source reduction efforts in Florida dates back to the 1920s when ditching of high marshes by hand or with explosives occurred. Since those early efforts, other source reduction projects included the filling of salt marshes and the creation of impoundments. While all of these techniques had mosquito control benefits, some environmental impacts occurred from their implementation. Since the early 1980s, concerted efforts to restore salt marshes impacted by mosquito control has been a management initiative.

Source reduction in freshwater habitats (e.g., flood plains, swamps, marshes) typically involves constructing and maintaining channels. These channels (=ditches) can serve the dual functions of dewatering an area before mosquito emergence can occur and also serve as harborage for larvivorous fish. Mosquito production from stormwater/wastewater habitats also can be a problem but typically can be managed by keeping such areas free of weeds through an aquatic plant management program and maintaining water quality that can support larvivorous fish. Also, tires are a severe mosquito producing habitat which can be managed by proper disposal of them. The Florida Mosquito Control/Waste Tire Abatement Grant Program provides funds to mosquito control offices to collect and properly disposal of illegally dumped tires.

4.1 INTRODUCTION

Source reduction, also known as physical or permanent control, typically is one part of a mosquito control district's (MCD) Integrated Pest Management (IPM) program. Source reduction is usually the most effective of the mosquito control techniques available and is accomplished by eliminating mosquito breeding sites. This can be as simple as properly discarding old containers that hold water capable of producing Aedes aegypti, Ae. albopictus or Culex spp. or as complex as implementing Rotational Impoundment Management (RIM). RIM is a source reduction strategy that controls salt marsh mosquitoes (e.g., Ae. taeniorhynchus, Ae. sollicitans) at the same time as significant habitat restoration is occurring. Source reduction is important in that its use can virtually eliminate the need for pesticide use in and adjacent to the affected habitat. Source reduction is appropriately touted for its effectiveness and economic benefits.

4.2 MOSQUITO PRODUCING HABITATS TO CONSIDER FOR SOURCE REDUCTION

4.2.1 Containers

Containers such as flowerpots, cans, and tires are excellent habitats for several Aedes and Culex species. Container-inhabiting mosquitoes of particular concern in Florida are Ae. albopictus and Ae. aegypti. Over the past several years in some parts of Florida, Ae. albopictus has become the primary mosquito problem. A container-breeding mosquito problem can be solved by properly disposing of such materials, covering them, or tipping them over to ensure that they do not collect water. Several Florida mosquito control agencies have extensive programs to address urban container-breeding mosquito problems through house-to-house surveillance and formalized education programs.

4.2.2 Freshwater Lakes, Ponds and Retention Areas

While it can be possible to fill small artificial ponds that produce mosquitoes, it is usually impossible to do so in natural areas (however small), large permanent water bodies, or in areas set aside for stormwater or wastewater retention. In such situations, other options that are effective in controlling mosquitoes include periodic drainage, providing deepwater sanctuary for larvivorous fish, minimizing emergent and standing vegetation, and maintaining steep banks. Culex, Coquillettidia, Mansonia, and Anopheles mosquitoes are frequently produced in these habitats.

4.2.3 Freshwater Swamps and Marshes

Environmental laws greatly restrict habitat manipulations in these areas (which can produce Culex, Anopheles, and Culiseta species), making permanent control there difficult.

4.2.4 Temporarily Flooded Locations

Pastures and agricultural lands are enormous mosquito producers, frequently generating huge broods of Aedes, Psorophora, and Culex mosquitoes. Improved drainage is one effective tool for source reduction in such habitats. The second is the use of microjet irrigation practices for those agricultural areas that require artificial watering.

4.2.5 Salt Marshes

In Florida's not so distant past, extensive coastal salt marshes produced enormous Aedes broods, making coastal human habitation virtually impossible. Several of the source reduction efforts described below have greatly reduced salt-marsh mosquito production in these marshes through high- to mid-intensity management that relies upon artificial manipulation of the frequency and duration of inundation.

4.3 SOURCE REDUCTION FOR SALT MARSH MOSQUITO CONTROL

4.3.1 Description of Florida's Salt Marshes

The first mosquito control programs in Florida were developed along the central east coast in response to the need to control salt marsh mosquitoes.

Along the central east coast of Florida, mean daily tidal ranges are small in comparison to much larger seasonal tidal variations. Wind-generated water movements can be a more important factor than are lunar tides in determining water level. The difference between the large seasonal and small daily tides results in a greater variability in inundation frequency between low and high marsh. Since low marsh is flooded by the year-round daily tidal changes and high marsh is flooded only by seasonal high tides, strong wind tides, or rainfall, a much greater acreage of high marsh compared to low marsh is created in the Indian River Lagoon (IRL). It is the large acreage of high marsh that produces salt-marsh mosquitoes because of its relatively low inundation frequency, and it is the high marsh that is targeted by most source reduction efforts.

Provost (1967) broadly classified Florida's salt marshes into three main vegetative types: Grass Marshes: Grass marshes are mostly typical of low marsh habitats and are dominated by Spartina alterniflora (cordgrass) or Juncus roemerianus (black rush). The high marsh portions of the grass marshes are usually vegetated by Distichlis spicata or Spartina patens and can be prolific producers of Ae. sollicitans. Transitional areas from low marsh to high marsh are usually narrow, as are the high marsh fringing areas themselves.

Scrub Marshes: Typical high marsh is dominated by Batis maritima (saltwort) and Salicornia spp. (glasswort). The scrub marsh can be variable in a cross-sectional area and usually lies behind a wave-action levee that limits inundation frequency.

Mangrove Swamps: Mangroves are present in both low and high marsh. In low marsh locations, mangrove swamps are dominated by Rhizophora mangle (red mangrove) while Avicennia germinans (black mangrove) and Laguncularia racemosa (white mangrove) dominate the high marsh. Red mangroves, with their extensive prop roots, protect the shoreline against erosion and typically lie waterward of the mean high water line (MHWL). Generally, a berm forms behind this mangrove fringe, effectively restricting tidal inundation frequency of the more inland sections of the swamp. Due to the current rise in sea level rise, this relationship may be changing.

Low and high marsh vegetation differs regionally. Grass marshes predominate in North Florida. Scrub marsh dominates on the central east coast from roughly St. Augustine to Indian River County and on the central west coast from Tampa Bay to Naples. From Naples and St. Lucie County southward, mangrove swamps, or mixed mangrove scrub marsh, dominate the South Florida coastal wetlands. Both scrub marsh and high mangrove swamps produce Ae. taeniorhynchus and sandflies (Culicoides spp.) in vast numbers if uncontrolled.

4.4 HISTORICAL METHODS OF SOURCE REDUCTION IN SALT MARSH HABITATS

4.4.1 Ditching

Beginning in the late 1920s, ditching of high marshes, by hand or with explosives, was done to dewater the marsh within several days of flooding. This prevented sufficient time for adult mosquito emergence and allowed larvivorous fish access to larvae. This technique was of limited success because ditches were not always dug where they were needed most, because many were promptly obstructed, especially at the ditch-estuary interface, and because fish were generally not present in sufficient numbers to provide appreciable control where the larvae occurred. Furthermore, the ditch banks made perfect sites for sandflies (Culicoides) to develop and exacerbated the biting insect problems for nearby communities.

