| "If given an option, not too many people will voluntarily choose to live, work, or play where mosquitoes rule." | |
| Bill Meredith, Delaware Mosquito Control Section |
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As the mosquito-borne West Nile virus spreads across the U.S. , concerns over public health may spur emergency requests to coastal management programs to dredge mosquito ditches, drain wetlands, or spray pesticides on sensitive environmental areas. It can be challenging at best for coastal resource managers to justify environmental concerns when the public’s fears are inflamed.
“Controlling pest species like mosquitoes that can also be disease vectors causing serious public health concerns in our coastal areas is a significant coastal management issue,” says David Carter, environmental program manager for the Delaware Coastal Programs. “Doing it in the least degrading manner to the environment is also a coastal issue and a clear responsibility of all involved.”
As Delaware has learned, proactive collaboration between coastal resource managers and mosquito control program officials can help head off conflicts between agencies, as well as address many environmental concerns, before there is a crisis.
Coastal managers and mosquito control officials “should be working together in any state,” Carter says. “You’ve got to be realistic and balance these things.”
The Right Place
“Location, location, location” appears to have as much meaning for Delaware ’s mosquito control program as it does for siting a successful business. Of the more than 900 mosquito-control programs in the U.S. , Delaware ’s is one of a handful housed within a state fish and wildlife agency.
“We are located as green as we can be located,” says Bill Meredith, program administrator of the Delaware Mosquito Control Section in the Division of Fish and Wildlife. Both Fish and Wildlife and Delaware Coastal Programs are located in the state’s Department of Natural Resources and Environmental Control.
Meredith notes that mosquito control programs in other states are frequently located in agencies where environmental protection is not the primary mission. As a result, these programs are “often at war with people in departments of natural resources,” he says. “Unsightly battles go on in other states and locations.”
Not only does Delaware’s Mosquito Control Section work in the same department with the state’s environmental managers, but Meredith and all the program’s technical staff members are biologists, making them keenly aware of the potential impact on the environment.
Sarah Cooksey, administrator of the Delaware Coastal Program, says, “Because we have a very good relationship with our mosquito control folks, we put a lot of trust with them.”
Sore Spots
The largest sources of problematic coastal mosquitoes in Delaware are salt and brackish marshes along the Delaware River and Bay and around inland bays. Delaware ’s expansive tidal marshes, extensive swampland forests, scattered wet woodlots, and flooded swales can all produce massive swarms of mosquitoes if not controlled.
Given flight ranges of mosquitoes that vary by species from a quarter mile up to 15 to 20 miles, these pests can torment many Delaware residents, visitors, and domestic animals.
“This is the classic conflict of living on the coast,” says Carter. “The coast has bugs.”
“People don’t like to get bit,” adds Meredith. “There is a strong public mandate in Delaware to control mosquitoes because of their adverse impacts to quality of life, public health, and local economies. . . If given an option, not too many people will voluntarily choose to live, work, or play where mosquitoes rule.”
Health Concerns
While mosquitoes have a high nuisance factor and can take a substantial toll on local economies based on tourism, outdoor recreation, or animal husbandry, an important reason to control mosquitoes is the potential impact on public health.
“There’s a whole suite of diseases the public has forgotten about,” Meredith says. “Without continuous and diligent mosquito control efforts, a former era of problematic pestilence would quickly return.”
Up through the early 20 th century, mosquito-borne diseases such as malaria or yellow fever occurred in Delaware and throughout the southeastern states. Meredith says it is thanks to modern mosquito control and medical practices that these diseases are now rare in the U.S.
The primary concern today in Delaware for mosquito-borne disease affecting humans is viral encephalitis, either in the form of eastern equine encephalitis or caused by West Nile virus.
“ West Nile took off so quickly and affected so many people that it served as a reminder to folks that we should always be concerned about these types of outbreaks,” Meredith says.
Since it was first reported in New York in 1999, the virus has made nearly 17,000 Americans ill and killed more than 650. Human, avian, animal, or mosquito West Nile virus infections have been reported in every state except Alaska and Hawaii .
Don’t Be Alarmed
While the public should be aware of West Nile virus and take precautions when outdoors, such as wearing bug spray and long sleeves and pants, Meredith says people should not be overly alarmed.
“The chance that any one person is going to become ill from a single mosquito bite remains quite low,” he says.
Only about one in 150 people infected with the virus will develop severe illness. About 80 percent of people who are infected will not show any symptoms at all.
Early Mistakes
While state and local mosquito control efforts over the past 75 years have helped limit the severity of modern mosquito-borne disease outbreaks in the U.S. , they have sometimes been at the expense of the environment.
In the 1930s, the Civilian Conservation Corps (CCC) dug parallel grid ditches across most of Delaware and other states’ tidal wetlands to control mosquitoes. In Delaware , these ditches were maintained up until the mid 1960s when scientists began to understand that the ditch system unnecessarily drained many wetlands without controlling all mosquito production.
