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Biting back: how to craft an integrated mosquito control program.

Winter and early spring are ideal times to evaluate past mosquito control efforts, or to develop or fine-tune a program. Mosquitoes ruin outdoor activities and chase away potential revenue; they also carry life-threatening diseases. For example, West Nile virus has caught the nation's attention since the first human case in North America was reported in 1999. Other mosquito-transmitted diseases include St. Louis encephalitis, Western equine encephalitis, dengue, and canine heartworm.

The good news: It's possible for a public works department to create and implement an effective control strategy. Armed with a basic understanding of habitat and biology--and with help from mosquito control products--you can develop a sound plan.


Step 1: Plan. Begin by devising a plan that considers the extent of your problems and the resources needed to carry out the solution. An integrated plan combines education, monitoring, inspection, mapping of breeding sites, eliminating unnecessary standing water, and treatment. There are many ways to exploit the mosquitoes' own biology and behavior, and to use cost-effective, carefully timed product applications.

Step 2: Organize. Every good program begins with a good organization. People, funding, equipment, and planning are essential. Once the organization and plan have been established, the next step is to monitor populations and identify prime breeding sites. Monitoring larval and adult populations is essential to accurately estimate the need for--and effectiveness of--control measures, and determining where you should concentrate your control efforts. Monitoring methods include:

* Landing counts, which record the number of adults that land on an unprotected arm over a certain period of time

* Light traps that catch adult mosquitoes

* Dip counts, which record the average number of larvae and pupae located on the surface of a body of water.

In Illinois, the Northwest Mosquito Abatement District (NWMAD) focuses most of its effort on annual surveys to locate, map, and inspect areas that foster mosquito production, said NWMAD Director Mike Szyska. "The topography of the district, which covers about 240 square miles of northwest Cook County, is quite diversified," he said.


Mapping and identification of breeding sites is essential. "Our mosquito season is shorter than other areas of the country, but the intensity of mosquito development is significant," said Jim Stark, public affairs coordinator for the Metropolitan Mosquito Control District (MMCD), which provides services to 2.7 million people in the Minneapolis-St. Paul area. This district is one of the largest by land size in the United States, and one of the best funded. "We also have a high density of wetlands in the area, including more than 50,000 identified areas in which mosquitoes develop, ranging from small areas such as freeway ditches to 100-acre swamps," said Stark.

Step 3: Reduce the breeding sites or Iarval habitat. Because water is the critical element in mosquito development, managing standing-water sites is essential. Reducing breeding sites can be as simple as clearing a gutter or removing old tires, or as major as reworking landscaping and ditching in marshlands to improve drainage.



Control programs once relied solely on targeting adult mosquitoes with products called adulticides. The best example of this is fogging, in existence since the 1940s and still a component of control programs. However, in recent years, there have been significant developments in products that reduce reliance on fogging by controlling mosquitoes before they become biting adults.

Biological methods of controlling mosquitoes also have been used with some success. However, there are logistical concerns with their use. The MMCD experimented with use of Gambusia affinis, a fish that feeds on larval mosquitoes. "Gambusia affinis are not a native species in Minnesota, and having to reintroduce them to areas that would completely dry down or freeze during the winter was not practical," said Stark.

While the fish used in Minnesota can be an integrated component, the most commonly used products--larvicides--address the long term. The average female mosquito lays 200 eggs in her lifetime, so it only takes a few females missed by fogging to perpetuate the problem.

Larvicides--which kill mosquitoes before they can develop into biting, breeding adults--comprise the preferred method for preventing future problems and health risks. Stark estimates the MMCD devotes 85% of its resources to larviciding; Szyska estimates 90% of his district's resources are spent on larviciding.

For any larviciding program to be successful, problem breeding sites must be identified and treated. Larvicides such as Altosid, from Schaumburg, Ill.-based Well-mark International, come in several forms to meet specific needs, such as larval habitat, manpower and equipment availabilities, and budget:

* Briquettes and ingots provide consistent, slow-release control to areas where constant maintenance is impractical, such as catch basins, woodland pools, animal drinking troughs, retention basins, and roadside ditches. They may be hand-applied by operators on foot or from moving vehicles (saving time and money), and they come in two residual lengths, offering as much as 150 days of control.

* Liquids come in two concentrations. They are ideal for synchronous broods of mosquitoes that commonly occur in a floodwater habitat, such as tidal marsh and retention overflow. They can also be used to make a sand granule for sites that contain heavy vegetation.

* Pellets offer slow-dissolving, extended control (up to 30 days) for hard-to-treat sites such as marshes, rice fields, mangrove swamps, tire piles, ditches, and other water-holding containers.

* Granules are ideal for large tracts of land, such as pastures and salt marsh. The small particle size ensures even distribution, but granules also lend themselves to treating small pockets of water common around households such as birdbaths and gutters.

The NWMAD employs college students each summer to distribute larvicides in backyard catch basins, sewer grates, floodwater areas, residential areas with standing water, ditches, and culverts. "We use Altosid pellets, ingots, and briquettes because of their residual and long-lasting control, which saves money, labor costs, and continues to provide control even after our summer crews depart to go back to school," said Szyska.


Stark and his MMCD colleagues work closely with the local public works officials to share resources for mapping, cleaning, treating, and working to control the local mosquito population. "Currently MMCD provides all the control, but we hope in the future public works staffs may be able to assist with some treatments," he said. "This may be most important in areas that are difficult to access, or may even be under lock and key. It's all about making the best use of public resources."

District and local public works officials have established a dialogue regarding mosquito control. For example, the district delays larviciding efforts until after the city cleans its catch basins. If the city plans road construction or other activities that would block access to catch basins, the district schedules treatments prior to road closures. "The dialogue is important, because West Nile virus won't go away," said Stark.

--VanGundy is an entomologist with Wellmark International.

For more information, visit the American Mosquito Control Association Web site at

RELATED ARTICLE: A mosquito primer

Adulticides kill adult mosquitoes and can be used in tandem with larvicides. They are necessary when adult mosquitoes migrate into an area, or when an outbreak of disease poses a health threat to a community. Adulticides kill only those mosquitoes in the area at the time of application; repeat applications may be necessary.

Culex mosquitoes, which breed in stagnant water high in organic matter, are the most common source of West Nile virus, encephalitis, and other diseases.

Floodwater mosquitoes lay their eggs on moist soil. The eggs hatch after the soil is flooded but can remain dormant in dry soil for months.

Larvicides kill mosquitoes before they can develop into biting, breeding adults. They usually are target-specific, easy on the environment, effective, efficient, and economical.

Larvae (also known as wrigglers or wigglers) undergo four molts as they develop into pupae. Development may take as little as four days, depending on temperatures and conditions.

Permanent-water mosquitoes lay their eggs on water surfaces in marshes, ponds, catch basins, open containers, and tree holes. The eggs usually hatch in one to three days.

Pupae (or tumblers) rest on the surface of standing water, where they mature into adults unless killed with a larvicide during their larvae stage.
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Title Annotation:Grounds maintenance
Author:VanGundy, Doug
Publication:Public Works
Date:Mar 1, 2006
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