4.4.2 Filling

In the past, using earth to fill mosquito-producing areas was a common source reduction technique along the central east coast. However, it was generally too slow and expensive. Fissures and cracks which developed in the drying dredge/fill material also produced an abundance of salt marsh mosquitoes. After a short period of use, the method was abandoned in favor of impoundment construction beginning in the 1950s. Environmental regulations have virtually eliminated the possibility of large-scale wetland filling because it is now known to severely impact this environmentally important habitat.

4.4.3 Impounding

Mosquito control impoundments consist of earthen dikes that isolate high salt marshes. Impoundments are generally artificially flooded for mosquito control purposes from May through August/September using water pumped from the adjacent estuary. Impounding and artificial flooding eliminates oviposition sites for salt-marsh mosquitoes and sandflies and has been shown both effective and economical in reducing their populations. Pumping water out of mosquitoproducing diked marsh was initially attempted as a source reduction technique but was unsuccessful because it was impossible to completely dewater the area before mosquito emergence occurred.

Historically, environmental impacts resulted from isolating and flooding these wetlands. The environmental impacts of impoundment management have received considerable scientific and regulatory attention over the past 15 years, which have resulted in management modifications designed to address both mosquito control needs and environmental benefits.

4.5 CURRENT SALT MARSH SOURCE REDUCTION TECHNIQUES

4.5.1 Environmental Considerations

Prior to the 1970s when the majority of mosquito control ditching, filling, and impoundment construction was completed, mosquito control was usually the primary consideration when manipulating salt marshes. Little concern was given to environmental issues. Today, minimizing adverse salt marsh ecological impacts must be considered when designing a source reduction project and has equal weight in the process of achieving regulatory approval.

The importance of considering both mosquito control and natural resource implications of salt marsh manipulations is evidenced by the formation of the Subcommittee on Managed Marshes (SOMM) in the Florida Statutes (Chapter 388.46) in 1986. SOMM, a subcommittee of the Florida Coordinating Council on Mosquito Control, is an advisory group responsible for providing review and comment on salt marsh management plans. SOMM, originally formed in 1983 and called the Technical Subcommittee on Mosquito Impoundments, has developed guidelines for impoundment and mosquito control ditching management plans based on current research findings. These guidelines require that management plans should be written with the mutual objectives of mosquito control, fish and wildlife resources, and water quality enhancement. The most desirable management goals appear to be those that attempt to mimic natural marsh functions while providing for mosquito control. The goal of reducing insecticide use is a factor that weighs heavily in the overall management assessment equation.

4.5.2 Ditching

Ditching can be used in both salt marsh or freshwater locations to control mosquitoes by: 1) enhancing drainage thus eliminating mosquito-producing sites, or, 2) allowing larvivorous fish access to mosquito breeding locations (this can be enhanced through the creation of permanent water bodies which act as predatory fish reservoirs). Over the past 20 years, rotary ditching as part of an Open Marsh Water Management (OMWM) system, has been implemented on both the east and west coasts of the U.S. Rotary ditching involves the construction of shallow ditches usually 4 feet wide and 2-3 feet deep, using high-speed rotary equipment which broadcasts spoil evenly over the marsh surface. A ditching network frequently connects shallow ditches to permanent water habitats, whether they be ponds or canals. Where it is impossible or impractical to connect to major waterways, a permanent pond is constructed deep enough to hold water throughout the year to harbor fish, and radial ditches connect the mosquito-producing locations to the ponds. Research demonstrating some of the ecological effects of rotary ditching has been conducted on Florida's west coast in Charlotte County and along the northern IRL in Brevard and Volusia Counties.

4.5.2.1 Benefits of a Properly Designed Rotary Ditching Plan

Rotary ditching is generally considered more environmentally acceptable than deep ditching because spoil material from these shallow ditches is evenly distributed in a very thin layer over the marsh surface. Consequently, the problem of the accumulation of overburden, with the subsequent invasion of exotic vegetation, is eliminated. Impacts to vegetation are usually limited to the ditch itself, as the tractor will climb over the vegetation allowing it to spring back, causing little damage. Marsh ditching seems to affect the vegetation as only a top-dressing of dirt might affect a lawn. Experience has repeatedly demonstrated that a properly designed rotary ditching system can greatly decrease the need for larvicide applications on the affected marsh. Rotary ditching can be cost effective and of lower management intensity when used in areas where it can be physically installed.

4.5.2.2 Environmental Risks of Rotary Ditching

Rotary ditchers broadcast the spoil indiscriminately and can throw debris great distances. Therefore, great care is necessary when working in congested areas. In loose soils, the size and shape of the finished ditch will not be maintained due to erosion from water movement through the ditch. The depth fixes the width of the ditch; therefore, a shallow ditch is also narrow. Concerns have been raised about the possible marsh hydrological changes (i.e., dewatering) that may occur from the installation of rotary ditches. This dewatering concern has been typically addressed through the installation of ditch sills, the tops of which are usually set at mean high water. The installation of sills can result in water being retained in the ditch and on the marsh surface; however, this is not always the case with some dewatering of the marsh still occurring. Though more frequent flooding of the marsh could conceivably alter soil salinities, the possible impacts to the benthic invertebrate populations have not been thoroughly investigated. Soil salinity changes also may alter native plant communities, though the introduction of nonnative plants is restricted by marsh elevation.

4.5.2.3 Rotary-Ditching Applications

Basic limitations on the use of rotary ditching revolve around the size of the ditch needed, soil types, access, adjacent terrain, and vegetation present. Marsh type candidates for rotary ditching include grass marshes, dredge spoils, temporary grassy ponds, scrub marsh, and savannas. Areas with sandy loose soil are not good ditching candidates. Ditch cleaning or new construction is possible in areas of limited woody vegetation if planned carefully. Experience has shown that poorly engineered ditches can produce more mosquitoes than preconstruction areas, as is true for any permanent control project.

Because they distribute material evenly over the marsh surface, rotary ditches do not result in the formation of spoil piles. Therefore, rotary ditching receives serious consideration for any mosquito control ditch-construction project. Environmental regulatory agencies generally will consider rotary ditching of impoundments because it usually will reduce pesticide use and will allow the maintenance of an impoundment in a free tidally exchanging condition for a longer period of the year. In some cases, it allows the impoundment to be opened permanently. Rotary ditching projects are usually undertaken by mosquito control offices and require permits from the Army Corps of Engineers, the Florida Department of Environmental Protection (FDEP) and/or a local water management district (e.g., St. Johns River Water Management District) along with local county approval.

4.5.3 Impoundments

Impounding has been used extensively along Florida's central east coast for mosquito and sandfly control. The principle is simple; keeping a sheet of water across a salt-marsh substrate prevents Aedes spp. mosquitoes from ovipositing on these otherwise attractive soils. On impounded marsh, mosquito and sandfly control is effectively achieved with a minimum of pesticide use. 4.5.3.1 Environmental Risks of Impounding

Before the 1970s, mosquito control considerations outweighed natural resource interests. This was due to the urgent need to control the tremendous salt-marsh mosquito broods and partly to the failure to recognize the ecological importance of wetlands. In the 1950s and 60s when impoundment construction occurred, little was known about the importance of high marshes and their role in estuarine productivity. Historically, black and white mangroves, Batis and Salicornia dominated many high marshes that were impounded. These plants cannot sustain continual unregulated flood heights (where the succulent plants or black mangrove pneumatophores are completely inundated). During those early years of impounding, water levels were maintained at depths that in some locations killed virtually all the existing vegetation. This left some impoundments barren of vegetation for many years, except where red mangroves intruded. Also, the earthen dike constructed around the marsh perimeter virtually eliminated the natural movement of water and organisms between the marsh and adjacent estuary. Marsh transients, those organisms that use the high marsh during a portion of their life cycle (e.g., Elops saurus (ladyfish), Centropomus undecimalis (snook), Megalops atlanticus (tarpon), Mugil spp. (mullet)), were excluded from the impounded marshes, primarily during the fall tides experienced on the east coast.