According to Delaware Mosquito Control Section documents published on the Internet, “The long-term negative ramifications of parallel grid ditching on wildlife and salt marsh ecosystems were dramatic.” The drained wetlands lost many large ponds that were valuable nurseries for estuarine fish and invertebrates, and good habitats for waterfowl, wading birds, and shorebirds.
Coastal managers in other states report that public health concerns in the past few years have spurred emergency requests to dredge mosquito ditches that had been mostly abandoned for 20 years. Members of the public, unfamiliar with the value of wetlands, may demand that mosquito control professionals or coastal managers drain or fill wetlands because of concerns about breeding mosquitoes.
“Folks view mosquitoes as coming from the swamp and if you get rid of the swamp, you get rid of mosquitoes,” Meredith explains, “and to some this unwisely and unfortunately becomes an acceptable trade-off.”
Early pesticide use, such as spraying wetlands with fuel oil, arsenic Paris green, or DDT, also had severe environmental impacts.
A New Day
Delaware ’s mosquito control efforts today are implemented with “minimum undesirable environmental impacts,” Meredith says, “and in previously grid-ditched marshes can make environmental improvements, helping to restore valuable surface waters to coastal wetlands.”
The program’s priority is the elimination of mosquito breeding sites. A key technique includes Open Marsh Water Management, used not only to alter mosquito rearing sites and to create habitats for fish that eat mosquito larvae, but also to restore grid-ditched tidal wetlands to a more natural state. The section also manages marsh water levels and tidal exchanges to help lower mosquito production over thousands of acres of Delaware ’s coastal impoundments.
Carter notes that the coastal program provided seven years of funding to the mosquito control program to evaluate and develop Open Marsh Water Management and other marsh restoration techniques.
The Mosquito Control Section has a lead role in the Northern Delaware Wetlands Rehabilitation Program, a collaborative effort by agencies in the Department of Natural Resources and Environmental Control to restore up to 10,000 acres of degraded urban wetlands.
“They are our leading wetlands restoration program,” Carter says.
Other Tools
“Unfortunately,” Meredith says, “in many areas and situations and for many reasons, source reduction methods are not always practicable or permissible to do.” It is then necessary to use insecticides.
While insecticide use can be controversial and things can and sometimes do go wrong in mosquito control, Meredith says there are “science-based dos and don’ts” for mosquito spraying that help ensure environmental compatibility. The section only uses insecticides reviewed and registered by the Environmental Protection Agency (EPA) and carefully applies them using EPA-approved methods.
Meredith says modern mosquitocides are more target-specific and break down within only a few hours to a few days after spraying, helping to avoid or reduce some past problems associated with mosquito control spraying.
When insecticides are needed, the program first uses larvicides to treat immature mosquitoes in their breeding habitats. Meredith says this involves treating smaller areas and is less harmful to the environment.
The program commits to spraying insecticides for adult mosquitoes only as a last resort. “The environment can be protected when adulticiding by choosing the right products, by specific timing of applications within the control season or during the day, and by carefully controlling the spray rate and size of spray droplets, all of which will lessen any unintended impacts,” Meredith says.
He notes that his section is spraying insecticides less than it did a generation ago.
Part of the Plan
Mosquito control is often an issue for protected natural areas, not necessarily to protect their visitors, but to protect the communities that are within flying distance of mosquito breeding areas. This is traditionally an area of conflict between mosquito control officials and resource managers.
In Delaware , the mosquito control section partners with resource managers to treat two federal refuges, as well as a number of state wildlife areas and state parks. The issue of ensuring environmentally sound mosquito control was written into the initial management plan for the Delaware National Estuarine Research Reserve (NERR).
“If they are coming off your land, then you need to do something about it,” notes Carter.
The NERR’s plan addresses insecticides and their use and habitat manipulation for mosquito control.
In addition to proactively addressing mosquito control in the reserve, Carter says he would “welcome the chance to do sound independent research at a NERR site, to help develop some innovative state coastal program policies, and to help guide our mosquito control programs to meet their public pest control responsibilities in our coastal areas in the most environmentally friendly way possible.”
Practically Pest-Free
Many areas in Delaware formerly overrun by mosquitoes are now almost "mosquito-free, or are at least tolerable,” because of the constant behind-the-scenes efforts of mosquito control personnel, Meredith says.
The goal, Carter says, is balancing the impacts on the environment with ensuring people’s quality of life and health, and the economy.
“The big thing is having open dialogue on all these things,” Carter says. “The real concern is that the threat to human life will really spiral out of control and we will lose focus on what we are doing from a policy perspective.”
He adds, “Good science and reasonable policies will help us meet multiple objectives without endangering the public’s health or damaging critical environment.”
For more information on Delaware’s mosquito control efforts, go to www.dnrec.state.de.us/fw/mosquito.htm. You also may contact Bill Meredith at (302) 739-9917, or William.Meredith@state.de.us, or David Carter at (302) 739-9283, or David.Carter@state.de.us. For more information on West Nile virus, point your browser to www.cdc.gov.