4.5.3.2 Benefits of a Properly Designed Impoundment Management Plan

Based on research conducted during the 1980s and 1990s, Rotational Impoundment Management (RIM) is currently considered the most favorable (and versatile) management technique that provides the greatest public benefit. RIM accomplishes mosquito control while still allowing the marsh to function in a close-to-natural condition for much of the year. RIM is implemented by installing culverts with water control structures through impoundment dikes to allow a seasonal connection between the marsh and estuary and installing a pump(s) to allow summer flooding of the marsh surface when it would normally be dry. Culverts serve as pathways for nutrient and organism movement. Intensive sampling has shown that fish use these culverts as ingress and egress points to the impounded marsh and that these marshes now serve as habitat for more than 100 species of juvenile fish and macrocrustaceans.

Culverts are strategically distributed around the dike. Most favorable locations are generally sites where natural tidal creeks occurred or where flushing will be optimized or evenly distributed. Culvert invert elevations are generally set at approx. -1.0 ft. NGVD (National Geodetic Vertical Datum) so that they contain water at low tide in an estuarine system where water levels typically reach 0.0 ft. NGVD at low tide. Culverts are left open during the fall, winter, and most of the spring. In the late spring, the culverts are closed and remain so through late summer/early fall (the main mosquito breeding season), during which time the marsh is artificially flooded. The water control structures attached to the culverts allow the marsh flooding height to be regulated so that the minimum height necessary for mosquito control flooding is used. Water levels exceeding control height automatically spill out into the estuary, thus preventing damage to marsh vegetation. During the closure period from approximately early May through August/September, the impounded marsh is flooded by tide, rainfall trapping, and the pumping of water as needed from the adjacent estuary, using either stationary electric or portable dieseldriven pumps. Pumping is ceased and the culverts are opened in early fall to allow the seasonally occurring fall high tides to flood the marsh. Marsh transients enter and leave the marsh on these tidal events.

RIM achieves multipurpose management by allowing the impoundment to: 1) control salt-marsh mosquito production from the marsh through means other than insecticides; 2) promote survival and re-vegetation by maintaining open periods and sufficiently low water levels during the summer flooding period, and 3) allow marine life to use the previously unavailable impounded high marsh. In order for a governmental MCD or private developer to implement a RIM plan, it usually is reviewed and endorsed by SOMM before being submitted to the permitting agencies. The agencies involved in such a RIM permitting process include the Army Corps of Engineers, the FDEP, the local water management district (e.g., the St. Johns or South Florida Water Management District) and the local county government. When undertaken by a governmental MCD, some streamlining of the permitting process for RIM projects has occurred in permitting changes adopted in 1995. Under the State's newly developed Environmental Resource Permit (ERP), a Noticed General Permit is now granted to MCDs for the installation of culverts in impoundments for non-mitigation enhancement projects. While some review of the project is still necessary, this streamlined permit process should speed up the regulatory process.

4.5.4 Current Efforts in Salt Marsh Management

RIM management and rotary ditching as described above are marsh management techniques that are well accepted by both mosquito control agencies and those responsible for protecting natural resources. Virtually all of the IRL marshes have been impacted in some way; therefore, management diversity may be the best solution for the future. Toward that goal, SOMM has been involved in a project to develop regional management plans for IRL impoundments and marshes. This planning project is being accomplished by regionalizing the lagoon into 10 management areas and assigning to each marsh in each group an optimal management scenario based on current best management information. In addition to RIM and OMWM utilizing rotary ditching, appropriate techniques include: Open marsh-lagoon connection, RIM modifications with nearcontinual pumping during the closed period for water quality improvement, RIM management with modifications to enhance wading bird feeding opportunities, waterfowl management and stormwater retention, to name just some of the possibilities. That planning document provides assistance to governmental agencies and private developers for specific marshes that become targeted for management. However, as always, recommendations made today can change tomorrow, as further scientific information becomes available. (See Appendix I for a listing and description of recognition given to mosquito control professionals for their source reduction efforts that take into account environmental considerations.)

4.6 SOURCE REDUCTION IN FRESHWATER HABITATS

Source reduction for mosquito control in freshwater habitats typically involves constructing and maintaining channels (ditches) to reduce mosquito production in areas such as flood plains, swamps, and marshes. The principle that directs source reduction work entails manipulating water levels in low-lying areas to eliminate or reduce the need for spraying applications. Two different mosquito control strategies or approaches are considered when performing freshwater source reduction. One strategy involves reducing the amount of standing water or reducing the length of time that water can stand in low areas following significant rainfall events. This type of strategy involves constructing channels or ditches with control elevations low enough to allow for a certain amount of water to leave an area before immature mosquitoes can complete their life cycle.

Another strategy involves constructing a main central ditch with smaller lateral ditches at the lowest elevations of intermittent wet areas to serve as a larvivorous fish reservoir. As rainfall increases, larvivorous fish move outward to adjacent areas to prey on immature mosquitoes, and as water levels decrease, larvivorous fish retreat to water in the ditches. Weirs are constructed in main ditches to decrease water flow, decrease emergent aquatic weeds, prevent depletion of the water table, and allow larvivorous fish year-round refuge.

From a historical perspective, the construction of most source reduction projects occurred between the 1940s through the mid-1960s. Initially, these drainage projects were designed to reduce the production of Anopheline mosquito species to lower the incidence of malaria in Florida. Later, drainage projects were constructed to help control other vector species as well as nuisance species. Local mosquito control agencies wanting to construct drainage projects had to obtain approval from the state mosquito control office, originally located in the State Board of Health. Entomological data to support/justify the merit of projects along with design specifications had to be provided in order to obtain approval. Once projects were approved by the State, construction and maintenance activities were regulated by the State to ensure compliance with good mosquito control practices. In addition, for a period of more than twenty-five years, a specific type of financial aid (State II Aid) was provided to local MCDs the purpose of supplementing the costs associated with constructing and maintaining source reduction projects.

At this point in time, very few, if any, MCDs are involved in construction of new drainage projects because of environmental restrictions associated with obtaining permits. However, several MCDs are involved in performing maintenance on existing drainage systems. This maintenance includes cutting, mowing, or herbiciding overgrown vegetation and excavating built up spoil material. Florida law provides a permit exemption for mosquito control maintenance activities. This maintenance exemption allows mosquito control agencies to maintain the systems, provided that the sizes of the systems are not expanded beyond original design specifications. One important provision of the exemption states that up to 10,000 cubic yards of spoil material can be excavated from a project without a permit, provided that the material is deposited on a self-contained upland site.

Over the past several decades, urban development has occurred in areas of Florida where mosquito control drainage ditches have existed as the primary drainage systems. If these drainage systems are expanded to meet modern stormwater management specifications, mosquito control maintenance exemptions are no longer valid. In many cases, maintenance responsibility for mosquito control projects has been taken over by city and county public works departments and integrated into their comprehensive stormwater management programs.

4.7 STORMWATER & WASTEWATER MANAGEMENT

(see Appendix II for a description of East Volusia Mosquito Control District's specific stormwater plan)

Florida largely depends on potable water pumped from aquifers supplied by rainfall. Much of Florida has flat topography with sandy soils resulting in a variety of percolation rates and water table depths. This makes the management of stormwater and wastewater very important, and when done without sound engineering, poor construction or improper maintenance, can result in considerable mosquito problems.

From a legislative perspective, very little has been done to prevent the production of disease vector or nuisance mosquitoes from either stormwater or wastewater facilities. Wastewater facilities are regulated under FDEP. The current trend of eliminating small package plants and hooking into regional systems has helped. Stormwater is regulated by FDEP or the appropriate water management district, counties, and municipalities. In 1982, the Florida Department of Health and Rehabilitative Services (FDHRS) (through the efforts of William Opp) and the Florida Department of Environmental Regulation (FDER) developed the original state criteria for considering mosquito problems resulting from stormwater facilities. The 72-hour recovery period associated with design criteria for retention and filter/underdrain systems was put in the rule at FDHRS's suggestion solely to minimize mosquito production.

A few counties and municipalities have language prohibiting mosquito production in stormwater treatment facilities. This language was largely due to the efforts of William Opp of HRS in the late 1970s and early1980s to develop some guidelines for engineering mosquito-free facilities. East Volusia Mosquito Control District built upon this work in the early 1990s by developing their own local Best Management Practices (BMP) or Mosquito Control in Stormwater Management Facilities (included in this document).

Currently the U.S. Environmental Protection Agency (EPA) is involved in permitting stormwater management as it relates to Municipal Separate Storm Sewer Systems (MS4s) and the discharge of Stormwater Association with Industrial Activity. These permits represent an expansion of Florida's State/WMD stormwater program in that they address existing systems, not just new development. The impact on mosquito control is expected to be relatively minor, since these permits do not typically require the installation of structural controls (BMP) such as retention or detention ponds for compliance.

Research into mosquito problems associated with stormwater and wastewater facilities has been limited. Dr. George O'Meara of Florida Medical Entomology Laboratory (FMEL) performed some studies in the 1980s on wastewater treatment facilities. More recently, Dr. Fred Santana of Sarasota County studied stormwater management facilities and mosquito problems associated with them. A few other researchers also have looked into this problem.

Currently there is a wide range of mosquitoes produced in these facilities including floodwater Aedes and Psorophora species in intermittently wet facilities, Culex and Anopheles species associated with permanent or semipermanent wet facilities, and Mansonia and Coquillettidia species associated with floating or emergent vegetation. The Aedes, Psorophora, Mansonia and Coquillettidia species are the most pestiferous to humans. Mosquito control efforts in infested areas include larviciding, hand and mechanical vegetation management, herbiciding, barrier treatments, ultra low volume (ULV) adulticiding, stocking with larvivorous fish, and the installation of reservoirs for larvivorous fish.

Mosquito production can be engineered out of stormwater and wastewater facilities but not always easily. Permanent water ponds can be kept clean of weeds with a water quality sufficient to support mosquito-eating fish. Dry facilities can be designed to dry down in three days to prevent floodwater mosquito production, but some standing water beyond the three-day period may occur due to intermittent rainfall common to Florida in the summertime. More details are included in the enclosed BMPs developed by the East Volusia Mosquito Control District.

4.7.1 Conclusions

• Ideally, all agencies involved in regulating stormwater and wastewater facilities should add language striving to minimize, and where possible, eliminate, mosquito production in those facilities making certain that should mosquito production occur from these facilities, it is not a nuisance or public health threat. In addition, a method for resolving problems to maintain compliance with this goal is desirable, but it is recognized that this is a major undertaking due to the large number of stormwater facilities statewide. Partnerships between state and local government agencies (in particular local field inspectors) could be beneficial in helping to meet compliance requirements. Research is needed to establish testing/monitoring techniques and thresholds to allow applicants, operators, and independent inspectors to determine compliance with such a goal.

• All agencies involved in regulating stormwater and wastewater facilities should recognize that some wetland plantings, while providing habitat for fish and wildlife as well as other ecological benefits, could create mosquito larval habitat. This fact should be taken into account in system design, and plantings that do not contribute to mosquito problems should be used.

• There should be a state recognized and published BMPs for mosquito control in stormwater and Wastewater Management Facilities. This would provide an educational tool to serve as a guide to designers, builders, and operators. The East Volusia Mosquito Control District has such a policy, which is included as Appendix II.

• Mandatory mosquito biology and control training should be part of all stormwater and wastewater certification programs.

Finally, mosquito problems in stormwater and wastewater facilities are easy to prevent and sometimes easy to fix. The approaches are nonchemical and environmentally sensitive, and they have the potential to reduce mosquito populations in all areas.

4.8 MOSQUITOES ASSOCIATED WITH WASTEWATER

In many parts of Florida, clean freshwater for domestic, agricultural, or industrial uses is becoming a critical resource. Wastewater recycling and reuse help to conserve and replenish freshwater supplies. Floridians daily produce approximately 100 gallons of wastewater per capita from domestic sources alone. Concern for water quality conditions in lakes, rivers, and marine areas has resulted in the enactment of new state laws that will greatly limit future disposal of wastewater into these aquatic systems. To adjust to these changing conditions, many communities must implement wastewater reuse and recycling programs. Mosquito problems are frequently associated with some of the conventional wastewater treatment operations, and the expanded use of wastewater recycling and reuse may inadvertently create even more mosquito habitats.

4.8.1 Domestic Wastewater

4.8.1.1 Septic Systems

Nearly 40% of Florida's households use on-site treatment systems, such as septic tanks and associated drain fields. With proper soil porosity, sufficient lateral fields, and low human congestion, these systems are safe and efficient. The wastewater in a properly located and maintained septic tank system will percolate into the subsoil without causing surface water accumulation that may induce mosquito production. Yet, when these systems are placed in locations with inappropriate soil conditions, wastewater will flow laterally, often into nearby swales and ditches.

4.8.1.2 Package Plants

Most central wastewater facilities in Florida are relatively small, treating less than 100,000 gallons of wastewater daily. The most common type of small system is the so-called package plant, which often is used by private companies when establishing new subdivisions and related developments. Some of these package plants provide inadequate wastewater treatment because the are poorly maintained or operated beyond their capacity. Generally, package plants discharge treated wastewater into small holding ponds. When these ponds receive poorly treated wastewater, mosquitoes may become abundant, especially when the ponds are invaded by various species of aquatic plants. If aerators, pumps, and related components of package plants are not functioning properly, then mosquito production may not be confined to just the holding ponds.

4.8.1.3 Large Treatment Facilities

These systems often have larger holding ponds that are less likely to be invaded by mosquitoes than are the smaller ponds normally associated with package plants. Often the major mosquito problems associated with large municipal and county wastewater treatment facilities are confined to the advanced treatment phase of the overall process. Techniques used to improve water quality conditions beyond the levels obtained in the secondary treatment process include spray irrigation, rapid-dry ponds, aquatic plant/wastewater systems, and the use of natural or modified wetlands.

4.8.1.4 Spray-Irrigation Systems

Secondarily treated wastewater is used to irrigate golf courses, road medians, pastures, sod fields, citrus groves, and other types of crops. During the rainy season, it is not uncommon for spray fields to become waterlogged, particularly those in low-lying areas with high water tables or in poorly drained soils. Under these conditions, the continued application of spray irrigation will result in the accumulation of surface water, thus providing aquatic habitats for a variety of mosquito species.

4.8.1.5 Rapid-Dry Ponds vs. Holding Ponds

Rapid-dry ponds are classified as a dry-retention system. Water flows into the pond and then percolates into the soil. By contrast, holding ponds are primarily flow-through systems. Typically, water enters and leaves the holding pond in some type of pipe. Soil percolation is an optional feature in holding ponds. Due to the regular inflow of wastewater, holding ponds are normally full, and thus they represent a type of wet-detention system. Rapid-dry ponds that fail to dry out fast enough produce mosquito problems similar to those found in areas where surface water has accumulated due to excessive amounts of spray irrigation.

4.8.1.6 Wastewater/Aquatic Plant Systems

At some sewage treatment facilities in Florida, certain species of aquatic plants (e.g., water hyacinths) have been added to human-made ponds containing secondarily treated wastewater for nutrient removal and biomass production. Mosquito problems can be produced in this type of system if the inflow has received an inadequate secondary treatment. Effective nutrient removal requires periodic harvesting of a portion of the standing crop.

4.8.1.7 Wetlands

At some locations in Florida, secondarily treated wastewater is pumped into wetland areas. Earthen dikes are often used to increase the water-holding capacity of the various types of wetlands that are receiving discharges from sewage treatment facilities. The responses of mosquito populations to wastewater inundations vary depending upon the type of wetland. For example, coastal salt marshes and mangrove swamps are noted for producing large broods of pestiferous mosquitoes. Highly effective mosquito control has been achieved by surrounding these brackish wetlands with dikes and then flooding the enclosed area with water. Usually brackish or freshwater is used to fill mosquito control impoundments. However, at a few locations these impoundments have been operated effectively with secondarily treated wastewater as the influent.

The various types of freshwater wetlands in their natural condition provide suitable aquatic habitats for a variety of mosquito species. The addition of treated wastewater to these aquatic systems usually does not lead to mosquito abatement, but more often it changes the relative abundance of the mosquito species, which may produce new mosquito problems.

4.8.2 Agricultural and Industrial Wastewater

Many commercial operations have on-site treatment facilities for decreasing nutrient loads from their wastewater, and generally, they use techniques similar to those applied to domestic wastewater. The quantity of wastewater produced at some commercial locations, such as those processing certain crops, may be highly variable during the year. Therefore, the amount of surface water in the holding ponds or spray fields used in the wastewater treatment may fluctuate considerably, thereby contributing to the production of certain species of flood-water mosquitoes. Wastewater from feed lots and dairy barns is often placed in holding or settling ponds without any prior treatment. Several mosquito species of the genus Culex can become extremely abundant in these ponds, especially in the absence of aquatic plant control.

4.8.3 Major Pest and Disease-Vectoring Species

4.8.3.1 Culex

Throughout much of southeastern United States, the dominant species of mosquito in wastewater ponds and lagoons is usually Culex quinquefasciatus. Major exceptions to this general pattern occur in both central and south Florida where Cx. nigripalpus is often seasonally more abundant than Cx. quinquefasciatus. Here, especially in the southern half of peninsular Florida, Cx. nigripalpus is usually the dominant wastewater Culex in the summer and fall, whereas Cx. quinquefasciatus is more common in the winter and spring. Human activities are responsible for establishing the vast majority of the aquatic habitats used by Cx.. quinquefasciatus, the so-called southern house mosquito. A much wider range of larval habitats, including both artificial and natural aquatic systems, is used by Cx. nigripalpus. In large wastewater ponds, immature Cx. quinquefasciatus are generally most abundant near the inflow area where the nutrient loads are normally the highest. By contrast, immature Cx. nigripalpus are more evenly distributed in wastewater ponds.

Culex salinarius, another common mosquito in wastewater, is like Cx. nigripalpus in terms of its range of larval habitats, but its seasonal pattern of abundance is similar to that found in Cx. quinquefasciatus. Culex nigripalpus and Cx. salinarius inhabit not only semipermanent ponds but also more ephemeral habitats, such as temporary pools in spray-irrigation fields. Occasionally, immature Cx. restuans may become very common in a wastewater system. Fortunately, Cx. restuans populations are inactive during much of the year in most of peninsular Florida. Culex salinarius is the most pestiferous wastewater Culex because it feeds mainly on mammals, while females of the three other species are either general or primarily avian feeders. However, Cx. nigripalpus is the species with the greatest impact because it is the dominant Culex in peninsular Florida during the summer and fall, occurs in wastewater systems that vary over a wide range of nutrient loads, and is the primary vector of St. Louis encephalitis (SLE).

4.8.3.2 Aedes and Psorophora

Unlike Culex, whose eggs hatch within a few days after being laid in rafts on the water surface, Aedes and Psorophora lay their eggs individually on moist substrate with hatching occurring only after the eggs have been flooded. Consequently, Aedes and Psorophora are seldom found in wastewater systems where there is little or no variation in surface water levels. However, poorly designed, improperly operated, or inadequately maintained systems often lead to conditions that are ideal for an invasion by floodwater mosquitoes. Poorly drained spray-irrigation fields often become water logged, especially during the rainy season. Under these conditions, many broods of Ae. vexans and Psorophora columbiae can be produced in a single season. Land application of wastewater may increase the salt content of the soils. Under these conditions, inland sites may become suitable aquatic habitats for salt marsh mosquitoes. Aedes sollicitans has become a major pest species at some wastewater disposal or recycling sites.

4.8.3.3 Mansonia and Coquillettidia

Immature Mansonia dyari, Ma. titillans, and Coquillettidia perturbans do not breathe at the surface; rather, they obtain oxygen from the root hairs of various species of aquatic plants. The larvae and pupae of these mosquitoes stay attached to the plants for extend periods. Immature Ma. dyari are found almost exclusively in association with water lettuce, Pistia stratiotes, whereas Ma. titillans use several species of aquatic plants, with water hyacinth (Ecihhornia crassipes) and water lettuce being common hosts. Rooted and floating cattails (Typha spp.), especially when floating in a mat, are the principal host plants for Cq. perturbans. Of the three species dependent upon aquatic plants, Cq. perturbans is the most aggressive biter. It is an opportunistic blood feeder, occasionally taking multiple blood feeds. These behavioral traits enhance the mosquito's potential for vectoring certain viruses. Mansonia dyari females are less likely to feed on humans than are Ma. titillans females. Nevertheless, at those locations where Ma. dyari is extremely abundant it may be an important component in the enzootic cycles of SLE transmission.

4.8.4 Mosquito Control

The best approach is to avoid a mosquito problem in the first place by incorporating into the design and operation of wastewater treatment systems features that will either preclude or greatly limit mosquito production. Special attention should be directed at the items listed below.

4.8.4.1 Operating Capacity

Many systems provide inadequate wastewater treatment because the amount of inflow regularly exceeds treatment capacity. Treatment facilities must be designed and constructed to handle current and future demands that are based on realistic projections. Moreover, facilities need to be properly maintained to prevent any loss in operating capacity. Although wastewater treatment is expensive, cutting costs by overloading treatment facilities is counterproductive in the long term.

4.8.4.2 Water Quality

Wastewater should receive at least a good secondary treatment and preferably some advanced treatment before it is placed in detention/retention areas. Land applications, such as irrigation projects, should be used to complement rather than substitute for good secondary treatments. Poor water quality is a major factor contributing to Culex mosquito problems. Improved secondary and advanced treatments decrease the likelihood that Cx. quinquefasciatus and Cx. nigripalpus will oviposit into the aquatic systems, make habitats more suitable for fish and other mosquito predators, and increase the effectiveness of various mosquito larvicides.

4.8.4.3 Wet-Detention Ponds

Larger ponds are much more desirable than are smaller ones (i.e., those with < 0.1 acre of surface area). In fact, smaller ponds and various types of wastewater holding tanks may require surface agitation from a sprinkler or an aerator to deter invasion by Culex mosquitoes. The banks should be relatively steep and the minimum water depth should be at least 2 feet. Methods for preventing seepage should be incorporated into the design and construction of holding ponds. Water levels in wet-detention ponds should be kept constant. If ponds must be drained for maintenance, they should be equipped for rapid and complete drainage. These drainage/refill episodes should be infrequent. Debris and excessive vegetation should be removed from the banks and shoreline. The surface of wet-detention ponds should be kept free of floating and immersed aquatic plants. The deliberate induction of aquatic plants such as water hyacinths for biomass production or improving water quality, should be limited to ponds receiving good secondarily or advanced treated wastewater. When water hyacinths and other aquatic plants are used for nutrient removal, they must be protected from insects, pathogens, and cold weather. Otherwise the dead plants will release nutrients back into the wet-detention pond and thereby increase the likelihood of generating a mosquito problem. The harvesting schedule must be adjusted for variation in the plant's seasonal growth pattern. Failure to harvest the plants on time also increases the chances for a mosquito outbreak.

4.8.4.4 Dry-Retention Areas: Rapid-Dry Ponds and Spray-Irrigation Fields

In theory, the wastewater applied to these ponds and fields should rapidly percolate into the soil so that surface water is present for just brief periods (less than a few days). In practice, standing water is often present for longer periods. Even if 90 to 95% of the wastewater rapidly enters the soil, the amount of surface water remaining can cause major mosquito problems. Dry-retention areas must be restricted to sites with soil and water table conditions that will allow for the rapid absorption of all wastewater. The rate of application needs to be adjusted for seasonal patterns in rainfall amounts and water table levels and for long-term changes in the soil's water holding capacity.

Depressions, potholes, and related irregularities should be removed from dry-pond bottoms and spray-irrigation fields. In systems covered with grasses, mowing should be done without creating tire ruts, and the cuttings should be removed. Even when rapid-dry ponds and spray-irrigation fields operate satisfactorily, seepage to adjacent lowlands may create or aggravate mosquito problems. Therefore, the design of dry-retention areas should include provisions for adequate drainage in neighboring areas.

4.8.4.5 Wetlands

Environmental mandates and budgetary conditions may greatly limit the use of either aquatic plant management or mosquito larvicides for controlling mosquitoes in freshwater wetlands that receive wastewater. Baseline information on mosquito production in the wetlands should be obtained before the introduction of the wastewater. Then it will be possible to document additional mosquito production due to the input of wastewater. Access roads should be made available so that all major sections of the wetlands can be monitored periodically for mosquitoes. If plans call for deliberately adding aquatic plants to a wetlands/wastewater system, efforts should be made to avoid using plant species that provide especially favorable microhabitats for mosquitoes. Flow rates and nutrient loading should not exceed the carrying capacity of the area. Wetlands receiving wastewater should be located away from residential and commercial areas. Future development should be limited to maintain buffer zones.

4.8.4.6 Larvicides

Several different types of larvicides are available for controlling mosquitoes. Generally, these larvicides are least effective in wastewater systems. The flow-through nature of many wastewater treatment, reuse, and recycling operations rapidly diminishes the effectiveness of many larvicides. Bacteria and other components of wastewater quickly break down or inactivate some larvicides. Increasing the dosage rate and the number of applications or using slow-release formulations may be required to achieve adequate control. At sites where mosquito outbreaks are large and frequent, using larvicides, which at best would provide only temporary control, may not be a costeffective approach. Larvicide operations must be supported with a quality inspection program.

Potential mosquito production sites must be identified and frequently inspected for mosquitoes. Larvicide applications should be integrated with other mosquito abatement measures, such as aquatic plant management and measures directed at improving water quality. Larvicides should not interfere with the level of mosquito control provided by natural predators and parasites.

4.9 AQUATIC PLANT MANAGEMENT AND THE EFFECTS ON MOSQUITO POPULATION

This section describes the practices used to control mosquitoes and aquatic plants associated with freshwater environments only. Salt marsh environments are discussed in other sections of this document.

Certain mosquito species use various aquatic plants as a primary habitat for egg deposition and larval development. Because aquatic plants can, at times, produce heavily vegetated stands, the use of conventional mosquito management techniques, such as biological and chemical control, may be ineffective. Therefore, removal of the habitat may be the only means of reducing these mosquito populations to a desired level.

Aquatic plant management in Florida can have a positive effect on the control of mosquito populations. A primary goal in reducing mosquitoes that use aquatic plants is to eradicate or, at the very least, manage the aquatic plant communities at the maintenance or lowest feasible level. 4.9.1 Mosquitoes

The three most important mosquito species that use aquatic plants in Florida are Ma. dyari, Ma. titillans, and Cq. perturbans. The following descriptions are partially reprinted from the Florida Mosquito Control Handbook.

Mansonia dyari is found in permanent lakes and ponds. This species is most closely associated with water lettuce but also occurs on water hyacinth, pickerel weed (Pontederia), and arrowhead (Sagittaria). The egg masses are attached to water lettuce leaves and, after hatching, the larvae and pupae attach permanently to the roots, getting their oxygen from the plant tissues. The females will bite humans but seldom become pests. In Panama, this species is a major vector of SLE, but its relationship to the SLE virus in Florida is unknown.

Mansonia titillans is also found in permanent lakes and ponds. This species is most closely associated with water hyacinth but also occurs on water lettuce, pickerel weed, and arrowhead. This is a tropical species found only in the southern half of the state. The egg masses are laid on the underside of floating leaves, and the larvae and pupae attach to and derive their oxygen from the roots. It can be a pest to humans near its breeding sites. In South America, this species is a major vector of Venezuelan encephalitis.

Coquillettidia perturbans is found in permanent lakes and ponds with cattails, sedges, maidencane (and other Panicum grasses), and arrowhead. This large black and white mosquito is a severe pest in inland Florida. It breeds in established permanent freshwater marshes containing emergent vegetation where there is a layer of detritus on the marsh bottom. The eggs are laid in a raft on the water surface and the immature forms attach to the roots of the emergent plants. This aggressive mosquito is active for short periods at dusk and commonly flies three to five miles, often much farther. Females bite both humans and birds. This species is an important vector of eastern encephalitis to humans throughout the eastern U.S., wherever it is associated with Culiseta melanura.

4.9.2 Aquatic Plants

The three most important aquatic plant species that provide a habitat for mosquitoes in Florida are water lettuce, water hyacinth, and cattails. The following descriptions are reprinted from the Aquatic Plant Identification Deck by Victor Ramey.

Water lettuce is a floating plant. Experts disagree as to whether water lettuce is a native or has been introduced. Water lettuce occurs in lakes, rivers, and canals, occasionally forming large dense mats. As its name implies, water lettuce resembles a floating head of lettuce. The very thick leaves are light dull green, hairy, and ridged. There are no leaf stalks. Water lettuce roots are light-colored and feathery. Its flowers are inconspicuous.

Water hyacinth is a floating plant. This exotic nuisance grows in all types of freshwaters. Water hyacinths vary in size from a few inches to more than three feet tall. They have showy lavender flowers. Water hyacinth leaves are rounded and leathery, attached to spongy and sometimes inflated stalks. The plant has dark feathery roots.

Cattails are among the most common of all aquatic plants. They can reach eight or more feet tall and grow prolifically from thick underground rhizomes. Cattails often dominate large areas, especially where water levels fluctuate. Cattails get their name from their cylindrical flower spikes that can be more than one foot long. The flower spikes are densely packed with tiny flowers. Cattail leaves are strap-like, stiff, and rounded on the back. The leaves are sheathed together at their bases. Therefore, cattail plants appear to be flattened from the side. Leaves are straight in the bottom half but twist and spiral in the top half.

4.9.3 Surveillance

If adult Mansonia mosquito species are discovered through routine surveillance monitoring, a thorough survey of the immediate area should be conducted to locate freshwater sources containing water hyacinths and water lettuce. If a suspected freshwater source is found, a larval survey should be conducted. Mansonia mosquitoes attach to the root structures of floating aquatic plants. If disturbed, the larvae will immediately release and fall to the bottom. Because of this, a mosquito dipper is an inappropriate sampling tool. A good method for collecting Mansonia larvae is to place a shallow pan under the floating aquatic vegetation. Care must be taken not to disturb the aquatic plants or surrounding area. Once the pan is in place, it and the aquatic plant must be lifted slowly out of the water. Clean water may have to be added to the pan to accurately view and count any mosquito larvae. This method requires a great deal of patience and practice.

Coquillettidia perturbans can fly several miles. Therefore, a more widespread survey of freshwater sources containing cattails may be necessary. The eggs and larvae of this mosquito are usually found in the detrital material at the base of the aquatic plants. A mosquito dipper or siphon can be used to collect the larvae. However, the water may have to be placed in a pan containing clean water for accurate viewing and counting.

4.9.4 Mosquito Control Measures

The use of biological control methods, such as mosquito fish, is usually not effective. The aquatic vegetation is too dense for predators to gain access to the mosquito larvae. Chemical control methods, such as the larvicides Bacillus thuringiensis israelensis (Bti) and Abate®, may be effective if the product is applied directly to the areas containing mosquito larvae. This may be difficult and labor intensive if the aquatic vegetation is dense. Monomolecular surface films are not effective under all climatic and breeding situations found in Florida. In general, conventional mosquito control methods are not effective tools in reducing mosquitoes associated with aquatic plants.

4.9.5 Aquatic Plant Management Measures

Eradication or maintenance level control of aquatic plants is the best method of mosquito control. There are three basic types of aquatic plant management.

Chemical control involves the use of aquatic herbicides to eradicate or manage the aquatic vegetation. Depending on the amount and accessibility of the vegetation, a backpack, truckmounted, boat-mounted, or aircraft-mounted sprayer can be used. The aquatic herbicides used are specific for the aquatic plants. Diquat is used to control water lettuce, a 2,4-D amine is used for water hyacinths, and glyphosate is primarily used for cattails. Chemical control can be cost effective if the aquatic plants are managed at a maintenance level.

Biological control involves the use of insects or pathogens to eradicate or manage the aquatic plants. The water lettuce weevil and water hyacinth beetle have been used with limited success. At the present time, there is no effective biological control for cattails. There have been a few successful large-scale biological applications to date. However, more research is needed to adequately address some of the problems found. Biological control has proven to be very cost effective.

Mechanical control is a method in which equipment or tools are used to physically remove the aquatic vegetation. Examples would include aquatic harvesters, bucket cranes, underwater weed trimmers, and machetes. Mechanical control is limited to areas that are easily accessible to the equipment. Also, mechanical control can be labor intensive and extremely expensive.

4.10 WASTE TIRE PROGRAM IN FLORIDA

4.10.1 Tires as Mosquito Producers

Tires have been a mosquito breeding problem since the first discarded tire filled with water. Waste tires have been legally and illegally accumulating in Florida for the past several decades. The legal accumulations usually take the shape of a somewhat organized pile containing up to several million tires. Illegally dumped tires may be scattered about from singly up to piles containing 40 to 50 thousand carcasses. Unfortunately, most of the problem tires are not in large piles, but scattered about, making removal difficult and, at best, labor intensive.

The design of tires makes them ideal breeding sites for several species of mosquitoes, of which, some are very important vectors of disease. The 20-80 rule probably applies to waste tires. Of the mosquito problems associated with waste tires, it probably is safe to say that 20% of the tires are responsible for 80% of the problem.

Until the mid-1980s, waste tires were considered more of a nuisance and environmental threat than the possible foci of mosquito-borne disease epidemics. This changed in 1985 when a substantial breeding population of Ae. albopictus was discovered in Houston, Texas. It is probable that this population arrived from Japan as eggs deposited inside used tires. In 1986, this species was found in an illegal tire pile in Jacksonville. It was found in 62 counties in 1991 and by 1994 was established in every county in Florida.

The potential importance of Ae. albopictus and waste tires became apparent in June 1991 when adult specimens, collected from a large tire pile in Polk County tested positive for the eastern equine encephalitis virus. This discovery called attention to a problem of enormous magnitude. Discarded automobile and truck tires are the preferred habitat of Ae. albopictus. Chemical treatment of tire piles to control either larval or adult stages is much more difficult than most routine applications and may not be fully effective. Shredding tires, or otherwise rendering them incapable of holding water and supporting mosquito production, is preferable to attempting control through the application of larvicides and adulticides. However, in the case of large piles, such as the one in Polk County, which contained an estimated 4.5 million tires, it may take two years or more to complete the shredding and cleanup process.

4.10.2 Waste Tire Disposal Regulations

In an effort to promote recycling, slow the growth of landfills, and reduce pollution, a comprehensive solid-waste bill was enacted in 1988. This legislation empowered FDEP to regulate the storage, transportation, processing, and disposal of waste tires. Under this bill, no one is allowed to have more than 1,000 tires except at a solid-waste management facility or a waste tire processing facility. Transporters are required to register each truck used to haul tires with FDEP, dump only at approved locations, and maintain records of where they got the tires and where they put them. Processors with fixed-site facilities are allowed to have more than 1,000 waste tires in storage but must comply with storage standards set by the rule. Landfills are allowed to collect as many tires as are brought in but must have the tires on hand processed every 90 days. Landfills are allowed to bury tires that have been cut into eighths or smaller pieces. Most landfills have the tires shredded to a four-square-inch size that they can use as daily landfill cover. The FDEP also is involved in eliminating the state's large, illegal tire sites. If a site owner is unable or unwilling to abate his site, FDEP can gain possession of the site through the court, process and remove the tires, and seek recovery of costs.

The legislation also established a waste tire fee of $1.00 to be collected on each new tire sold at retail. The waste tire fee generates more than $16 million per year, which goes into the Solid Waste Management Trust Fund. Of this amount, 55% goes to counties. The grants to counties are made on a per capita basis and are being used for subsidizing tipping charges at landfills, paying private firms to shred tires, purchasing shredders, and financing research.

In addition to the above, at least 10% of the waste tire fees collected are allocated to local mosquito control agencies for the purpose of abating and providing mosquito control relating to waste tire sites, other tire piles and waste-debris sites identified as mosquito breeding areas. Only mosquito control agencies approved by FDACS may receive these funds. During the first year (FY 92/93), the funds were administered by FDER and were distributed on a reimbursable basis. Since then, $1,600,000 annually has been transferred to FDACS for administering. Direct oversight of the program is the responsibility of the Bureau of Entomology and Pest Control. Currently, 46 approved mosquito control programs in 43 counties receive state aid. In addition to all other state funds, every approved MCD is eligible to receive Mosquito Control/Waste Tire Abatement Grant funds. Each participating county receives a minimum of $15,000. Any remaining funds are distributed to participating counties on the basis of population. If more than one local MCD exists in a county, the funds are prorated between the districts based on the population served by each district.

Each MCD receiving Mosquito Control/Waste Tire Grant funds is required to submit a monthly report of activities regarding its mosquito control activities associated with waste tires. The report provides sufficient information to determine how the funds are being used and ensures adequate attention to waste tire removal and other related elements of the program. During FY 93/94 the participating agencies received approximately $1.5 million in Mosquito Control/Waste Tire Abatement Grant funds and spent about $3.9 million on waste tire related mosquito control activities, which include cost of chemicals, equipment, labor, and landfill tipping fees. They received approximately the same amount in FY 94/95 and incurred about $4.6 million in costs. Following the enactment of the solid-waste bill in 1988, FDEP identified and targeted for cleanup 27 sites that contained more than 100,000 tires. Only four of those sites remain today. This reduces the waste tire problem to a more manageable level but does not alleviate the mosquito breeding problems caused by the many thousands of tires scattered throughout the state that have been illegally discarded to avoid dumping fees. This is where mosquito control programs can make a real difference. During the first two years that mosquito control agencies participated in the waste tire program, they were responsible for the collection and removal of approximately 730,000 discarded tires.

The removal of waste tires will go a long way toward reducing the populations of Ae. albopictus and the threat of dengue and possibly eastern equine encephalitis (EEE) and yellow fever. However, as tires disappear from the environment, the mosquitoes that found them to be such an attractive habitat will quickly adapt to almost any type of container that will hold water. In the final analysis, premise sanitation is the key to controlling this mosquito problem. Mosquito control workers have daily contact with the public and are uniquely suited to the task of informing the citizens what they can do to eliminate mosquito breeding habitats around their residences.

4.11 REFERENCES AND GENERAL READING

Bruder, K.W. 1980. The establishment of unified Open Marsh Water Management standards in New Jersey. Proc. N.J. Mosq. Control Assoc. 67:72-76.

Carlson, D.B. 1987. Salt marsh impoundment management along Florida's Indian River lagoon: historical perspectives and current implementation trends, pp. 358-371. In: Proceedings of a Symposium on Waterfowl and Wetlands Management in the Coastal Zone of the Atlantic Flyway, W.R. Whitman and W. H. Meredith (eds).

Carlson, D.B. and J.D. Carroll, Jr. 1985. Developing and implementing impoundment management methods benefitting mosquito control, fish and wildlife: a two year progress report about the Technical Subcommittee on Mosquito Impoundments. J. Fl. Anti-Mosq. Assoc. 56:24- 32.

Carlson, D.B. and P. D. O'Bryan. 1988. Mosquito production in a rotationally managed impoundment compared to other management techniques. J. Am. Mosq. Control Assoc. 4:146- 151.

Carlson, D.B. and J.R. Rey (eds). 1989. Workshop on salt marsh management and research. J. of Fl. Anti-Mosq. Assoc., Bulletin #1, 19 p.

Carlson, D.B., J.R. Rey and J.D. Carroll (eds). 1992. 2nd workshop on salt marsh management and research. J. of Fl. Mosq. Control Assoc., Bulletin #2, 41 p.

Carlson, D.B., J.R. Rey and J.D. Carroll (eds). 1997. 3rd workshop on salt marsh management and research. J. of Fl. Mosq. Control Assoc., Bulletin #3, 48 p.

Clements, B. W. and A. J. Rogers. 1964. Studies of impounding for the control of salt-marsh mosquitoes in Florida, 1958-1963. Mosq. News 24:265-276.

Gilmore, R. G., D. W. Cooke and C. J. Donohoe. 1982. A comparison of the fish populations and habitat in open and closed salt-marsh impoundments in east-central Florida. Northeast Gulf Sci. 5:25-37.

Harrington, R.W., Jr. and E.S. Harrington. 1961. Food selection among fishes invading a high subtropical salt marsh: from onset of flooding through the progress of a mosquito brood. Ecology 42:646-666.

Harrington, R. W., Jr. and E. S. Harrington. 1982. Effects on fishes and their forage organisms of impounding a Florida salt marsh to prevent breeding by salt marsh mosquitoes. Bull. Mar. Sci. 32:523-531.

Lesser, F. and J.K. Shisler. 1979. Historical development of OMWM in New Jersey: equipment and technique. Proc. Utah Mosq. Abatement Assoc. 25:40-44.

Meredith, W.J., D.E. Saveikis and C.J. Stachecki. 1983. Studies on the environmental effects of "Open Marsh Water Management", a salt-marsh mosquito control technique. Estuaries 6:270.

Meredith, M.J., D.E. Saveikis and C.J. Stachecki. 1985. Guidelines for "Open Marsh Water Management" in Delaware's salt marshes - objectives, system designs, and installation procedures. Wetlands 5: 119-133.

Morris, C.D., R.H. Baker, and W. Opp (eds). 1991. Florida Mosquito Control Handbook. TSR1-22. O'Bryan, P.D., D.B. Carlson and R.G. Gilmore. 1990. Salt marsh mitigation: an example of the process of balancing mosquito control, natural resource and development interests. Fl. Sci. 53:189-203.

Provost, M.W. 1959. Impounding salt marshes for mosquito control...and its effects on bird life. Fl. Naturalist 32 (4), 8 p.

Provost, M.W. 1967. Managing impounded salt marsh for mosquito control and estuarine resource conservation. Marsh & Estuary Management Symposium. p. 163-171.

Ramsey, V. Aquatic Plant Identification Deck. University of Florida, Institute of Food and Agricultural Sciences. 68 pp.

Resh, V.H. and S.S. Balling. 1983. Tidal circulation alteration for salt marsh mosquito control. Environ. Manag. 7:79-84.

Rey, J.R. and T. Kain. 1989. A guide to the salt marsh impoundments of Florida. University of Florida - IFAS, Florida Medical Entomology Laboratory, Vero Beach, FL. 447 pp.

Subcommittee on Managed Marshes. 1996. Information for permit applicants entering the impoundment management plan submittal process. Report to the Fl. Coordinating Council on Mosquito Control. 9 pp.

Subcommittee on Managed Marshes. 1996. Guidelines for salt marsh ditching management plan evaluation. Report to the Fl. Coordinating Council on Mosquito Control. 10 pp.